3.2.1.2 Malnutrition delays physical growth and maturation There are wide variations among populations in median age at menarche,which ranges from 12.5 years in high income countries,to 15 and above in poorer countries(Becker 1993).Several factors are likely involved in this variance,and nutritional status is considered to be a major one(Bongaarts and Cohen, 1998).Evidence is of four types.First,a relationship between nutritional intakes and the timing of puberty onset has been observed in many populations,with better nourished girls reaching menarche earlier than undernourished girls.Secondly,anthropometric indices of growth and the timing of puberty onset are correlated in humans and many other species alike.Third,a gradual reduction in age of menarche has been observed with progressive improvements in socioeconomic conditions and nutrition over the last 200 years in western societies.And conversely,studies across populations show a negative correlation between SES and the age of menarche.However,poor health status and psychological stress are correlates of poor nutrition that may also delay the onset of menarche in lower SES groups.It is suggested that the mechanism by which undernutrition delays or suppresses activity of the reproductive axis in adolescents or adult women,is through decreased available energy,rather than body composition changes(Cameron 1996),as suggested by rapid reversal of exercise-induced reproductive dysfunction by increasing food intake,without long-term negative effect on reproductive capacity. Among girls,the "growth spurt"normally takes place between 12 and 18 months before the onset of menarche,which occurs between the ages of 10 and 14.Then growth in stature continues for up to 7 years.Growth of pelvic bones continues for another 2-3 years after height growth has stopped(Moerman 1982).Maximum bone mass is not achieved before 25 years(National Academy of Sciences 1997). In undernourished populations,growth rate during adolescence is slower(Eveleth and Tanner,1990). Using maximum growth spurt or menarche as an indicator,maturation may be delayed in malnourished girls by an average of two years (Dreizen,Spirakis and Stone,1967).Growth is delayed,when it is not depressed.There are differences according to socioeconomic level,and there may also be ethnic differences that are not fully accounted for by environmental conditions.For instance,in Guatemala,median age at menarche is significantly higher in Indian adolescents living in rural areas than in non-Indians;lowest age is among the urban,non-Indian Guatemalans.Age at menarche is also inversely associated with weight, arm circumference,height,and BMI(Delgado and Hurtado,1990).In Nigeria,it was found that schoolgirls from the upper socioeconomic class reached menarche 11 months earlier than the lower socioeconomic counterparts (Abioye-Kuteyi et al,1997).In India,it was observed that peak weight and height velocities were delayed by 18 months for children who were stunted at 10 years of age(Kanade 1994).Spontaneous or intervention-related catch-up growth during adolescence is discussed in Chapter 2. 3.2.1.3 Stunting and delayed maturation compound risk of adolescent pregnancy Short stature is oftentimes associated with small pelvises in women,and this is an important risk factor for obstructed labour.The risk rises sharply when the stature is below 1.45 m,which is the case of 16- 18%of women in Asia,11-15%of women in Latin America and 3%in Africa(ACC/SCN 1992a). So maternal stunting is a factor of increased obstetric risk,and it can be attributed to chronic malnutrition, at least in part.In addition,delayed growth and maturation in girls as a result of malnutrition further increases the risks associated with adolescent pregnancy,as biological age lags behind chronological age (see under Section 3.3). 3.2.1.4 Malnutrition reduces work capacity Adolescents'contribution to agricultural and domestic chores is critical in many populations and it is suspected that undernutrition(and stunting)might limit work capacity and endurance of both boys and girls.The relationship between nutritional status and productivity is complex,as discussed by Kennedy and Garcia(1994),and there have been very few specific studies on adolescents.What is nonetheless suggested by available data from various studies and countries is that BMI,fat free mass and height are associated with increased time devoted to work and with work capacity.Early malnutrition 6
16/ 3.2.1.2 Malnutrition delays physical growth and maturation There are wide variations among populations in median age at menarche, which ranges from 12.5 years in high income countries, to 15 and above in poorer countries (Becker 1993). Several factors are likely involved in this variance, and nutritional status is considered to be a major one (Bongaarts and Cohen, 1998). Evidence is of four types. First, a relationship between nutritional intakes and the timing of puberty onset has been observed in many populations, with better nourished girls reaching menarche earlier than undernourished girls. Secondly, anthropometric indices of growth and the timing of puberty onset are correlated in humans and many other species alike. Third, a gradual reduction in age of menarche has been observed with progressive improvements in socioeconomic conditions and nutrition over the last 200 years in western societies. And conversely, studies across populations show a negative correlation between SES and the age of menarche. However, poor health status and psychological stress are correlates of poor nutrition that may also delay the onset of menarche in lower SES groups. It is suggested that the mechanism by