during adolescence,calcium deposited during that period determines the risk of osteoporosis in adulthood.Adverse effects of calcium deficiency have also been observed at adolescence.For instance,it was reportedly associated with bone demineralization in lactating adolescents (Chan et al,1987),and increasing calcium intake reversed the condition.Calcium deficiency apparently increases the risk of bone fracture even among adolescents,as observed among those not meeting 60%of dietary allowance for calcium(Chan et al,1984).It was reported that milk consumption had an impact on bone and body composition in Caucasian pubertal girls(Chan,Hoffman and McMurray,1995).However,the findings of this last study raised controversy(Kerstetter and Insogna 1995;Solomons 1996),with the small sample size recognized as a major weakness.Nevertheless,more significant increases in bone mass and density had been previously observed in a larger study group(Lloyd et al,1993).In Hawaii,Novotny et al(1996) found that a higher consumption of milk during adolescence was among the significant determinants of a higher height of white women compared to Japanese women.Other factors were a higher age at menarche and higher birth weight,but ethnicity was also significant. Does failure to achieve genetically programmed bone mass during teen years leave an irreversible deficit, or is catch-up possible in the 20s?It was believed that peak bone mass was reached by the late teen years (Bonjour et al,1991).However,there is supportive evidence for continuing bone acquisition after the adolescent growth spurt,and calcium intake appears to make a difference,at least in Caucasians(Recker et al,1992).The window for bone building may remain open for a few years after growth in height has stopped(Heany,1998),but there may be wide disparities among populations. Calcium deficiency is associated with high post-menopausal bone loss.Regular consumption of dairy products during adolescence was found to be related to lower levels of post-menopausal bone loss,as shown in a retrospective study of Caucasian American women aged 49-66 years old(Sandler et al,1985). However,many other determinants are at play,and in a cross-sectional study of osteoporotic women in Mexico City,parity was a significant negative factor,while current exercise level and body mass index were positively related to bone mineral mass(Parra-Cabrera et al,1996). While adolescence is a time of high calcium requirements,surveys suggest that adolescent diets are often inadequate in calcium,at least in high income countries such as the USA (Morgan et al,1985). Girls are apparently twice as likely as boys to be deficient,85%vs 43%respectively(Key and Key,1994). Although factors other than diet,in particular exercise,also contribute to calcium status,adequate calcium intake,with supplementation when needed,is recommended in adolescents in the USA.(Key and Key, ibid). However,calcium nutriture in developing countries and in populations other than Caucasians is poorly understood,and it is not known whether osteoporosis may be modulated by calcium intake during childhood and adolescence.This is an area where research is urgently needed.Calcium-deficiency rickets (without vitamin D deficiency)has been reported in children in Africa(Thatcher,Ighogboja and Fischer, 1997)and in Bangladesh(Fischer et al,1999),but the aetiology remains obscure.There are racial differences in the incidence of osteoporosis.While it was considered to be relatively unimportant in developing countries(Scrimgeour 1992),data indicate that it is an increasing problem among women in many Asian countries(Shatrugna 1998),and even in Africa(Aspray et al,1996).There is a pressing need for research on calcium nutriture and osteoporosis in non-Caucasian populations. Evidence from supplementation trials suggests that marginal zinc nutriture may also limit skeletal growth in some infants,children and adolescents(King 1996).In Guatemalan infants,zinc supplementation increased accretion of fat-free mass and enhanced linear growth in those that were stunted at baseline (Rivera et al,1998).Similarly,in a double-blind placebo-controlled study in Viet Nam,growth of stunted children was improved by daily or weekly multi-micronutrient supplements providing zinc,vitamin A, iron and vitamin C (Thu et al,1999).In Japanese boys of short stature with marginal zinc deficiency based on a zinc clearance test,zinc supplements improved the height velocity,but this was not observed in girls(Kaji et al,1998).In Chile also,zinc supplements increased linear growth of stunted pre-adolescent and adolescent males,but not females,in a randomized placebo-controlled trial(Castillo-Duran et al, 1994).Zinc deficiency,with retarded growth among other signs,was first identified among adolescents NUTRITION IN A DOLES C E N C E /21
NUTRITION IN ADOLESCENCE /21 during adolescence, calcium deposited during that period determines the risk of osteoporosis in adulthood. Adverse effects of calcium deficiency have also been observed at adolescence. For instance, it was reportedly associated with bone demineralization in lactating adolescents (Chan et al, 1987), and increasing calcium intake reversed the condition. Calcium deficiency apparently increases the risk of bone fracture even among adolescents, as observed among those not meeting 60% of dietary allowance for calcium (Chan et al, 1984). It was reported that milk consumption had an impact on bone and body composition in Caucasian pubertal girls (Chan, Hoffman and McMurray, 1995). However, the findings of this last study raised controversy (Kerstetter and Insogna 1995; Solomons 1996), with the small sample size recognized as a major weakness. Nevertheless, more significant increases in bone mass and density had been previously observed in a larger study group (Lloyd et al, 1993). In Hawaii, Novotny et al (1996) found that a higher consumption of milk