Ultrasound measurement of fetal size in rural Guatemala

OBJECTIVES

To describe the fetal growth pattern of a population from rural Guatemala and determine when during gestation growth faltering becomes evident.

METHODS

Ultrasound examinations were conducted for 319 women. Femur length (FL), biparietal diameter (BPD), abdominal (AC) and head circumference (HC) were compared with reference values.

RESULTS

FL and AC were similar to reference values throughout gestation. BPD and HC were below the 50th percentile by 30 weeks' gestation and below the 10th percentile later in gestation. We expected all four dimensions to show marked growth restriction during gestation. Measurement differences may explain the results but would call into question the value of cross-study comparisons. Infants born small for gestational age were small in all measures as early as 15 weeks.

CONCLUSIONS

Fetal growth faltering begins in early gestation among infants who were born small. The lack of deviation from reference data for FL and AC requires further clarification.

Iron deficiency and reduced work capacity: a critical review of the research to determine a causal relationship

The causal relationship between iron deficiency and physical work capacity is evaluated through a systematic review of the research literature, including animal and human studies. Iron deficiency was examined along a continuum from severe iron-deficiency anemia (SIDA) to moderate iron-deficiency anemia (MIDA) to iron deficiency without anemia (IDNA). Work capacity was assessed by aerobic capacity, endurance, energetic efficiency, voluntary activity and work productivity. The 29 research reports examined demonstrated a strong causal effect of SIDA and MIDA on aerobic capacity in animals and humans. The presumed mechanism for this effect is the reduced oxygen transport associated with anemia; tissue iron deficiency may also play a role through reduced cellular oxidative capacity. Endurance capacity was also compromised in SIDA and MIDA, but the strong mediating effects of poor cellular oxidative capacity observed in animals have not been demonstrated in humans. Energetic efficiency was affected at all levels of iron deficiency in humans, in the laboratory and the field. The reduced work productivity observed in field studies is likely due to anemia and reduced oxygen transport. The social and economic consequences of iron-deficiency anemia (IDA) and IDNA have yet to be elucidated. The biological mechanisms for the effect of IDA on work capacity are sufficiently strong to justify interventions to improve iron status as a means of enhancing human capital. This may also extend to the segment of the population experiencing IDNA in whom the effects on work capacity may be more subtle, but the number of individuals thus affected may be considerably more than those experiencing IDA.

Higher arterial oxygen saturation during submaximal exercise in Bolivian Aymara compared to European sojourners and Europeans born and raised at high altitude

Arterial oxygen saturation (SaO(2)) was measured at 3,600-3,850 m by pulse oximetry at rest and during submaximal exercise in three study groups: 1) highland Aymara natives of the Bolivian altiplano (n = 25); 2) lowland European/North American sojourners to the highlands with at least 2 months of acclimatization time to 3,600 m (n = 27); and 3) subjects of European ancestry born and raised at 3,600 m (n = 22). Aymara subjects maintained approximately 1 percentage point higher SaO(2) during submaximal work up to 70% of their maximal work capacity, and showed a smaller rate of decline in SaO(2) with increasing work compared to both European study groups. The higher-exercise SaO(2) of Aymara compared to Europeans born and raised at 3,600 m suggests genetic adaptation. The two European study groups, who differed by exposure to high altitude during their growth and development period, did not show any significant difference in either resting or exercise SaO(2). This suggests that the developmental mode of adaptation is less important than the genetic mode of adaptation in determining exercise SaO(2). A weak correlation was detected (across study groups only) between the residual forced vital capacity (FVC) and the residual SaO(2) measured at the highest level of submaximal work output (P = 0.024, R = 0.26). While firm conclusions based on this correlation are problematic, it is suggested that a part of the higher SaO(2) observed in Aymara natives is due to a larger lung volume and pulmonary diffusion capacity for oxygen. Results from this study are compared to similar studies conducted with Tibetan natives, and are interpreted in light of recent quantitative genetic analyses conducted in both the Andes and Himalayas.

Iron supplementation improves endurance after training in iron-depleted, nonanemic women

Our objective was to investigate the effects of iron depletion on adaptation to aerobic exercise, assessed by time to complete a 15-km cycle ergometer test. Forty-two iron-depleted (serum ferritin <16 microg/l), nonanemic (Hb >12 g/dl) women (18-33 yr old) received 100 mg of ferrous sulfate (S) or placebo (P) per day for 6 wk in a randomized, double-blind trial. Subjects trained for 30 min/day, 5 days/wk at 75-85% of maximum heart rate for the final 4 wk of the study. There were no group differences in baseline iron status or in 15-km time. Iron supplementation increased serum ferritin and decreased transferrin receptors in the S compared with the P group. The S and P groups decreased 15-km time and respiratory exchange ratio and increased work rate during the 15-km time trial after training. The decrease in 15-km time was greater in the S than in the P group (P = 0.04) and could be partially attributed to increases in serum ferritin and Hb. These results indicate that iron deficiency without anemia impairs favorable adaptation to aerobic exercise.