which undernutrition delays or suppresses activity of the reproductive axis in adolescents or adult women, is through decreased available energy, rather than body composition changes (Cameron 1996), as suggested by rapid reversal of exercise-induced reproductive dysfunction by increasing food intake, without long-term negative effect on reproductive capacity. Among girls, the “growth spurt” normally takes place between 12 and 18 months before the onset of menarche, which occurs between the ages of 10 and 14. Then growth in stature continues for up to 7 years. Growth of pelvic bones continues for another 2-3 years after height growth has stopped (Moerman 1982). Maximum bone mass is not achieved before 25 years (National Academy of Sciences 1997). In undernourished populations, growth rate during adolescence is slower (Eveleth and Tanner, 1990). Using maximum growth spurt or menarche as an indicator, maturation may be delayed in malnourished girls by an average of two years (Dreizen, Spirakis and Stone, 1967). Growth is delayed, when it is not depressed. There are differences according to socioeconomic level, and there may also be ethnic differences that are not fully accounted for by environmental conditions. For instance, in Guatemala, median age at menarche is significantly higher in Indian adolescents living in rural areas than in non-Indians; lowest age is among the urban, non-Indian Guatemalans. Age at menarche is also inversely associated with weight, arm circumference, height, and BMI (Delgado and Hurtado, 1990). In Nigeria, it was found that schoolgirls from the upper socioeconomic class reached menarche 11 months earlier than the lower socioeconomic counterparts (Abioye-Kuteyi et al, 1997). In India, it was observed that peak weight and height velocities were delayed by 18 months for children who were stunted at 10 years of age (Kanade 1994). Spontaneous or intervention-related catch-up growth during adolescence is discussed in Chapter 2. 3.2.1.3 Stunting and delayed maturation compound risk of adolescent pregnancy Short stature is oftentimes associated with small pelvises in women, and this is an important risk factor for obstructed labour. The risk rises sharply when the stature is below 1.45 m, which is the case of 16- 18% of women in Asia, 11-15% of women in Latin America and 3% in Africa (ACC/SCN 1992a). So maternal stunting is a factor of increased obstetric risk, and it can be attributed to chronic malnutrition, at least in part. In addition, delayed growth and maturation in girls as a result of malnutrition further increases the risks associated with adolescent pregnancy, as biological age lags behind chronological age (see under Section 3.3). 3.2.1.4 Malnutrition reduces work capacity Adolescents’ contribution to agricultural and domestic chores is critical in many populations and it is suspected that undernutrition (and stunting) might limit work capacity and endurance of both boys and girls. The relationship between nutritional status and productivity is complex, as discussed by Kennedy and Garcia (1994), and there have been very few specific studies on adolescents. What is nonetheless suggested by available data from various studies and countries is that BMI, fat free mass and height are associated with increased time devoted to work and with work capacity. Early malnutrition
would affect physical work capacity through an adverse effect on height,body mass and,more specifically, muscle mass.Height in particular has most often been shown to be associated with work output, productivity or income.Usually,when expressed per unit of height or body mass,differences in work capacity were no longer observed,but it is total work output that has practical implications for productive potential,and which may be affected by chronic (or current)malnutrition.However,increased time devoted to work and higher physical work performance are not easily evaluated when a high share is devoted to home production activities,which is more often the case among women than men,whether in adolescence or in adulthood. A prospective study carried out in Guatemala provides new information on chronic effects of early nutrition on physical work capacity in adolescents(Haas et al,1996).The study included an intervention phase of high-energy high-protein supplementation during prenatal life and pre-school years,and a follow-up phase of many years.In the 14-19 year-old cohort males,those having been exposed to early supplementation had a significantly higher oxygen uptake than control subjects at near-exertion levels (VO,max),which provides a measure of physical work capacity.The supplementation effect was not significant in girls,which is attributed to the low levels of physical activity generally seen in girls in this society.The difference observed in males remained significant,although reduced,even after controlling for fat-free mass,which is at variance with previous studies.One suggested explanation,based on experimental data in animals,is that early malnutrition may affect the quality of muscle tissue in terms of fibre type,with an effect on the proportion of fast to low-twitch fibres.However,further research is required to elucidate this effect,as well as to assess better the relationship of physical work capacity with economic productivity.Micronutrient malnutrition,iron deficiency in particular,may also affect work capacity and has to be taken into account in such studies. 