during adolescence was among the significant determinants of a higher height of white women compared to Japanese women. Other factors were a higher age at menarche and higher birth weight, but ethnicity was also significant. Does failure to achieve genetically programmed bone mass during teen years leave an irreversible deficit, or is catch-up possible in the 20s? It was believed that peak bone mass was reached by the late teen years (Bonjour et al, 1991). However, there is supportive evidence for continuing bone acquisition after the adolescent growth spurt, and calcium intake appears to make a difference, at least in Caucasians (Recker et al, 1992). The window for bone building may remain open for a few years after growth in height has stopped (Heany, 1998), but there may be wide disparities among populations. Calcium deficiency is associated with high post-menopausal bone loss. Regular consumption of dairy products during adolescence was found to be related to lower levels of post-menopausal bone loss, as shown in a retrospective study of Caucasian American women aged 49-66 years old (Sandler et al, 1985). However, many other determinants are at play, and in a cross-sectional study of osteoporotic women in Mexico City, parity was a significant negative factor, while current exercise level and body mass index were positively related to bone mineral mass (Parra-Cabrera et al, 1996). While adolescence is a time of high calcium requirements, surveys suggest that adolescent diets are often inadequate in calcium, at least in high income countries such as the USA (Morgan et al, 1985). Girls are apparently twice as likely as boys to be deficient, 85% vs 43% respectively (Key and Key, 1994). Although factors other than diet, in particular exercise, also contribute to calcium status, adequate calcium intake, with supplementation when needed, is recommended in adolescents in the USA. (Key and Key, ibid). However, calcium nutriture in developing countries and in populations other than Caucasians is poorly understood, and it is not known whether osteoporosis may be modulated by calcium intake during childhood and adolescence. This is an area where research is urgently needed. Calcium-deficiency rickets (without vitamin D deficiency) has been reported in children in Africa (Thatcher, Ighogboja and Fischer, 1997) and in Bangladesh (Fischer et al, 1999), but the aetiology remains obscure. There are racial differences in the incidence of osteoporosis. While it was considered to be relatively unimportant in developing countries (Scrimgeour 1992), data indicate that it is an increasing problem among women in many Asian countries (Shatrugna 1998), and even in Africa (Aspray et al, 1996). There is a pressing need for research on calcium nutriture and osteoporosis in non-Caucasian populations. Evidence from supplementation trials suggests that marginal zinc nutriture may also limit skeletal growth in some infants, children and adolescents (King 1996). In Guatemalan infants, zinc supplementation increased accretion of fat-free mass and enhanced linear growth in those that were stunted at baseline (Rivera et al, 1998). Similarly, in a double-blind placebo-controlled study in Viet Nam, growth of stunted children was improved by daily or weekly multi-micronutrient supplements providing zinc, vitamin A, iron and vitamin C (Thu et al, 1999). In Japanese boys of short stature with marginal zinc deficiency based on a zinc clearance test, zinc supplements improved the height velocity, but this was not observed in girls (Kaji et al, 1998). In Chile also, zinc supplements increased linear growth of stunted pre-adolescent and adolescent males, but not females, in a randomized placebo-controlled trial (Castillo-Duran et al, 1994). Zinc deficiency, with retarded growth among other signs, was first identified among adolescents
from middle-eastern areas where the diet included little animal sources of highly bioavailable zinc,and where bread was unleavened,which contributed to a low bioavailability of zinc owing to high phytate content (Sandstead 1991).Zinc-fortified bread was tested on a small scale in a case-control study of Turkey school-age children with low serum zinc levels.Positive results suggesting satisfactory zinc bioavailability were reported(Kilic et al,1998).In adolescent monkeys,moderate zinc deficiency as sole dietary inadequacy was also shown to limit skeletal growth and mineralization(Golub et al,1996). These studies provide further supportive evidence for the involvement of zinc deficiency in stunting, perhaps more so in boys.Zinc may also prevent bone loss,as suggested by observations in older women (Strause et al,1994).Further research should assess the effect of improved zinc intake (or zinc supplementation)during adolescence on the growth spurt,as well as on bone mass and density,in boys and girls.Zinc has other physiological roles,including immunity,and it interacts with several micronutrients,notably with iron(Whittaker 1998),and with vitamin A(Christian and West,1998). In summary,quite a few micronutrients are suspected to be in short supply in adolescence,at least in certain population groups.Remedial and preventive action strategies are discussed in the next chapter. There are many more minerals and vitamins for which deficiencies may occur.However,the purpose is to address those that represent threats to nutritional health at population level based on scientific knowledge to-date,and that are of particular relevance to adolescents'nutrition.Background information on other micronutrients and their deficiencies may be found elsewhere(Latham 1997;WHO 1997b). 