Effect of developmental and ancestral high-altitude exposure on VO(2)peak of Andean and European/North American natives

Peak oxygen consumption (VO(2)peak) was measured in 150 adult males (18-35 years old) in Bolivia, using a complete migrant study design to partition developmental from ancestral (genetic) effects of high-altitude (HA) exposure. High-altitude natives (HANs, Aymara/Quechua ancestry, n = 75) and low-altitude natives (LANs, European/North American ancestry, n = 75) were studied at high altitude (3,600-3,850 m) and near sea level (420 m). HAN and LAN migrant groups to a nonnative environment were classified as: multigeneration migrants, born and raised in a nonnative environment; child migrants who migrated to the nonnative environment during the period of growth and development (0-18 years old); and adult migrants who migrated after 18 years of age. Variability in VO(2)peak due to high-altitude adaptation was modeled by covariance analysis, adjusting for fat-free mass and physical activity (training) differences between groups. A trend for increased VO(2)peak with increasing developmental high-altitude exposure in migrant groups did not reach statistical significance, but low statistical power may have limited the ability to detect this effect. HANs and LANs born, raised, and tested at high altitude had similar VO(2)peak values, indicating no genetic effect, or an effect much smaller than that reported previously in the literature. There was no functional correlation between forced vital capacity and VO(2)peak, within or across groups. These results do not support the hypothesis that Andean HANs have been selected to express a greater physical work capacity in hypoxia.

Hemoglobin correction factors for estimating the prevalence of iron deficiency anemia in pregnant women residing at high altitudes in Bolivia

This study had two primary objectives: 1) to derive a method to determine hemoglobin cutoffs that could be used to better estimate the prevalence of iron deficiency anemia in pregnancy at high altitudes and 2) to estimate the prevalence of anemia in a sample of pregnant women residing in two cities in Bolivia, La Paz (3,600 meters) and El Alto (4,000 meters). We derived a hemoglobin-altitude curve from previously published data on the mean hemoglobin concentrations of nonanemic women of childbearing age at various altitudes. In addition, we abstracted data on hemoglobin concentration during pregnancy from medical records of women from La Paz and El Alto who had given birth at a maternity hospital in La Paz between January and June of 1996. Using our approach and two other previously published, currently used methods, we calculated and compared prevalences of iron deficiency anemia in this population using hemoglobin cutoffs determined from a hemoglobin-altitude curve corrected for pregnancy. The hemoglobin-altitude curve derived in this study provided a better fit to data for women of childbearing age than the two other models. Those models used cutoffs based on non-iron-replete populations of children or men, both of which were residing below 4,000 m, and then extrapolated to women and higher altitudes. The estimated prevalences of iron deficiency anemia in pregnancy using the hemoglobin cutoffs determined in this study were higher than those estimated by the two other approaches.

The comparison of mixed distribution analysis with a three-criteria model as a method for estimating the prevalence of iron deficiency anaemia in Costa Rican children aged 12-23 months

BACKGROUND

A maximum likelihood method of mixed distribution analysis (MDA) is presented as a method to estimate the prevalence of iron deficiency anaemia (IDA) in Costa Rican infants 12-23 months old. MDA characterizes the parameters of the admixed distributions of iron deficient anaemics and non-iron-deficient-anaemics (NA) from the frequency distribution of haemoglobin concentration of the total sample population.

METHODS

Data collected by Lozoff et al. (1986) from 345 Costa Rican infants 12-23 months old were used to estimate the parameters of the IDA and NA haemoglobin distributions determined by MDA and the widely used three-criteria model of iron deficiency. The estimates of the prevalence of IDA by each of the methods were compared. The sensitivity and specificity of MDA compared to diagnosis by the three-criteria method were assessed. Simulations were carried out to assess the comparability of MDA and the three-criteria method in low and high prevalence scenarios.

RESULTS

The mean and standard deviation (SD) of the NA haemoglobin distribution determined by both methods was 12.1 +/- 1.0 g/dL. The IDA haemoglobin distribution determined by MDA had a mean and SD of 10.2 +/- 1.3 g/dL while the IDA distribution by the three-criteria method had a mean and SD of 10.4 +/- 1.3 g/dL. The prevalences of IDA as estimated by MDA and the three-criteria method were 24% and 29%, respectively. The sensitivity and specificity of MDA were 95% and 97%, respectively. The performance of MDA was similar to the three-criteria method at a simulated high prevalence of IDA and less similar at a low prevalence of IDA.

CONCLUSIONS

Compared to the reference three-criteria method MDA provides a more accurate estimate of the true prevalence of IDA than the haemoglobin cutoff method in a population of children aged 12-23 months with a moderate to high prevalence of IDA. MDA is a less costly method for estimating the severity of IDA in populations with moderate to high prevalences of IDA, and for assisting in the design, monitoring and evaluation of iron intervention programmes.

Altered metabolic response of iron-depleted nonanemic women during a 15-km time trial

In this double-blinded study, 37 women with iron depletion without anemia (age 19-36 yr) were randomly assigned to receive either an iron supplement (135 mg/day) or a placebo. Endurance capacity was assessed during a 15-km simulated time trial (TT) on a cycle ergometer before and after the 8-wk treatment. After the treatment, although the iron-supplemented group did not have shorter time to finish the TT (time), it had 2.0 kJ/min lower energy expenditure and 5.1% lower fractional utilization of peak oxygen consumption during the TT compared with the placebo group, after controlling for work rate (P < 0.05). Time, fractional utilization of peak oxygen consumption, and plasma lactate concentration at the 5th km of the TT were all negatively associated with hemoglobin levels, after controlling for work rate (P < 0.05). In conclusion, repletion of iron stores to women with iron depletion without anemia increased their energetic efficiency, and oxygen transport capacity of the blood was found to be an important determinant of endurance capacity and energy metabolism in nonanemic women.