3.2.2 Iron deficiency anaemia and other widespread micronutrient deficiencies 3.2.2.1 Iron deficiency and anaemia Anaemia,whether or not the primary cause is iron deficiency,is generally recognized as the main nutritional problem in adolescents.Of 39 studies reviewed by De Maeyer and Adiels-Tegman(1985)on the prevalence of anaemia in adolescents,32 were carried out in developing countries.Estimated prevalence was 27%in developing countries,and 6%in industrialized countries.Results showed that in Africa,Oceania,Latin America and the Caribbean,the prevalence was higher among adolescent boys than girls.In the ICRW/USAID studies(Kurz and Johnson-Welch,1994),anaemia in adolescents was quite high in Nepal(42%),India(55%)one of the two Guatemalan studies(48%)and Cameroon(33%). It was lower in Ecuador (17%)and Jamaica (16%).In rural Guatemala,it was low:5%.These wide variations are not entirely understood,and illustrate how different the problems may be among countries The prevalence was as high in boys as in girls,and it was higher among boys in one study(Ecuador). Because of muscle mass development,boys have high iron requirements,as mentioned earlier,although girls are usually expected to have higher anaemia rates due to onset of menarche.However,as the growth of adolescents slows down,boys'iron status improves.It is not known whether transient anaemia among adolescent boys has functional consequences.Hence,the long-term benefit of intervention in this group is not known.In growing girls,there is a paucity of data on iron requirements,and the consequences of iron deficiency. In Cameroon,prior to a school-based health education programme among adolescents,needs were assessed through KAP(knowledge-attitudes-practices)studies and focus groups with adolescents, literature reviews and workshops(Chendi 1998).Iron deficiency and anaemia were identified as one of the major health and social problems affecting the youth. As reported in a study of iron and zinc status among adolescent girls consuming vegetarian or omnivorous diets in Canada,suboptimal iron and zinc status was the result of intake of poorly available sources of iron and zinc in all dietary groups(Donovan and Gibson,1995).Similarly,iron deficiency and anaemia are reportedly common in British adolescents,especially in girls,with a prevalence of up to 22% hemoglobin (Hb)levels below 120g/l,and 4-43%of low ferritin levels [<10 or 12mg]depending on the NUTRITION IN ADOLES C E N C E /17
NUTRITION IN ADOLESCENCE /17 would affect physical work capacity through an adverse effect on height, body mass and, more specifically, muscle mass. Height in particular has most often been shown to be associated with work output, productivity or income. Usually, when expressed per unit of height or body mass, differences in work capacity were no longer observed, but it is total work output that has practical implications for productive potential, and which may be affected by chronic (or current) malnutrition. However, increased time devoted to work and higher physical work performance are not easily evaluated when a high share is devoted to home production activities, which is more often the case among women than men, whether in adolescence or in adulthood. A prospective study carried out in Guatemala provides new information on chronic effects of early nutrition on physical work capacity in adolescents (Haas et al, 1996). The study included an intervention phase of high-energy high-protein supplementation during prenatal life and pre-school years, and a follow-up phase of many years. In the 14-19 year-old cohort males, those having been exposed to early supplementation had a significantly higher oxygen uptake than control subjects at near-exertion levels (VO2 max), which provides a measure of physical work capacity. The supplementation effect was not significant in girls, which is attributed to the low levels of physical activity generally seen in girls in this society. The difference observed in males remained significant, although reduced, even after controlling for fat-free mass, which is at variance with previous studies. One suggested explanation, based on experimental data in animals, is that early malnutrition may affect the quality of muscle tissue in terms of fibre type, with an effect on the proportion of fast to low-twitch fibres. However, further research is required to elucidate this effect, as well as to assess better the relationship of physical work capacity with economic productivity. Micronutrient malnutrition, iron deficiency in particular, may also affect work capacity and has to be taken into account in such studies. 3.2.2 Iron deficiency anaemia and other widespread micronutrient deficiencies 3.2.2.1 Iron deficiency and anaemia Anaemia, whether or not the primary cause is iron deficiency, is generally recognized as the main nutritional problem in adolescents. Of 39 studies reviewed by De Maeyer and Adiels-Tegman (1985) on the prevalence of anaemia in adolescents, 32 were carried out in developing countries. Estimated prevalence was 27% in developing countries, and 6% in industrialized countries. Results showed that in Africa, Oceania, Latin America and the Caribbean, the prevalence was higher among adolescent boys than girls. In the ICRW/USAID studies (Kurz and Johnson-Welch, 1994), anaemia in adolescents was quite high in Nepal (42%), India (55%) one of the two Guatemalan studies (48%) and Cameroon (33%). It was lower in Ecuador (17%) and Jamaica (16%). In rural Guatemala, it was low: 5%. These wide variations are not entirely understood, and illustrate how different the problems may be among countries. The prevalence was as high in boys as in girls, and it was higher among boys in one study (Ecuador). Because of muscle mass development, boys have high iron requirements, as mentioned earlier, although girls are usually expected to have higher anaemia rates due to onset