3.2.3 Obesity and other nutrition-related chronic diseases At the present time,cardiovascular disease and cancer are responsible for half as many deaths in the developing as in the developed world.However,this is changing as obesity and associated chronic diseases (cardiovascular disease and diabetes in particular)are increasing at a rapid rate in many developing countries,to the extent that diet-related chronic diseases are considered a new challenge in the Millennium (James 1998).Obesity has become a global pandemic and should be regarded as today's principal neglected public health problem(WHO 1998a). 3.2.3.1 Obesity Obesity is increasing in most high-income countries,in developing countries undergoing nutrition transition,and even in poor countries with current food insecurity and undernutrition problems.In Ghanian adults,for instance,underweight(BMI<18.4)is only slightly more prevalent than overweight (BMI>25)(International Obesity Task Force(IOTF)11 The body of data on prevalence of obesity and secular trends in adults is growing and there is now a coherent system available for use at the international level to classify adult overweight and obesity based on BMI(WHO 1998a).However,such data are lacking for children and adolescents,owing in part to lack of agreement and consistency in classification of obesity (see Section 4.3.1).A roughly twofold increase in the frequency of overweight or obesity was nonetheless reported over a twenty-year period in American and Japanese schoolchild groups(WHO 1998a). In Europe,the prevalence of adult obesity has reportedly increased by about 10%-40%in the last 10 years,and the most dramatic increase(50%since 1980)has been observed in the UK'.However,there is no specific data on adolescents.In a study on cardiovascular risk factors in Italian adolescents attending junior high schools(Rabbia et al,1994),the prevalence of obesity,based on BMI reference data from the UK,was 24%in boys and 19%in girls,and 39%of the remaining boys and 38%of the remaining girls were in the overweight range.Interestingly,the prevalence was significantly higher in boys than in girls, which is at variance with most studies. Donald B.Brown Research Chair on Obesity,www.obesity.chair.ulaval.ca/IOTEhtm(14/05/99) 22
22/ 11 Donald B. Brown Research Chair on Obesity, www.obesity.chair.ulaval.ca/IOTF.htm (14/05/99) from middle-eastern areas where the diet included little animal sources of highly bioavailable zinc, and where bread was unleavened, which contributed to a low bioavailability of zinc owing to high phytate content (Sandstead 1991). Zinc-fortified bread was tested on a small scale in a case-control study of Turkey school-age children with low serum zinc levels. Positive results suggesting satisfactory zinc bioavailability were reported (Kilic et al, 1998). In adolescent monkeys, moderate zinc deficiency as sole dietary inadequacy was also shown to limit skeletal growth and mineralization (Golub et al, 1996). These studies provide further supportive evidence for the involvement of zinc deficiency in stunting, perhaps more so in boys. Zinc may also prevent bone loss, as suggested by observations in older women (Strause et al, 1994). Further research should assess the effect of improved zinc intake (or zinc supplementation) during adolescence on the growth spurt, as well as on bone mass and density, in boys and girls. Zinc has other physiological roles, including immunity, and it interacts with several micronutrients, notably with iron (Whittaker 1998), and with vitamin A (Christian and West, 1998). In summary, quite a few micronutrients are suspected to be in short supply in adolescence, at least in certain population groups. Remedial and preventive action strategies are discussed in the next chapter. There are many more minerals and vitamins for which deficiencies may occur. However, the purpose is to address those that represent threats to nutritional health at population level based on scientific knowledge to-date, and that are of particular relevance to adolescents’ nutrition. Background information on other micronutrients and their deficiencies may be found elsewhere (Latham 1997; WHO 1997b). 3.2.3 Obesity and other nutrition-related chronic diseases At the present time, cardiovascular disease and cancer are responsible for half as many deaths in the developing as in the developed world. However, this is changing as obesity and associated chronic diseases (cardiovascular disease and diabetes in particular) are increasing at a rapid rate in many developing countries, to the extent that diet-related chronic diseases are considered a new challenge in the Millennium (James 1998). Obesity has become a global pandemic and should be regarded as today’s principal neglected public health problem (WHO 1998a). 3.2.3.1 Obesity Obesity is increasing in most high-income countries, in developing countries undergoing nutrition transition, and even in poor countries with current food insecurity and undernutrition problems. In Ghanian adults, for instance, underweight (BMI <18.4) is only slightly more prevalent than overweight (BMI>25) (International Obesity Task Force (IOTF)11 . The body of data on prevalence of obesity and secular trends in adults is growing and there is now a coherent system available for use at the international level to classify adult overweight and obesity based on BMI (WHO 1998a). However, such data are lacking for children and adolescents, owing in part to lack of agreement and consistency in classification of obesity (see Section 4.3.1). A roughly twofold increase in the frequency of overweight or obesity was nonetheless reported over a twenty-year period in American and Japanese schoolchild groups (WHO 1998a). In Europe, the prevalence of adult obesity has reportedly increased by about 10%-40% in the last 10 years, and the most dramatic increase (50% since 1980) has been observed in the UK1 . However, there is no specific data on adolescents. In a study on cardiovascular risk factors in Italian adolescents attending junior high schools (Rabbia et al, 1994), the prevalence of obesity, based on BMI reference data from the UK, was 24% in boys and 19% in girls, and 39% of the remaining boys and 38% of the remaining girls were in the overweight range. Interestingly, the prevalence was significantly higher in boys than in girls, which is at variance with most studies