Response of serum transferrin receptor to iron supplementation in iron-depleted, nonanemic women

Serum transferrin receptor (sTfR) concentration has been recognized recently as a reliable indicator of functional iron deficiency, but its response to iron supplementation has not been investigated in marginally iron-deficient women. In this randomized, double-blinded trial, 37 female subjects aged 19-35 y with iron depletion without anemia (hemoglobin > 120 g/L and serum ferritin < 16 microg/L) received an iron supplement or placebo for 8 wk. Iron status was measured before treatment, after 4 wk of treatment, and posttreatment (ie, after 8 wk of treatment). Iron supplementation of these iron-depleted, nonanemic women resulted in a progressive and significant decrease in sTfR and a significant increase in serum ferritin, and prevented a fall in hemoglobin. The responsiveness of sTfR to iron treatment indicated that sTfR is a sensitive indicator of marginal iron deficiency in iron-depleted, nonanemic women, even when their body iron stores were being replenished.

Iron depletion without anemia and physical performance in young women

Studies in laboratory animals found that iron deficiency without anemia decreased oxidative capacity and increased reliance on carbohydrate as the substrate for energy, thereby causing impaired endurance. The purpose of this cross-sectional study was to investigate the relation between iron deficiency without anemia and physical performance in healthy active women aged 19-36 y. Iron-status assessment included determination of hemoglobin, hematocrit, transferrin saturation, and serum ferritin values. Dietary iron intake was assessed by frequency questionnaires and physical activity level was estimated by frequency questionnaires and 2-wk records. Fifteen women with normal iron status and 15 women with iron depletion (serum ferritin < 12 micrograms/L) were chosen randomly from a group of 69 nonanemic women and given physical-performance tests, including determinations of maximum oxygen consumption (VO2max), ventilatory threshold, and delta-efficiency. There were no significant differences between the two groups in body size, body composition, physical activity level, dietary iron intake, delta-efficiency, or ventilatory threshold. Compared with the iron-depleted group, the iron-sufficient group had significantly higher hemoglobin, transferrin saturation, and serum ferritin values and a significantly greater tendency to use iron supplements. When physical activity level and fat-free mass were controlled for, the iron-depleted group had a significantly lower VO2max. The difference in VO2max was significantly associated with serum ferritin concentration; hemoglobin value was not a significant confounder. Therefore, reduction of VO2max in nonanemic women with iron depletion was likely caused by factors related to reduced body iron storage but was unrelated to decreased oxygen-transport capacity of the blood.

Evidence of a role for fat-free body mass in modulation of plasma carotenoid concentrations in older men: studies with hydrodensitometry

We examined the relationship between body composition and changes in plasma carotenoid concentration in response to dietary carotenoid restriction or beta-carotene (betaC) supplementation in healthy older men. Subjects (mean age 65 y) were assigned randomly to supplement (30 mg betaC/d) or placebo groups, and all subjects consumed a standard low carotenoid basal diet plus 1.5 mg betaC/d as carrots. Body composition was measured at baseline by hydrodensitometry, and plasma carotenoids were measured at baseline and after 28 d of treatment by HPLC. Baseline plasma total carotenoid concentration was significantly and negatively correlated with body mass index (BMI) and fat-free mass (FFM) but not with fat mass, whereas baseline betaC concentration was negatively associated with all three variables. The increase in plasma betaC concentration in response to betaC supplementation was significantly and inversely correlated with BMI and FFM but not with fat mass. Likewise, the decline in plasma total carotenoid concentration in the placebo group was also significantly and inversely related to BMI and FFM but not to fat mass. Thus, FFM seems to be an important determinant of plasma carotenoid concentrations and to explain a substantial portion of the often-observed relationship between BMI and blood carotenoid levels. Fat-free mass seems to represent a dynamic reservoir that dampens short-term changes in plasma carotenoid concentrations during fluctuation in carotenoid intake.

Early nutritional supplementation and skeletal maturation in Guatemalan adolescents

The effect of early childhood nutritional supplementation on skeletal maturation at adolescence was investigated in 663 rural Guatemalans, aged 11-18 y. Skeletal maturation was assessed by the Tanner-Whitehouse-2 method. The subjects were former participants in the Institute of Nutrition of Central America and Panama longitudinal study of growth and development (1969-77) residing in four villages (two large and two small) in eastern Guatemala. The villages were randomized within pairs to receive either a high energy, high protein supplement (Atole) or a low energy supplement with no protein (Fresco). Skeletal maturity was observed across all villages to be delayed significantly relative to a British reference for boys < 14 y of age, but not for older boys or for girls < 14 y of age. Delays in girls > 14 years could not be determined reliably because many had reached maturity. Girls < 14 years from Atole villages were more advanced in skeletal maturity than similar age girls from Fresco villages but these differences were found only in comparisons of the large villages. The relationship between early nutrition and biological maturation at adolescence may be obscured in this sample by the advanced age at which the subjects were examined in adolescence.

Nutritional supplementation during the preschool years and physical work capacity in adolescent and young adult Guatemalans

A follow-up study (1988-89) was carried out in 364 rural Guatemalans, 11-27 y of age, who earlier had participated in a nutritional supplementation experiment. Among its objectives was the assessment of the long-term effects of the nutrition intervention on physical work capacity. Subjects and their mothers from two villages had available a high-energy, high-protein supplement (Atole: 163 kcal/682 kJ and 6.4 g protein per serving or 180 mL), whereas in two other villages a low-energy, no-protein supplement (Fresco: 59 kcal/247 kJ per 180 mL) was provided. Consumption was ad libitum. Maximum oxygen consumption (VO2max) at follow-up was significantly greater in Atole compared with Fresco subjects of both sexes. In subjects 14-19 y, exposed to supplementation throughout gestation and the first 3 y of life, Atole males had a significantly higher VO2max (2.62 L/min) than Fresco males (2.24 L/min), the differences remaining significant even after controlling for body weight and fat-free mass; also, there was a significant positive relationship between amount of supplement consumed and VO2max. The supplementation effect in females of similar age was not statistically significant. It is concluded that early nutritional improvements can have long-lasting effects on physical performance.