of menarche. However, as the growth of adolescents slows down, boys’ iron status improves. It is not known whether transient anaemia among adolescent boys has functional consequences. Hence,the long-term benefit of intervention in this group is not known. In growing girls, there is a paucity of data on iron requirements, and the consequences of iron deficiency. In Cameroon, prior to a school-based health education programme among adolescents, needs were assessed through KAP (knowledge-attitudes-practices) studies and focus groups with adolescents, literature reviews and workshops (Chendi 1998). Iron deficiency and anaemia were identified as one of the major health and social problems affecting the youth. Asreported in a study of iron and zinc status among adolescent girls consuming vegetarian or omnivorous diets in Canada, suboptimal iron and zinc status was the result of intake of poorly available sources of iron and zinc in all dietary groups (Donovan and Gibson, 1995). Similarly, iron deficiency and anaemia are reportedly common in British adolescents, especially in girls, with a prevalence of up to 22% hemoglobin (Hb) levels below 120g/l, and 4-43% of low ferritin levels [<10 or 12mg] depending on the
region,ethnic origin,SES,intake,and sampling and analytical methods(Nelson 1996).Low iron intakes alone do not fully account for the high prevalence of anaemia.Other factors such as low vitamin C intakes and some aspects of lifestyle such as dieting for weight loss or untutored adoption of vegetarian diets,were associated with increased risk. Iron requirements of adolescent girls may be further increased because of infections such as malaria, schistosomiasis,and hookworm infection(Brabin and Brabin,1992).Tuberculosis and HIV infection are other etiological factors of iron deficiency(van den Broek and Letsky,1998),and it is known that sexually active adolescents are at increased risk of HIV infection.In Nigeria,Brabin et al(1997)found that adolescent girls who had low Hb(<10g/dl)were more likely to have a low BMI that those who had higher Hb levels,suggesting that overall malnutrition is associated with anaemia Heavy menstrual blood loss may be an important factor of iron deficiency anaemia,as observed in Nigerian girls,and it might also be related to vitamin A deficiency(Barr et al,1998).A 12%menorrhagia rate was found among nulliparous,menstruating girls aged less than 20.Menorrhagia was suspected to be an important contributor to the high rate of anaemia(40%).In a population like this where contraception is desired and culturally acceptable,the authors suggest that contraceptive pills would be the treatment of choice for menorrhagia,while improving iron status. The relationship of geophagy with iron status and anaemia is still obscure.In Kenya,this practice was reported by more than 70%of school children aged 10-18 years,and 56%of pregnant women reported eating soil regularly(Geissler et al,1998a,1998b).Whilst the soil is a potential source of iron,a negative association between iron status and geophagy was found.Either geophagous subjects are deficient to begin with,or soil components interfere with iron uptake or metabolism. Iron deficiency and anaemia may be common among adolescent athletes,owing to chronic urinary and gastrointestinal blood loss and to intravascular hemolysis that are associated with strenuous exercise combined with endurance events(Raunklar and Sabio,1992).It is not known whether heavy physical work which characterizes many poor population groups could contribute to iron deficiency and anaemia among adolescents The consequences of anaemia in terms of poorer pregnancy outcome are well known.In addition to a higher risk oflow birth weight,prematurity,stillbirth,neonatal infection and maternal mortality,anaemia in pregnancy may be associated with a higher risk of hypertension and heart disease in the offspring of anaemic mothers(Barker et al,1990).An inverse association between size at birth and systolic blood pressure in childhood and adult life has also been consistently observed in many studies(Law and Shiell, 1996). Iron deficiency anaemia also reduces physical work capacity,as suggested by positive impact of iron supplementation on work productivity of women tea pickers in Indonesia(see Behrman 1992)and Chinese women working in factories(Liet al,1994).Iron deficiency,even without anaemia,may represent a high loss of productivity in physically demanding work,and in less strenuous labour as well(Ross and Horton,1998).For heavy manual labour,iron therapy in anaemic adults is estimated to result in a 17% increase in work productivity,and this is considered to be a conservative estimate based on existing evidence.To our knowledge,studies on work productivity in relation with iron status were not performed in adolescents,but there is no reason to believe that iron deficiency would not have similar adverse effects among them.Translated in economic terms,the overall productivity loss associated with iron deficiency,including cognitive deficits in children,is about US$4 per capita(Ross and Horton,1998). Iron deficiency has also been shown to reduce endurance among athletes(Raunklar and Sabio,1992). There is evidence of short-term effects of anaemia on performance capacity and recovery from physical activity,as assessed by heart rate,in British adolescent girls from different ethnic backgrounds(Nelson, Bakaliou and Trivedi,1994).If even mild anaemia affects physical activity,it may in the long term affect bone and heart health(Nelson 1996),since it may prevent a healthy pattern of physical activity from being established in adolescence.Risk of osteoporosis and bone fracture is inversely proportional to