In the United States,the Third National Health and Nutrition Examination Survey(NHANES III,1988- 94)revealed that the prevalence of overweight has continued to increase (Update 1997).Roughly one third of adults were overweight(based on 85th percentile of NHANES II BMI for age,1976-80)and 12% of adolescents(based on 95th percentile of BMI for age),which represents a twofold increase.In the Minnesota Adolescent Health Survey (Neumark-Sztainer et al,1998),there was a strong inverse relationship between socioeconomic status and weight status in girls,but not in boys. The situation in developing countries varies widely according to urbanization and income,but obesity is not merely a problem of high-income groups.In Cali,for instance,median BMI and skinfold values are higher than the American reference population for all levels of income,but it is significantly higher in the middle-income group(Pradilla,personal communication).In countries undergoing rapid economic growth,in China for example(Popkin et al,1993),a nutrition transition is observed,with a progressive change of patterns of nutrition-related disease.In such contexts,undernutrition and overnutrition commonly co-exist.As problems of food scarcity are solved and incomes rise,there is a rapid change in the structure of diets and the level of physical activity.In China,it was found that overweight was emerging as a problem associated with young age,high income and urban adolescence (Wang,Popkin and Zhai,1998),although the prevalence of 4%(85th percentile of reference BMI, NHANES II)was still quite low compared with developed countries.It can in part be ascribed to changing eating patterns and in this study,27%of the some 4000 adolescents studied derived more than 30%of their energy from dietary fat and 16%had more than 10%of their food energy provided by saturated fat.It was also observed that urban girls from a lower socioeconomic status were more at increased risk of overweight than those of a higher income level.This higher rate of obesity in poorer groups is also typical in developed countries.Among Amerindians,for instance(First Nations of North America), obesity has become a serious epidemic,much like diabetes,which is associated with it(Gohdes 1995; Delisle and Favron,1994;Delisle,Rivard and Ekoe,1995). In the Middle East,there have been several reports of increasing obesity among adolescents and adults Based on a BMI cut-off of 25 for overweight or obesity,16%of boys and 17%of girls in secondary schools in Bahrain were positive(Abdulrahman 1993).While obesity increased with age in girls,it declined in boys.A family history of obesity was a significant factor associated with obesity in both boys and girls.An interesting observation is that boys who ate alone were three times more likely to become obese than those who ate with family members.In United Arab Emirates(Amine and Samy,1996),a 11%rate of overweight (110-120%reference weight for height)and 31%of obesity (120%of reference weight) were reported among female university students.The prevalence of obesity increased with age and was associated with obesity in childhood or in parent(s),as well as with between-meal food intake,particularly fast food,with limited physical activity and with long afternoon napping.In Kuwaiti college girls,Al-Isa (1998)reported that 27%were overweight(BMI>25)and 7%were obese(BMI>30).Obesity among parents and dieting were among the independent and significant factors. Obesity and chronic malnutrition reflected in stunting often co-exist.They may even be interrelated, with more obesity among stunted people,which would tend to support Barker's hypothesis of increased chronic disease risk among people having been exposed to malnutrition in early life(Barker 1996;Leon et al,1996).In poor areas of urban Brazil,for instance,it was found that obesity associated with stunting was more common than obesity without stunting,both in younger children and adolescents(Sawaya et al,1995).A high risk of obesity among stunted children has also been described in other developing countries undergoing nutrition transition(Popkin et al,1996).In such circumstances,however,a higher relative weight because of stunting may not reflect excessive adiposity (WHO 1998a),and cautious interpretation is needed.Adolescents who were growth-retarded at birth also tend to put on more weight during the growth spurt of adolescence(Leger and Czernichow,1999).Another aspect that may further complicate the interpretation of adolescent anthropometry is that early maturing subjects are in general more obese in their twenties than slowly maturing adolescents,according to the Amsterdam health and growth study(Post and Kemper 1993;van Lenthe et al,1996).It is suggested that early maturation which responds to genetic and environmental factors,including high level of nutrition,may be a risk indicator for the development of obesity. NUTRI TION IN A DOLE S C E N C E /23