Nutritional supplementation during the preschool years influences body size and composition of Guatemalan adolescents

Effects of supplementary feeding during early childhood on body size and composition at adolescence are examined in a population with marked growth failure in the first 3 y of life. The data came from a supplementation trial conducted in rural Guatemala from 1969 to 1977 and a 1988-89 follow-up study of the same subjects at adolescence. Two pairs of villages participated in the trial. One village from each pair received a high protein-energy supplement (Atole), which significantly improved dietary intakes, whereas the other village of the pair received a low-energy, no-protein supplement (Fresco), which did not impact appreciably on dietary intakes. Children from Atole villages grew better during the preschool period than children from Fresco villages. At adolescence, subjects from Atole villages were taller, weighed more and had greater fat-free masses than subjects from Fresco villages. Differences in height at adolescence were slightly reduced in magnitude relative to differences at 3 y of age. However, differences in weight were increased in adolescence relative to 3 y of age.

Overweight schoolchildren in New York State: prevalence and characteristics

OBJECTIVES

Childhood overweight is an increasing public health concern. This study was undertaken to determine the prevalence of overweight in elementary school children in New York State and to identify characteristics associated with child fatness.

METHODS

Weight, height, triceps skinfold, midarm circumference, and a 24-hour dietary recall were taken on 1797 second- and fifth-grade students from 51 randomly selected schools in New York State outside of New York City. Parents completed a brief questionnaire.

RESULTS

In comparison with 1974 and 1980 national reference data, up to twice the expected percentages of children had values above the 85th, 90th, and 95th percentiles for body mass index, triceps skinfold, and arm fat area. Regression analyses suggested that children who tended to be fatter were members of low socioeconomic status, two-parent (but not single-parent) households; those with few or no siblings; those who ate school lunch; and those who skipped breakfast.

CONCLUSIONS

The findings suggest that overweight is a problem among many elementary school children in New York State and that sociodemographic characteristics may be useful for targeting preventive efforts.

Testing the effects of nutrient deficiencies on behavioral performance

The association between specific nutrient deficiencies and poor performance on behavioral tests has been documented for several nutrients. The determination of causality, however, remains elusive. This paper presents the essential criteria for a valid test of causality. Findings from experimental studies in which a nutritional treatment was randomly allocated can be summarized in a statistical statement about the probability that the nutrient treatment caused the behavioral response. Criteria for assessing the internal validity of these studies are examined in terms of whether alleviation of a nutrient deficiency did or did not produce a detectable behavioral response. The plausibility of such a causal inference is dependent on its congruency with known or theorized biological and behavioral mechanisms. External validity describes the extent to which inferences from internally valid studies may be applicable to other populations or circumstances. In addition to these scientific considerations, some of the ethical issues of nutrient-treatment trials are also discussed. All of these considerations provide a better basis for judging whether public health action would be worthwhile than do observed associations that could actually be due to other causes.

Serum alkaline phosphatase activity and skeletal maturation in Guatemalan adolescents

Serum alkaline phosphatase activity (AP), stature and Tanner-Whitehouse-2 RUS skeletal age (SA) were determined for 873 rural Guatemalan youth and young adults 11-25 years of age. Mean AP decreases systematically with chronological age (CA) in girls, while an adolescent increase in mean AP occurs at 14 years in boys. When mean AP is calculated within SA groups, clear adolescent increases are apparent in girls, peaking at 11 years SA, and at 14 years SA in boys. Correlations between AP and relative skeletal age (SA-CA) decrease systematically from moderately positive at the youngest CA groups to moderately negative at the older ages, crossing zero at the chronological ages of maximum adolescent AP values. Analyses suggest the patterns of mean AP in adolescence follow closely the timing and patterns of growth velocity in stature in each sex, and are only indirectly related to SA as it is a proxy for the maturational timing of the adolescent spurt in stature.

Predicting body composition from anthropometry and bioimpedance in marginally undernourished adolescents and young adults

Body-composition prediction equations were developed using data from a sample of 201 female and male Guatemalan ladinos (ie, people of Amerindian-European descent) aged 11-25 y. Fat-free mass (FFM) values were estimated from body density by using the two-component model and age- and sex-specific values for the density of FFM. The root-mean-square error (RMSE) of the best model predicting FFM from a set of simple anthropometric variables was 1.59 kg for females and 1.90 kg for males. The addition of more extensive anthropometry to the set of candidate predictors reduced the RMSE to 1.42 kg for females and 1.88 kg for males. The subsequent addition of a bioelectrical impedance measure (Ht2/R) further reduced the RMSE to 1.32 kg for females and 1.82 kg for males. These results suggest that for a marginally undernourished population with relatively little body fat, simple anthropometrics are as useful as more sophisticated measures for the prediction of body composition.