18/ region, ethnic origin, SES, intake, and sampling and analytical methods (Nelson 1996). Low iron intakes alone do not fully account for the high prevalence of anaemia. Other factors such as low vitamin C intakes and some aspects of lifestyle such as dieting for weight loss or untutored adoption of vegetarian diets, were associated with increased risk. Iron requirements of adolescent girls may be further increased because of infections such as malaria, schistosomiasis, and hookworm infection (Brabin and Brabin, 1992). Tuberculosis and HIV infection are other etiological factors of iron deficiency (van den Broek and Letsky,1998), and it is known that sexually active adolescents are at increased risk of HIV infection. In Nigeria, Brabin et al (1997) found that adolescent girls who had low Hb (<10g/dl) were more likely to have a low BMI that those who had higher Hb levels, suggesting that overall malnutrition is associated with anaemia. Heavy menstrual blood loss may be an important factor of iron deficiency anaemia, as observed in Nigerian girls, and it might also be related to vitamin A deficiency (Barr et al, 1998). A 12% menorrhagia rate was found among nulliparous, menstruating girls aged less than 20. Menorrhagia was suspected to be an important contributor to the high rate of anaemia (40%). In a population like this where contraception is desired and culturally acceptable, the authors suggest that contraceptive pills would be the treatment of choice for menorrhagia, while improving iron status. The relationship of geophagy with iron status and anaemia is still obscure. In Kenya, this practice was reported by more than 70% of school children aged 10-18 years, and 56% of pregnant women reported eating soil regularly (Geissler et al, 1998a, 1998b). Whilst the soil is a potential source of iron, a negative association between iron status and geophagy was found. Either geophagous subjects are deficient to begin with, or soil components interfere with iron uptake or metabolism. Iron deficiency and anaemia may be common among adolescent athletes, owing to chronic urinary and gastrointestinal blood loss and to intravascular hemolysis that are associated with strenuous exercise combined with endurance events (Raunklar and Sabio, 1992). It is not known whether heavy physical work which characterizes many poor population groups could contribute to iron deficiency and anaemia among adolescents. The consequences of anaemia in terms of poorer pregnancy outcome are well known. In addition to a higher risk of low birth weight, prematurity, stillbirth, neonatal infection and maternal mortality, anaemia in pregnancy may be associated with a higher risk of hypertension and heart disease in the offspring of anaemic mothers (Barker et al, 1990). An inverse association between size at birth and systolic blood pressure in childhood and adult life has also been consistently observed in many studies (Law and Shiell, 1996). Iron deficiency anaemia also reduces physical work capacity, as suggested by positive impact of iron supplementation on work productivity of women tea pickers in Indonesia (see Behrman 1992) and Chinese women working in factories (Li et al, 1994). Iron deficiency, even without anaemia, may represent a high loss of productivity in physically demanding work, and in less strenuous labour as well (Ross and Horton, 1998). For heavy manual labour, iron therapy in anaemic adults is estimated to result in a 17% increase in work productivity, and this is considered to be a conservative estimate based on existing evidence. To our knowledge, studies on work productivity in relation with iron status were not performed in adolescents, but there is no reason to believe that iron deficiency would not have similar adverse effects among them. Translated in economic terms, the overall productivity loss associated with iron deficiency, including cognitive deficits in children, is about US$4 per capita (Ross and Horton, 1998). Iron deficiency has also been shown to reduce endurance among athletes (Raunklar and Sabio, 1992). There is evidence of short-term effects of anaemia on performance capacity and recovery from physical activity, as assessed by heart rate, in British adolescent girls from different ethnic backgrounds (Nelson, Bakaliou and Trivedi, 1994). If even mild anaemia affects physical activity, it may in the long term affect bone and heart health (Nelson 1996), since it may prevent a healthy pattern of physical activity from being established in adolescence. Risk of osteoporosis and bone fracture is inversely proportional to
exercise levels,and activity levels in adolescence may be reflected in activity levels at middle age.Similarly, physical activity is a protective factor in relation to heart disease. Iron deficiency may alter cognitive function in children(Pollitt et al,1985)and even in adolescents (Ballin et al,1992)and the effects may be only partly reversible in severe and prolonged deficiency. Effects on cognition beyond childhood are less well documented and understood however,although improvements in cognitive tests following iron supplementation were reported among adolescents in south and south-east Asia,but not in the United Kingdom(Nelson 1996).In population groups with a high rate of anaemia,this nutritional problem may contribute to poor levels of school achievement, along with social and other environmental factors.In a study among adolescent schoolgirls(13-14 years of age)of low SES in Jamaica(Walker et al,1994;1996),anaemia was identified as the principal nutritional problem,affecting 16%of the girls.Height for age,hemoglobin level,and reported hunger episodes