NUTRITION IN ADOLESCENCE /23 In the United States, the Third National Health and Nutrition Examination Survey (NHANES III, 1988- 94) revealed that the prevalence of overweight has continued to increase (Update 1997). Roughly one third of adults were overweight (based on 85th percentile of NHANES II BMI for age, 1976-80) and 12% of adolescents (based on 95th percentile of BMI for age), which represents a twofold increase. In the Minnesota Adolescent Health Survey (Neumark-Sztainer et al, 1998), there was a strong inverse relationship between socioeconomic status and weight status in girls, but not in boys. The situation in developing countries varies widely according to urbanization and income, but obesity is not merely a problem of high-income groups. In Cali, for instance, median BMI and skinfold values are higher than the American reference population for all levels of income, but it is significantly higher in the middle-income group (Pradilla, personal communication). In countries undergoing rapid economic growth, in China for example (Popkin et al, 1993), a nutrition transition is observed, with a progressive change of patterns of nutrition-related disease. In such contexts, undernutrition and overnutrition commonly co-exist. As problems of food scarcity are solved and incomes rise, there is a rapid change in the structure of diets and the level of physical activity. In China, it was found that overweight was emerging as a problem associated with young age, high income and urban adolescence (Wang, Popkin and Zhai, 1998), although the prevalence of 4% (85th percentile of reference BMI, NHANES II) was still quite low compared with developed countries. It can in part be ascribed to changing eating patterns and in this study, 27% of the some 4000 adolescents studied derived more than 30% of their energy from dietary fat and 16% had more than 10% of their food energy provided by saturated fat. It was also observed that urban girls from a lower socioeconomic status were more at increased risk of overweight than those of a higher income level. This higher rate of obesity in poorer groups is also typical in developed countries. Among Amerindians, for instance (First Nations of North America), obesity has become a serious epidemic, much like diabetes, which is associated with it (Gohdes 1995; Delisle and Favron, 1994; Delisle, Rivard and Ékoé, 1995). In the Middle East, there have been several reports of increasing obesity among adolescents and adults. Based on a BMI cut-off of 25 for overweight or obesity, 16% of boys and 17% of girls in secondary schools in Bahrain were positive (Abdulrahman 1993). While obesity increased with age in girls, it declined in boys. A family history of obesity was a significant factor associated with obesity in both boys and girls. An interesting observation is that boys who ate alone were three times more likely to become obese than those who ate with family members. In United Arab Emirates (Amine and Samy, 1996), a 11% rate of overweight (110-120% reference weight for height) and 31% of obesity (120% of reference weight) were reported among female university students. The prevalence of obesity increased with age and was associated with obesity in childhood or in parent(s), as well as with between-meal food intake, particularly fast food, with limited physical activity and with long afternoon napping. In Kuwaiti college girls, Al-Isa (1998) reported that 27% were overweight (BMI>25) and 7% were obese (BMI>30). Obesity among parents and dieting were among the independent and significant factors. Obesity and chronic malnutrition reflected in stunting often co-exist. They may even be interrelated, with more obesity among stunted people, which would tend to support Barker’s hypothesis of increased chronic disease risk among people having been exposed to malnutrition in early life (Barker 1996; Leon et al, 1996). In poor areas of urban Brazil, for instance, it was found that obesity associated with stunting was more common than obesity without stunting, both in younger children and adolescents (Sawaya et al, 1995). A high risk of obesity among stunted children has also been described in other developing countries undergoing nutrition transition (Popkin et al, 1996). In such circumstances, however, a higher relative weight because of stunting may not reflect excessive adiposity (WHO 1998a), and cautious interpretation is needed. Adolescents who were growth-retarded at birth also tend to put on more weight during the growth spurt of adolescence (Léger and Czernichow, 1999). Another aspect that may further complicate the interpretation of adolescent anthropometry is that early maturing subjects are in general more obese in their twenties than slowly maturing adolescents, according to the Amsterdam health and growth study (Post and Kemper 1993; van Lenthe et al, 1996). It is suggested that early maturation which responds to genetic and environmental factors, including high level of nutrition, may be a risk indicator for the development of obesity
The health consequences of overweight and obesity in adolescence have been thoroughly reviewed (WHO 1998a).Obesity-related symptoms in children and adolescents include psychosocial problems,increased cardiovascular risk factors,abnormal glucose metabolism,hepatic gastrointestinal disturbances,sleep apnoea (in children)and orthopedic complications.Obesity in adolescence may have serious health and psychosocial consequences.For some,the greatest hazards of adolescent obesity are the social and psychological difficulties that also may persist into the adult years (Lifshitz,Tarim and Smith,1993), although for others,obesity in adolescence may have limited emotional implications(Elster and Kuznets, 1995).Adolescents are sensitive about body image and obese teenagers are especially vulnerable to social discrimination.Poor self-esteem and body image are consistently associated with obesity in adolescents, but not in younger children(French,Story and Perry,1995).In women,obesity at adolescence may even affect future socioeconomic and marital status,according to a longitudinal study in the USA(Gortmaker etal,1993) The major long-term health problems associated with adolescent obesity are its persistence in adult life and its association with cardiovascular disease risk in later life.Obesity that persisted through age 12 raised the odds of adult obesity to 4 to I in the UK(Stark et al,1981).Based on the Harvard Growth Study,males who were overweight at age 13-18 were found to be at increased risk of mortality five to six decades later,compared to subjects who were lean during adolescence(Must et al,1992).In general, longitudinal studies suggest that obesity tracks into