Differences in early postnatal morbidity risk by pattern of fetal growth in Argentina

Information on a cohort of 5539 singleton births delivered at term in two hospitals in Rosario, Argentina, was used to examine differences in early postnatal morbidity between small for gestational age (SGA) infants classified by their ponderal index (PI). SGA infants with low PI (SGA-LPI) were 4.35 (90% CI: 1.50, 12.61) times more likely to have asphyxia, 13.75 (2.48, 76.31) times more likely to have hypoglycaemia and 2.32 (1.03, 5.26) times more likely to have respiratory distress (RD) than SGA infants with adequate PI (SGA-API). The increased risks of asphyxia and hypoglycaemia observed for SGA-LPI infants diminished, but remained statistically significant after controlling for the infant's gender, birthweight, gestational age and hospital of birth. There was no difference in risk of hyperbilirubinaemia between SGA-API and SGA-LPI infants. With the exception of risk of hyperbilirubinaemia, SGA-API infants carried the same risks of morbidity as non-SGA infants. The results of the study show that SGA infants do not constitute a homogeneous group with respect to their prospects for early postnatal health and survival. Furthermore, the pattern of differences in morbidity risk between SGA-API and SGA-LPI infants observed in this study is consistent with the timing hypothesis for the aetiology of variation in PI among SGA infants.

Oxygen diffusive conductances of human placentae from term pregnancies at low and high altitudes

A morphometric model of oxygen diffusion is employed to calculate the partial, total and specific conductances of human placentae from low- and high-altitude term pregnancies. Placentae were obtained from indigenous and non-indigenous populations and the diffusion pathway dissected into six tissue compartments. Birthweights were reduced at high altitude but were greater in natives versus non-natives. The altitudinal differences were associated with changes in placental diffusive conductances. The partial conductance of the villous trophoblast was conserved but the conductance on the maternal side was increased as was the conductance of the villous stroma. Fetal conductances were conserved (plasma) or diminished (erythrocytes). We conclude that birthweights are reduced at high altitude despite the attempts to increase the total placental diffusive conductance for oxygen. The mechanisms underlying these adaptations are discussed.

Consequences for maternal nutrition of reproductive stress across consecutive pregnancies

Frequent cycles of reproduction increase the risk that lactation will overlap with pregnancy and shorten the duration of the recuperative interval (nonpregnant and nonlactating portion) within the reproductive cycle, thereby increasing the risk of maternal nutritional depletion. Nutritional responses to these stresses have been demonstrated by contrasting groups of women with different experiences; however, these relationships may be spurious and the result of third factors. In this study, responses to changing stress over consecutive pregnancies were studied and contrasted within individual Guatemalan women; biases caused by factors constant to women were eliminated. Stress was assessed by examining responses in maternal supplement intake, maternal fat stores, and birth weight. Overlap and short recuperative intervals were found to be stressful (in that order) for mothers as shown by increased supplement intake and reduced fat stores. Birth weight in term gestations was not affected, indicating that fetal growth is being protected at the cost of maternal nutritional status.

Iron deficiency and behavior: criteria for testing causality

The association between iron deficiency and poor behavioral-test performance is well established. The question of causality, however, remains unanswered. This paper presents the essential criteria for a valid test of causality. Internal validity is examined in terms of positive and negative findings. Plausibility of the findings requires analyzing the congruency of the results; for example, those who respond to the iron treatment are also those who respond behaviorally. External validity describes the extent to which inferences may be made about other populations or circumstances.

Growth patterns of school-children in Bahrain

The aim of this study is to assess physical growth of school children in Bahrain. Cross-sectional data on 1593 children (818 boys and 775 girls), aged 6.5 to 18.5 years were collected in 1986. Anthropometric measures included height, weight, mid-arm circumference, triceps, biceps, subscapular and suprailiac skinfold thickness. At all ages median (P50) heights and weights of Bahraini boys and girls are below the 50th percentiles of the North American reference standard (NCHS). Median heights of both Bahraini sexes falls between the 25th and 5th percentiles of the reference data. As for weight, the median of boys fluctuates between the 25th and 5th percentiles, while that of girls fluctuates between the 50th and 10th percentiles of the standard. When compared to the American standard, median triceps skinfold of Bahraini boys and girls falls between the 50th and 25th percentiles. The median arm circumference of both sexes is close to the 5th percentiles. In general, the skinfold measurements indicate a high subcutaneous fat store, suggesting a lack of muscle development. Health, genetic and other factors associated with growth patterns of Bahraini children are discussed.

Body composition and energy intake: do overweight women overeat and underreport?

The relationship between energy consumption and body composition was evaluated in 63 women by use of energy-intake values that were precisely measured in a metabolic unit and corrected for deviations from energy balance. Energy requirement for the maintenance of body weight was not significantly correlated with adiposity expressed as percent body fat. However, energy requirement was positively associated with lean mass (p less than 0.0001) whereas fat mass added no predictive value to the same multivariate regression equation. Self-reported energy intake (before the experiments) was not correlated with lean mass and was underestimated by lean subjects at least as much as by obese subjects. Discrepant findings in the literature concerning relationships between obesity and energy intake may be explained by reporting error and by the relative lean mass of obese vs nonobese women but not by systematic underreporting unique to obese subjects.

Accuracy of heart-rate monitoring and activity diaries for estimating energy expenditure

The accuracy of heart-rate monitoring and activity diaries for measuring energy expenditure in free-living individuals was studied in 12 women. Estimates of energy expenditure were calculated from heart-rate monitoring by use of four different prediction equations to describe the relationship between heart rate and energy expenditure. Estimates of energy expenditure from activity diaries were calculated using both individually measured and published values for the energy cost of activities. Energy intake adjusted for changes in body-energy stores was used as a reference. Heart-rate monitoring overestimated group energy expenditure from 2 to 9% and the errors in estimating individual energy expenditure ranged from -53 to 67%. Activity diaries underestimated group energy expenditure by 2-6% and the errors in estimating individual energy expenditure ranged from -39 to 56%. Heart-rate monitoring and activity diaries may prove useful for estimating the energy expenditure of groups but not individuals.