were significantly correlated with school achievement.Anaemia remained significant when controlling for social factors and school attendance,although social and behavioural factors may be more significant determinants of school performance in adolescence than in earlier years.For instance,it was found that having many household chores to do before going to school affected the girls'school attendance and, through this,their achievement. The role of iron deficiency(and perhaps also folate)in depressing physical growth,as suggested in studies on supplemented pregnant adolescents,has been referred to earlier(see Chapter 2). In the USA,the second National Health and Nutrition Examination Survey(NHANES II)results indicated that anaemia occurred in 5%of males aged 11-14 and approximately 2.5%of females aged 11-19(Expert Scientific Working Group,1985).For the higher prevalence in boys,which is also observed in developing countries,the only explanation proposed was poorer dietary habits. Clinical data do not support the suggestion that iron deficiency protects against infection,or that correction ofiron deficiency increases the severity of infectious disease(Chandra 1991),or the prevalence of malaria (Menendez et al,1994). Iron deficiency is related to vitamin A status.Many studies suggest a direct interaction between vitamin A status and the utilization of dietary and stored iron for hemoglobin formation(Bloem et al,1989; Meija 1992;Ahmed et al,1993).Among urban adolescent schoolgirls in Bangladesh,probably a more affluent segment of the population,the rate of anaemia was 22%based on Hb<120g/l(Ahmed et al, 1996).Other biochemical findings were indicative of iron deficiency anaemia.The girls with the lowest retinol level were found to have lower values for Hb and other biochemical indices including serum iron and transferrin saturation,even after adjustments were made for potentially confounding socio- demographic factors.This again suggests that vitamin A deficiency may have contributed to the aetiology of iron deficiency anaemia.Thus,marginal vitamin A status may compromise iron metabolism.This is of particular concern in adolescent pregnancy.Furthermore,some studies suggest that menstrual irregularities may be more frequent in women with low vitamin A stores or serum retinol (Barr et al, 1998).For Brabin and Brabin(1992),the associations of both vitamin A and iron with menstrual blood loss suggest the need for controlled studies on the range of blood loss in chronically malnourished adolescent girls.Similarly,they see the need for baseline data on vitamin A deficiency,anaemia and menstrual disorders in young women,in order to assess the relative importance of nutritional status for reproductive health in developed and developing countries. In Malawi,it was reported that a high proportion of rural non-pregnant adolescent girls were anaemic (only 11%had Hb equal or greater than 12 g/dl)and deficient in vitamin A(27%had serum retinol <0.7 mmol/L and 40%had low vitamin A stores according to the modified relative dose response test (MRDR)and vitamin E,although the precise significance of the latter is as yet unclear(Fazio-Tirrozzo et al,1998).Younger girls were more likely to have a marginal vitamin A status than older ones.Among the primiparous adolescents,74%had serum retinol <0.7 mmol/L.The authors advocate vitamin A supplementation among adolescents,or else extended supplementation in schools up to 12 years,but this would hardly be sustainable in Malawi since school attendance is so low. NUTRITION IN ADOLES C E N C E /19
NUTRITION IN ADOLESCENCE /19 exercise levels, and activity levels in adolescence may be reflected in activity levels at middle age. Similarly, physical activity is a protective factor in relation to heart disease. Iron deficiency may alter cognitive function in children (Pollitt et al, 1985) and even in adolescents (Ballin et al, 1992) and the effects may be only partly reversible in severe and prolonged deficiency. Effects on cognition beyond childhood are less well documented and understood however, although improvements in cognitive tests following iron supplementation were reported among adolescents in south and south-east Asia, but not in the United Kingdom (Nelson 1996). In population groups with a high rate of anaemia, this nutritional problem may contribute to poor levels of school achievement, along with social and other environmental factors. In a study among adolescent schoolgirls (13-14 years of age) of low SES in Jamaica (Walker et al, 1994; 1996), anaemia was identified as the principal nutritional problem, affecting 16% of the girls. Height for age, hemoglobin level, and reported hunger episodes were significantly correlated with school achievement. Anaemia remained significant when controlling for social factors and school attendance, although social and behavioural factors may be more significant determinants of school performance in adolescence than in earlier years. For instance, it was found that having many household chores to do before going to school affected the girls’ school attendance and, through this, their achievement. The role of iron deficiency (and perhaps also folate) in depressing physical growth, as suggested in studies on supplemented pregnant adolescents, has been referred to earlier (see Chapter 2). In the USA, the second National Health and Nutrition Examination Survey (NHANES II) results indicated that anaemia occurred in 5% of males aged 11-14 and approximately 2.5% of females aged 11-19 (Expert Scientific Working Group, 1985). For the higher prevalence in boys, which is also observed in developing countries, the only explanation proposed was