adulthood particularly if it is present in adolescence (Serdula et al,1993).While a genetic component in the aetiology is acknowledged,environmental factors play a central role.High-fat diets and sedentary lifestyles are considered major causes(WHO 1998a). For instance,in a study among adolescent Cree Indians in Canada,it was found that the rate of obesity was high,and that it was associated,among other factors,with the amount of time spent viewing TV (Bernard et al,1995),an observation that had previously been made in quite a few studies on childhood obesity.Foetal malnutrition as an additional risk factor has been discussed above. It is estimated that half of cardiovascular disease mortality is nutrition-related,as well as 33%to 50%of type-2 diabetes cases(WHO 1990).In a 14-year longitudinal study of over 6000 obese subjects in Germany,it was found that in all age groups,there was an increased mortality risk with obesity,and the risk increased with the level of obesity as assessed on the basis of BMI(Bender et al,1999).The obesity- related increased risk was higher in younger age groups,and declined with age.The highest mortality was observed in the group aged 18-29 years at baseline.In a long-term follow-up study of adolescents (Must et al,1992),it was found that adolescent boys with a BMI above the 75th centile were at increased risk of death from all causes,from cardiovascular disease,and even from colorectal cancer,and both overweight boys and girls were at increased morbidity risk. 3.2.3.2 Cardiovascular disease risks Atherosclerosis and blood lipids Obesity is defined as excess adiposity,and high BMI is merely an indicator.It is established that beyond the amount of body fat,its distribution affects metabolic disease risk.Even before adulthood, anthropometric measures of adiposity were found to be related to lipid and insulin concentrations,in a cross-sectional study of Bogalusa children and adolescents(Freedman et al,1995;1999).A central or abdominal distribution of body fat was related to adverse concentrations of triacylglycerides,LDL-and HDL-cholesterol,and insulin.This was observed,whether fat distribution was assessed by measuring waist circumference alone,after adjusting waist circumference for weight and height,or with the waist- hip ratio.Waist circumference showed the most consistent association with risk factors,which clarifies previously conflicting results on fat distribution and biological risk markers.Thus measuring waist circumference of adolescents,in addition to BMI,could help identify those who likely have adverse lipid and insulin concentrations,and who should be targeted for weight reduction and risk-factor surveillance Freedman et al (ibid.)provide 50th and 90th percentile values for white and for black girls and boys,from age 5 to 17(See Table in Appendix II).However,anthropometric indices of fat distribution may vary across population groups of adolescents as they do in adults(Karter et al,1996)and therefore,additional studies in adolescents are required.Waist-hip ratios are also difficult to standardize in children because of changes in body habitus with normal development(Gidding et al,1996)
24/ The health consequences of overweight and obesity in adolescence have been thoroughly reviewed (WHO 1998a). Obesity-related symptoms in children and adolescents include psychosocial problems, increased cardiovascular risk factors, abnormal glucose metabolism, hepatic gastrointestinal disturbances, sleep apnoea (in children) and orthopedic complications. Obesity in adolescence may have serious health and psychosocial consequences. For some, the greatest hazards of adolescent obesity are the social and psychological difficulties that also may persist into the adult years (Lifshitz, Tarim and Smith, 1993), although for others, obesity in adolescence may have limited emotional implications (Elster and Kuznets, 1995). Adolescents are sensitive about body image and obese teenagers are especially vulnerable to social discrimination. Poor self-esteem and body image are consistently associated with obesity in adolescents, but not in younger children (French, Story and Perry, 1995). In women, obesity at adolescence may even affect future socioeconomic and marital status, according to a longitudinal study in the USA (Gortmaker et al, 1993). The major long-term health problems associated with adolescent obesity are its persistence in adult life and its association with cardiovascular disease risk in later life. Obesity that persisted through age 12 raised the odds of adult obesity to 4 to 1 in the UK (Stark et al, 1981). Based on the Harvard Growth Study, males who were overweight at age 13-18 were found to be at increased risk of mortality five to six decades later, compared to subjects who were lean during adolescence (Must et al, 1992). In general, longitudinal studies suggest that obesity tracks into adulthood particularly if it is present in adolescence (Serdula et al, 1993). While a genetic component in the aetiology is acknowledged, environmental factors play a central role. High-fat diets and sedentary lifestyles are considered major causes (WHO 1998a). For instance, in a study among adolescent Cree Indians in Canada, it was found that the rate of obesity was high, and that it was associated, among other factors, with the amount of time spent viewing TV (Bernard et al, 1995), an observation that had previously been made in quite a few studies on childhood obesity. Foetal malnutrition as an additional risk factor has been discussed above. It is estimated that half of cardiovascular disease mortality is nutrition-related, as well as 33% to 50% of type-2 diabetes cases (WHO 1990). In a 14-year longitudinal study of over 6000 obese subjects in Germany, it was found that in all age groups, there was an increased mortality risk with obesity, and the risk increased with the level of obesity as assessed on the