Iron deficiency anemia and steady-state work performance at high altitude

Thirty-seven young adult male highland residents at 3,600-4,100 m in La Paz, Bolivia, performed short-duration cycle ergometry at 60, 80, and 100% of maximal voluntary O2 consumption (VO2max). Three groups of subjects representing the high-altitude population mean hemoglobin (Hb), the 10th percentile Hb, and below the 1st percentile were examined to test the hypothesis that the relationship of exercise performance to Hb concentration is similar to those relationships established at low altitude. Anemic individuals (n = 8) had 23% lower voluntary VO2max and 28% lower maximal work loads compared with controls (n = 17) or marginally anemic subjects (n = 12) although the relationship of VO2 to work load was similar. Anemic individuals maintained significantly higher arterial O2 partial pressures and Hb saturations during heavy exercise (90 +/- 0.5 vs. 85 +/- 0.6%) in conjunction with a greater heart rate up to maximal effort. A significantly decreased erythrocyte 2,3-diphosphoglycerate (2,3-DPG)-to-Hb molar ratio (0.70 +/- 0.04 vs. 1.12 +/- 0.06), suggestive of a left-shifted dissociation curve in anemics, is in contrast to the expected right-shifted curve. Moderate anemics were similar to controls. Anemic individuals did not differ in arterial lactate concentration from controls at absolute work loads; anemics had significantly lower arterial lactate concentrations at maximal effort than controls with no differences in the work load-to-lactate relationship. In conclusion, O2 transport during exercise at high altitude seems unaffected by the Hb concentrations as low as the 10th percentile of the population mean.(ABSTRACT TRUNCATED AT 250 WORDS)

On the factors which contribute to thinning of the villous membrane in human placentae at high altitude. II. An increase in the degree of peripheralization of fetal capillaries

The contribution made by fetal capillary peripheralization to the thinning of the villous membrane seen in human placentae from high-altitude pregnancies is examined by stereological methods. Variables characterizing the shape of the villous core and the spatial relationships between trophoblast and capillaries are quantified. They shed light on the relative importance of dynamic versus mechanistic processes of villous membrane attenuation. Highland villi differ from lowland villi in several ways. On average, they possess a thinner barrier due to closer approximation of capillaries to overlying trophoblast; in consequence, the villous core is more irregular in outline and its surface (that of the inner aspect of the trophoblast) exceeds in area that of the outer aspect of the trophoblast. These results suggest that the dynamic process (protoplasmic streaming within syncytiotrophoblast) cannot alone explain thinning of the villous membrane. A mechanistic process (capillary peripheralization and obtrusion into the trophoblastic epithelium) is sufficient to account for the differences observed, although the possibility that both processes operate concurrently cannot be discounted. This report completes a study into factors contributing to villous membrane thinning at high altitude.

On the factors which contribute to thinning of the villous membrane in human placentae at high altitude. I. Thinning and regional variation in thickness of trophoblast

Sections of human term placentae delivered at low and high altitude to indigenous and non-indigenous populations in Bolivia were analysed by stereological methods. Estimates were obtained of the arithmetic and harmonic mean thicknesses of villous membrane and of trophoblast. These values were then used to derive indices of thickness variation. No significant ethnic, sex or interaction effects were found. At high altitude, the villous membrane was significantly more variable in thickness owing to a lower harmonic mean but the same arithmetic mean thickness. Alterations in the arithmetic and harmonic mean thicknesses of the trophoblast contributed to the thinning of the villous membrane. The trophoblast was thinner and more irregular in thickness at high altitude. These findings are discussed in the context of placental diffusing capacity and the possible mechanisms for formation of vasculosyncytial membranes.

Morphometric studies on villi in human term placentae and the effects of altitude, ethnic grouping and sex of newborn

Stereological methods were used to test whether or not altitudinal, ethnic and sex differences in birthweight in Bolivia are associated with differences in placental morphology. Estimates of the volumes, surface areas, lengths and diameters of villi and of fetal capillaries were obtained by analysing paraffin sections of tissue. The average highland placenta contains villi of smaller overall volume, surface area and length. These villi possess a less voluminous fetal vascular space, and the capillaries are smaller in mean diameter. The average Amerindian placenta has longer but thinner capillaries than the average placenta delivered by non-indigenous women. Altitude and ethnic grouping interact to have an effect on total villous length, whilst ethnic grouping and sex interact to influence fetal capillary length. These structural differences are discussed in the context of their likely impact on placental functioning, notably on exchange by passive diffusion.

Variation in early neonatal mortality for different types of fetal growth retardation

Birth and first-48-hr death records were analyzed for 10,024 liveborn infants in Mexico City and 12,786 liveborn infants in Santa Cruz, Bolivia. The objective of the analysis was to characterize the early postnatal mortality rates for different types of fetal growth retardation and prematurity. Infants who were delivered prior to 37 weeks of gestation had 23-100 times the mortality risk of infants born at full term and normal weight. Light-for-gestational-age infants (birth weight less than 2,900 g) were further divided into proportionately growth-retarded with normal Rohrer's index (weight/height) and disproportionately growth-retarded with low Rohrer's index. The proportionately growth-retarded infant had nearly twice the mortality of the full-term, appropriate-weight infants, whereas the disproportionately growth-retarded infants had 2.9-5.7 times the mortality rate of the full-term, appropriate-weight infants. There were some differences between samples in mortality rates and prevalence of the different classes of small infants, but the pattern of mortality within samples was consistent between samples.