poorer dietary habits. Clinical data do not support the suggestion that iron deficiency protects against infection, or that correction of iron deficiency increases the severity of infectious disease (Chandra 1991), or the prevalence of malaria (Menendez et al, 1994). Iron deficiency is related to vitamin A status. Many studies suggest a direct interaction between vitamin A status and the utilization of dietary and stored iron for hemoglobin formation (Bloem et al, 1989; Meija 1992; Ahmed et al, 1993). Among urban adolescent schoolgirls in Bangladesh, probably a more affluent segment of the population, the rate of anaemia was 22% based on Hb<120g/l (Ahmed et al, 1996). Other biochemical findings were indicative of iron deficiency anaemia. The girls with the lowest retinol level were found to have lower values for Hb and other biochemical indices including serum iron and transferrin saturation, even after adjustments were made for potentially confounding sociodemographic factors. This again suggests that vitamin A deficiency may have contributed to the aetiology of iron deficiency anaemia. Thus, marginal vitamin A status may compromise iron metabolism. This is of particular concern in adolescent pregnancy. Furthermore, some studies suggest that menstrual irregularities may be more frequent in women with low vitamin A stores or serum retinol (Barr et al, 1998). For Brabin and Brabin (1992), the associations of both vitamin A and iron with menstrual blood loss suggest the need for controlled studies on the range of blood loss in chronically malnourished adolescent girls. Similarly, they see the need for baseline data on vitamin A deficiency, anaemia and menstrual disorders in young women, in order to assess the relative importance of nutritional status for reproductive health in developed and developing countries. In Malawi, it was reported that a high proportion of rural non-pregnant adolescent girls were anaemic (only 11% had Hb equal or greater than 12 g/dl) and deficient in vitamin A (27% had serum retinol <0.7 mmol/L and 40% had low vitamin A stores according to the modified relative dose response test (MRDR) and vitamin E, although the precise significance of the latter is as yet unclear (Fazio-Tirrozzo et al, 1998). Younger girls were more likely to have a marginal vitamin A status than older ones. Among the primiparous adolescents, 74% had serum retinol <0.7 mmol/L. The authors advocate vitamin A supplementation among adolescents, or else extended supplementation in schools up to 12 years, but this would hardly be sustainable in Malawi since school attendance is so low
3.2.2.2 Vitamin A deficiency Although the risk of vitamin A deficiency tends to decline with age,it is now apparent that it often extends in adolescence and early adulthood(Henning et al,1991),especially among women(Bloem et al,1995).Evidence of high deficiency rates in adolescents in Bangladesh and Malawi was just described. In adolescent female factory workers in Bangladesh(Ahmed et al,1997),it was found that 56.2%had low serum retinol (<1.05 mmol)and 14.2%were deficient (serum retinol <0.7 mmol/l).After adjusting for potential confounders,it was found that serum retinol was significantly higher in girls who consumed milk and dark green leafy vegetables more frequently.Here again,serum retinol and Hb were correlated. Nearly half(44%)were anaemic,which is twice as high as in upper-level-school adolescent girls(Ahmed et al,1996).These girls were not wasted,however. In Cameroon,the study on adolescents(Kurz and Som,1998)revealed that vitamin A intakes were extremely low.This again suggests that vitamin A deficiency in adolescence may be of particular concern. Very few studies have investigated the relationship of specific nutrients with delayed and catch-up growth in adolescents.As noted above,iron,and possibly folate,may be involved in adolescent growth(Harrison et al,1985).Based on existing data,Brabin and Brabin(1992)hypothesize that iron and vitamin A requirements are increased for growth in adolescence and that deficiencies may be a consequence of growth on marginal diets among adolescent girls.The relationship of serum retinol binding protein and retinol with puberty level suggests an important role of vitamin A in sexual maturation (Herbeth et al,1991) 3.2.2.3 Todine deficiency disorders lodine deficiency disorders were widely prevalent in most populations until corrective measures were taken.Neuromotor and cognitive impairments of variable degrees are the most important consequences of iodine deficiency(Stanbury 1998).lodine deficiency is recognized as the most common cause of preventable mental retardation in the world.Cretinism is only the extreme end of the spectrum.In iodine-deficiency areas,a downward shift of IQs has been reported(Bleichrodt et al,1989),as well as lower performance in school after controlling for confounding variables(Fierro-Benitez et al,1986).In India,a study compared learning and motivation in male schoolchildren aged 9-15 years from severely iodine-deficient villages and from mildly iodine-deficient villages,after matching the groups for age, SES and formal education(Tiwari et al,1996).The results suggested that children from severely deficient villages not only suffered neural impairment,but also lacked socio-psychological stimulation in the endemic sites,which explained learning disability,as well as low motivation to perform.Foetal and pre- and postnatal survival is markedly affected by iodine deficiency,as strongly suggested by a doubling of neonatal survival following correction of the deficiency in Chinese communities(De Long et al,1997). Thus,iodine deficiency,because of its lasting