basis of BMI (Bender et al, 1999). The obesityrelated increased risk was higher in younger age groups, and declined with age. The highest mortality was observed in the group aged 18-29 years at baseline. In a long-term follow-up study of adolescents (Must et al, 1992), it was found that adolescent boys with a BMI above the 75th centile were at increased risk of death from all causes, from cardiovascular disease, and even from colorectal cancer, and both overweight boys and girls were at increased morbidity risk. 3.2.3.2 Cardiovascular disease risks • Atherosclerosis and blood lipids Obesity is defined as excess adiposity, and high BMI is merely an indicator. It is established that beyond the amount of body fat, its distribution affects metabolic disease risk. Even before adulthood, anthropometric measures of adiposity were found to be related to lipid and insulin concentrations, in a cross-sectional study of Bogalusa children and adolescents (Freedman et al, 1995; 1999). A central or abdominal distribution of body fat was related to adverse concentrations of triacylglycerides, LDL- and HDL-cholesterol, and insulin. This was observed, whether fat distribution was assessed by measuring waist circumference alone, after adjusting waist circumference for weight and height, or with the waisthip ratio. Waist circumference showed the most consistent association with risk factors, which clarifies previously conflicting results on fat distribution and biological risk markers. Thus measuring waist circumference of adolescents, in addition to BMI, could help identify those who likely have adverse lipid and insulin concentrations, and who should be targeted for weight reduction and risk-factor surveillance. Freedman et al (ibid.) provide 50th and 90th percentile values for white and for black girls and boys, from age 5 to 17 (See Table in Appendix II). However, anthropometric indices of fat distribution may vary across population groups of adolescents as they do in adults (Karter et al, 1996) and therefore, additional studies in adolescents are required. Waist-hip ratios are also difficult to standardize in children because of changes in body habitus with normal development (Gidding et al, 1996)
Atherosclerosis can be recognized at postmortem,and it correlates with antemortem levels of lipids even in adolescents(Newman,Wattigney and Berenson,1991).Fibrous plaques are often already evident in adolescence(McGill et al,1997).In male adolescents for the Netherlands(but not in females),Lund et al(1992)found that dietary fatty acid profiles were significantly correlated with several parameters of plasma lipid status,notably with the ratio of total cholesterol:HDL cholesterol,which is a risk factor for coronary heart disease.In a study on over 500 Egyptian adolescent girls attending a middle-class school in an urban area(Hakim et al,1997),one third had high blood cholesterol (total>200 mg/dl).It was also found that nearly two thirds were overweight,based on BMI>25.BMI and upper body fat pattern (subscapular/triceps skinfold)explained 25%of cholesterol variance.Tracking from childhood through adulthood of cardiovascular risk factors,which tend to cluster together,has been recognised(Freedman et al,1985;Bao et al,1994).Since atherosclerosis(and risk factors such as hyperlipidemia)begins in childhood and progresses into adulthood,as shown in many studies including Bogalusa and Muscatine (Lauer and Clarke,1990),it is important to identify children and adolescents at higher risk based on obesity,upper-body adiposity,a family history and,when possible,current lipid abnormalities. According to NHANES III(Hickman et al,1998)as in previous surveys in the USA,it was found that mean total cholesterol was higher in female than male adolescents,and that the highest levels were found in 9 to 11-year olds.There was a declining trend,as in adults,from previous studies among all 12 to 17 year-old adolescent race/sex groups(Mexican-Americans,non-hispanic whites),except in black females,who had the highest total serum cholesterol levels,and who experienced the smallest decrease over time.This may be related to the higher observed rate of obesity among black adolescents,compared with Mexican-Americans and whites.The declining trend in serum cholesterol accompanies a decreasing level of total and saturated fat intake as of total calories,and declining cholesterol intake,although intake levels are still too high.Overweight is also highly prevalent,and adolescents show a low level of physical activity.However,total serum cholesterol does not distinguish between "bad"and "good" cholesterol,which fluctuates during puberty.For instance,the decline of total cholesterol at puberty in males reflects the decrease of HDL-cholesterol. ·Hypertension High blood pressure in childhood and adolescence may be associated with impaired foetal growth evidenced by low birth weight,and this was also observed in Africa(Pharaoh et al,1998;Woelk et al, 1998).For instance,in the retrospective study in Harare schoolchildren(Woelk et al,ibid.),a slight but significant inverse association between systolic blood pressure and birth weight was observed,even after controlling for present body weight.Similar findings were reported in Jamaican schoolchildren(Forrester et al,1996).In a 15-year cohort study of very-low-birth-weight infants in England,control matched for age,sex and school(Pharaoh et al,1998),systolic blood pressure was significantly higher in cases than controls,and the difference was further increased after adjusting for anthropometric measurements. The difference from controls was 4-5 mm Hg,which is not unimportant.However,some of the variation could be attributed to socioeconomic differences,beyond foetal development,and according to the authors,it is plausible that adverse social and economic influences initiate their cardiovascular effects during intrauterine life,and are compounded during childhood,adolescence and adulthood.This is in agreement with the social patterning theory(Kuh et al,1997)referred to in Chapter 2.The association between blood pressure and birth weight is reportedly less consistent in adolescents than in children or adults(Barker 1994).Other nutrition-related chronic diseases such as CVD,NIDDM and certain types of cancer may only appear in adult life,but are associated with dietary and lifestyle risk factors at adolescence,many of which are in association with obesity. 