The volumetric composition of human term placentae: altitudinal, ethnic and sex differences in Bolivia

Point counting volumetry has been used to decide whether or not altitudinal, ethnic and sex differences in birth weight in Bolivia are accompanied by changes in placental composition. Sixty eight placentae from healthy, term pregnancies were sampled from populations of Amerindian and non-Indian women living in Santa Cruz (400 m) and La Paz (3600 m). Altitudinal reductions in birth weight were not accompanied by significant alterations in placental weight yet highland placentae were substantially different in histological composition. On average, the highland placenta had a more voluminous intervillous space but reduced volumes of villi, juxtavillous fibrin and non-parenchyma. Whilst Amerindian newborn were heavier, placental weights were similar in both ethnic groups. However, the Amerindian placenta tended to possess more trophoblast and more villous stroma than its non-Indian counterpart. No sex differences were detected save for an interaction effect on fibrin which involved altitude, ethnic group and sex. Findings are discussed in the context of known morphometric and physiological differences between placentae in different experimental groups, notably in other types of pregnancy associated with reduced fetal growth.

Functional anemia of complicated protein-energy malnutrition at high altitude

The effect of severe protein-energy malnutrition (PEM) on erythropoiesis in children living in the highlands of Bolivia, altitude 3700 m, was studied. Forty percent reduced hemoglobin concentrations, significantly lower arterial oxygen tensions, and a right-shifted, oxygen-dissociation curve were observed compared to high-altitude controls. Serum and erythrocyte folate concentrations were 44% and 82%, respectively, of control values. Low initial transferrin saturation decreased significantly during the 10-wk refeeding period. Thus, iron and folate deficiency contributed significantly to the poor red cell response. Results suggest that the anemia associated with severe PEM has a more significant impact on oxygen transport at high altitude than at sea level and requires an adaptive response in the oxygen-dissociation curve to satisfy tissue-oxygen demands. Furthermore, marginal iron and folate status and an inflammatory block of iron supply may limit the reestablishment of a normal tissue mass during refeeding.

Hematologic evidence of fetal hypoxia among newborn infants at high altitude in Bolivia

The reduced birth weight widely reported for high-altitude infants has been attributed to intrauterine hypoxia. This assertion may be tested by comparing hematologic values of high-altitude and low-altitude newborn infants, since the human fetus can respond to intrauterine hypoxia with enhanced erythropoiesis. This report presents cord blood values of term Bolivian infants classified by altitude, ethnic group, and parity: 105 from La Paz (3600 m) and 46 from Santa Cruz (400 m). Hematocrit, hemoglobin concentration, and the proportion of hemoglobin F are higher among newborn infants at high altitude. Ethnic group and parity interact with altitude in effect on hematocrit and hemoglobin concentration. Gestational age, birth weight, maternal hematologic variables, and socioeconomic indicators are not significantly associated with cord blood values. The high-altitude newborn infant displays evidence of enhanced erythropoiesis, which supports the suggestion that the high-altitude fetus experiences a greater degree of hypoxia in utero than does the low-altitude fetus.

Combined effects of exercise and restriction of energy intake on moderately obese women

The current study was designed to assess the contribution of dietary-induced weight reduction on improvements in functional capacity in moderate obesity. Twelve females (means age = 29 yr, means fat percentage = 37%) served as subjects for the study. Subjects trained on a cycle ergometer 30 min.day-1, six day.wk-1 for three or six weeks at 75 to 85 per cent of maximum heart rate (HR max). Improvements in maximal oxygen uptake (delta VO2 max I.min-1) and functional capacity (delta VO2 max ml.kg-1 min-1) were compared in an attempt to separate out training and dietary effects respectively. Measurements were also taken on both the cycle ergometer and treadmill to test for any specificity of training effects. Changes in body composition were assessed by densitometry. Following three weeks of training, there was an average increase in VO2 max ml.kg-1 min-1 on the cycle ergometer and the treadmill of 14 and 19 per cent respectively. By six weeks, this had increased to 18 and 26 per cent respectively. The contribution of weight reduction to the improvements in functional capacity was calculated to range from 20 to 33 per cent. Thus, both energy restriction and exercise training appear to be effective means of improving functional capacity in moderately obese women.

The effects of exposure misclassification on estimates of relative risk

In epidemiologic studies, individuals may be misclassified with respect to exposure to a risk factor for disease. Such misclassification causes the relative risk of disease associated with the exposure in the population to be biased toward the null value. Here, a formula is derived for the apparent relative risk under misclassification (R) as a function of the sensitivity (U) and specificity (V) of the test for exposure and of the true relative risk (R) and true prevalence of exposure (P(E] in the population. The relative influence of U and V on the bias in R depends both on R and on P(E), with U tending to be more influential at higher values of P(E). When there is misclassification of exposure, variation in P(E) may bias comparisons of relative risk between groups or exposures, either by producing spurious differences or by masking true differences, and may generate spurious trends associated with a third variable such as age. Because the possible effects of misclassification of exposure on relative risk are complex and not easily generalized, the potential degree of bias should be evaluated individually in each situation.