effects on survival and intellectual achievements,is a major obstacle to social and economic development.Iodine deficiency affects all age groups,but goitre primarily affects people aged 15-45 years,in particular women,as shown for example in Cote d'Ivoire(Kouame et al,1998).There are rare instances of endemic goitre in the absence of iodine deficiency,like in one province of South Africa(Jooste et al,1999).This is not entirely explained,but high fluoride content of drinking water and dietary goitrogens may be involved. Control of iodine deficiency is imperative,considering the dramatic repercussions on neonatal mortality and mental development,and it is well under way (see Chapter 4).Understandably,women of reproductive age are a priority target group for intervention.Iodine deficiency is assessed by goitre and urinary iodine levels among schoolchildren,as these are captive groups.Some adolescents are'captured in these surveys,but evaluation or surveillance data are not reported separately for this group. 3.2.2.4 Micronutrient deficiencies and bone disease Calcium requirements for skeletal development appear to be even greater during adolescence than childhood or young adulthood(Matkovic and Ilich,1993).Because maximum bone mass is acquired 20/
20/ 3.2.2.2 Vitamin A deficiency Although the risk of vitamin A deficiency tends to decline with age, it is now apparent that it often extends in adolescence and early adulthood (Henning et al, 1991), especially among women (Bloem et al, 1995). Evidence of high deficiency rates in adolescents in Bangladesh and Malawi was just described. In adolescent female factory workers in Bangladesh (Ahmed et al, 1997), it was found that 56.2% had low serum retinol (<1.05 mmol) and 14.2% were deficient (serum retinol <0.7 mmol/l). After adjusting for potential confounders, it was found that serum retinol was significantly higher in girls who consumed milk and dark green leafy vegetables more frequently. Here again, serum retinol and Hb were correlated. Nearly half (44%) were anaemic, which is twice as high as in upper-level-school adolescent girls (Ahmed et al, 1996). These girls were not wasted, however. In Cameroon, the study on adolescents (Kurz and Som, 1998) revealed that vitamin A intakes were extremely low. This again suggests that vitamin A deficiency in adolescence may be of particular concern. Very few studies have investigated the relationship of specific nutrients with delayed and catch-up growth in adolescents. As noted above, iron, and possibly folate, may be involved in adolescent growth (Harrison et al, 1985). Based on existing data, Brabin and Brabin (1992) hypothesize that iron and vitamin A requirements are increased for growth in adolescence and that deficiencies may be a consequence of growth on marginal diets among adolescent girls. The relationship of serum retinol binding protein and retinol with puberty level suggests an important role of vitamin A in sexual maturation (Herbeth et al, 1991). 3.2.2.3 Iodine deficiency disorders Iodine deficiency disorders were widely prevalent in most populations until corrective measures were taken. Neuromotor and cognitive impairments of variable degrees are the most important consequences of iodine deficiency (Stanbury 1998). Iodine deficiency is recognized as the most common cause of preventable mental retardation in the world. Cretinism is only the extreme end of the spectrum. In iodine-deficiency areas, a downward shift of IQs has been reported (Bleichrodt et al, 1989), as well as lower performance in school after controlling for confounding variables (Fierro-Benitez et al, 1986). In India, a study compared learning and motivation in male schoolchildren aged 9-15 years from severely iodine-deficient villages and from mildly iodine-deficient villages, after matching the groups for age, SES and formal education (Tiwari et al, 1996). The results suggested that children from severely deficient villages not only suffered neural impairment, but also lacked socio-psychological stimulation in the endemic sites, which explained learning disability, as well as low motivation to perform. Foetal and preand postnatal survival is markedly affected by iodine deficiency, as strongly suggested by a doubling of neonatal survival following correction of the deficiency in Chinese communities (De Long et al, 1997). Thus, iodine deficiency, because of its lasting effects on survival and intellectual achievements, is a major obstacle to social and economic development. Iodine deficiency affects all age groups, but goitre primarily affects people aged 15-45 years, in particular women, as shown for example in Côte d’Ivoire (Kouame et al, 1998). There are rare instances of endemic goitre in the absence of iodine deficiency, like in one province of South Africa (Jooste et al, 1999). This is not entirely explained, but high fluoride content of drinking water and dietary goitrogens may be involved. Control of iodine deficiency is imperative, considering the dramatic repercussions on neonatal mortality and mental development, and it is well under way (see Chapter 4). Understandably, women of reproductive age are a priority target group for intervention. Iodine deficiency is assessed by goitre and urinary iodine levels among schoolchildren, as these are captive groups. Some adolescents are ‘captured’ in these surveys, but evaluation or surveillance data are not reported separately for this group. 3.2.2.4 Micronutrient deficiencies and bone disease Calcium requirements for skeletal development appear to be even greater during adolescence than childhood or young adulthood (Matkovic and Ilich, 1993). Because maximum bone mass is acquired