3.2.3.3 Nutrition,gout and gallstones Overweight and obese adults are at increased risk for mortality and morbidity associated with many acute and chronic conditions,including gallbladder disease and gout. Obesity,a high purine diet,and regular alcohol consumption are well-known risk factors for gout (Emmerson 1996).Evidence suggests that a sedentary lifestyle,and a diet rich in animal fat,in refined sugars,and poor in vegetable fats and fibre are also significant risk factors for gallstone formation NUTRI TION IN A DOLE S C E N C E /25
NUTRITION IN ADOLESCENCE /25 Atherosclerosis can be recognized at postmortem, and it correlates with antemortem levels of lipids even in adolescents (Newman, Wattigney and Berenson, 1991). Fibrous plaques are often already evident in adolescence (McGill et al, 1997). In male adolescents for the Netherlands (but not in females), Lund et al (1992) found that dietary fatty acid profiles were significantly correlated with several parameters of plasma lipid status, notably with the ratio of total cholesterol:HDL cholesterol, which is a risk factor for coronary heart disease. In a study on over 500 Egyptian adolescent girls attending a middle-class school in an urban area (Hakim et al, 1997), one third had high blood cholesterol (total>200 mg/dl). It was also found that nearly two thirds were overweight, based on BMI>25. BMI and upper body fat pattern (subscapular/triceps skinfold) explained 25% of cholesterol variance. Tracking from childhood through adulthood of cardiovascular risk factors, which tend to cluster together, has been recognised (Freedman et al, 1985; Bao et al, 1994). Since atherosclerosis (and risk factors such as hyperlipidemia) begins in childhood and progresses into adulthood, as shown in many studies including Bogalusa and Muscatine (Lauer and Clarke, 1990), it is important to identify children and adolescents at higher risk based on obesity, upper-body adiposity, a family history and, when possible, current lipid abnormalities. According to NHANES III (Hickman et al, 1998) as in previous surveys in the USA, it was found that mean total cholesterol was higher in female than male adolescents, and that the highest levels were found in 9 to 11-year olds. There was a declining trend, as in adults, from previous studies among all 12 to 17 year-old adolescent race/sex groups (Mexican-Americans, non-hispanic whites), except in black females, who had the highest total serum cholesterol levels, and who experienced the smallest decrease over time. This may be related to the higher observed rate of obesity among black adolescents, compared with Mexican-Americans and whites. The declining trend in serum cholesterol accompanies a decreasing level of total and saturated fat intake as % of total calories, and declining cholesterol intake, although intake levels are still too high. Overweight is also highly prevalent, and adolescents show a low level of physical activity. However, total serum cholesterol does not distinguish between “bad” and “good” cholesterol, which fluctuates during puberty. For instance, the decline of total cholesterol at puberty in males reflects the decrease of HDL-cholesterol. • Hypertension High blood pressure in childhood and adolescence may be associated with impaired foetal growth evidenced by low birth weight, and this was also observed in Africa (Pharaoh et al, 1998; Woelk et al, 1998). For instance, in the retrospective study in Harare schoolchildren (Woelk et al, ibid.), a slight but significant inverse association between systolic blood pressure and birth weight was observed, even after controlling for present body weight. Similar findings were reported in Jamaican schoolchildren (Forrester et al, 1996). In a 15-year cohort study of very-low-birth-weight infants in England, control matched for age, sex and school (Pharaoh et al, 1998), systolic blood pressure was significantly higher in cases than controls, and the difference was further increased after adjusting for anthropometric measurements. The difference from controls was 4-5 mm Hg, which is not unimportant. However, some of the variation could be attributed to socioeconomic differences, beyond foetal development, and according to the authors, it is plausible that adverse social and economic influences initiate their cardiovascular effects during intrauterine life, and are compounded during childhood, adolescence and adulthood. This is in agreement with the social patterning theory (Kuh et al, 1997)referred to in Chapter 2. The association between blood pressure and birth weight is reportedly less consistent in adolescents than in children or adults (Barker 1994). Other nutrition-related chronic diseases such as CVD, NIDDM and certain types of cancer may only appear in adult life, but are associated with dietary and lifestyle risk factors at adolescence, many of which are in association with obesity. 3.2.3.3 Nutrition, gout and gallstones Overweight and obese adults are at increased risk for mortality and morbidity associated with many acute and chronic conditions, including gallbladder disease and gout. Obesity, a high purine diet, and regular alcohol consumption are well-known risk factors for gout (Emmerson 1996). Evidence suggests that a sedentary lifestyle, and a diet rich in animal fat, in refined sugars, and poor in vegetable fats and fibre are also significant risk factors for gallstone formation