Microscopical morphology of the human placenta and its effects on oxygen diffusion: a morphometric model

A combination of stereological and physicochemical data was used to estimate the oxygen-diffusing capacity of the human term placenta. The effects on this morphometric diffusing capacity of isolated changes in placental structure were investigated by permitting volumes, surface areas and harmonic mean diffusion distances to deviate from normal baseline (term) values. Diffusion performance could be monitored effectively by estimating only three structural quantities. The most influential variable was the harmonic mean thickness of the villous membrane followed by the surface areas of villi and of fetal capillaries. Blood space volumes and plasma diffusion distances had negligible effects on diffusing capacity. Conclusions are discussed in the context of published findings on changes in placental anatomy which occur during gestation, abnormal pregnancies and pregnancies at high altitude.

Distribution of hemoglobin and functional consequences of anemia in adult males at high altitude

In order to assess better the normal hemoglobin (Hb) range among adult males at high altitude, a hematological survey was completed in La Paz, Bolivia (3700 m). Two statistical methodologies were utilized to identify the anemic and polycythemic contributions to the Hb distribution of normal healthy men (n = 526). The Hb of normal men has a Gaussian distribution with mean and SD of 18.8 +/- 1.4 g/dl. Cutoff levels of 15.8 and 22.0 g/dl Hb were selected to identify the anemic and polycythemic subpopulations. Iron status in this high altitude population is similar to that of low altitude populations, and iron deficiency is the cause of most anemia found. An exercise test on a subsample of 56 men was utilized to validate the anemia cutoff level. Anemics as identified by the 15.8 g/dl Hb level showed a significant reduction in aerobic capacity as measured by PWC150 and estimated VO2max.

Stereological studies on the true thickness of the villous membrane in human term placentae: a study of placentae from high-altitude pregnancies

Stereological principles were used to calculate functionally significant dimensions of the human villous membrane, its arithmetic mean thickness (Ta) and its harmonic mean thickness (Th). The former is proportional to tissue mass and oxygen consumption, the latter to diffusional resistance. For a group of 15 term placentae from uncomplicated pregnancies at high altitude, the average values were Ta = 4.44 micron, Th = 3.56 micron and Ta/Th = 1.26. The latter figure provides a useful quantitative expression for the efficiency of the membrane in gas and metabolite diffusion. It implies that vasculosyncytial membranes and syncytial knots decrease resistance to diffusion by 26 per cent, compared with that of a membrane with uniform thickness throughout. The methods are simple to apply and provide better estimates of true thickness than do measurements confined to thin sections.

Structure-function correlation in the human placenta: the morphometric diffusing capacity for oxygen at full term

A combination of stereology and physiology is used to estimate the morphometric diffusing capacity for oxygen of the normal human placenta at term. The morphometric diffusing capacity is found to be higher than published values determined by physiological methods. The most likely explanation for this discrepancy is that physiological values are too low because of the effects of shunts, placental oxygen consumption and uneven diffusion:perfusion ratios. Despite the discrepancy, morphometry of histological sections offers a valuable and practicable alternative for comparing the functional potential of the placenta in different species, during normal gestation, disease, experimental treatment and environmental hypoxic stress.

Work performance of high-altitude Aymara males

The sample for this study consisted of 28 Aymara males between the ages of 15 and 43 years. The subjects were rural high-altitude natives who were temporarily working as porters in La Paz, Bolivia (3700 m). Mean VO2max was 46 X 5 ml/kg/min. There was a significant negative relationship between VO2max and age in adult porters . However, there was also a significant positive relationship between maximal work output and age and a significant negative relationship between VO2 during submaximal exercise and age. Relative work intensity (VO2/VO2max) during submaximal exercise did not change significantly with age. Thus, even though VO2max decreased significantly with age, these data suggest that there may not be a substantial decrease with age in the adaptive status of these men. Minimal support was found for the hypothesis that chest size in Andean highlanders influences the effectiveness of the oxygen transport system.

Anthropometric survey of high-altitude Bolivian porters

This paper presents the results of an anthropometric survey of 138 rural Aymaran high-altitude males who were working as porters in La Paz, Bolivia (3700 m). All subjects were measured for stature, weight, upper arm circumference, and triceps skinfolds. The body size and composition of the porters were then compared to an Aymaran rural population from the Bolivian highlands, and urban mestizo labourers from La Paz. The porters were smaller than the urban sample, but appeared to be generally representative of rural Aymaran natives with respect to body size and composition, and nutritional status. It is suggested that towards one extreme of nutritional variability, some degree of undernutrition may be indicated, which should be considered in future studies of adaptation to hypoxia among these Andean highlanders.

Effects of exercise on riboflavin requirements of young women

The riboflavin requirement of young women during periods of sedentary living and exercise was determined during a 12-wk metabolic study. The study was divided into a 6-wk no exercise period followed by a 6-wk exercise period in which subjects jogged around a track for 20 to 50 min/day. Twelve subjects, aged 19 to 27 yr, were fed a basic diet containing 0.6 mg riboflavin/1000 kcal of intake. Riboflavin intake was increased by 0.2 mg/1000 kcal increments by provision of riboflavin in a glucose polymer mixture. Linear regression analysis was used to estimate the riboflavin intake required for an erythrocyte glutathione reductase activity coefficient of 1.25 during both the no exercise and exercise periods. Individual riboflavin requirements ranged from 0.62 to 1.21 mg/1000 kcal before exercise and 0.63 to 1.4 mg/1000 kcal during the exercise periods. Riboflavin requirement could not be related to the kilocalorie intake or lean body mass of the subjects. It is concluded that healthy young women require more riboflavin to achieve biochemical normality than the 1980 Recommended Dietary Allowances and that exercise increases riboflavin requirements.