Andrea S. Wiley

Dairy and milk consumption and child growth: Is BMI involved? An analysis of NHANES 1999–2004

Humans are unique among mammals in that many consume cows milk or other dairy products well beyond the traditional age of weaning. Milk provides various nutrients and bioactive molecules to support growth and development, and the question arises as to whether this dietary behavior influences growth parameters. There is evidence that milk makes positive contributions to growth in height, but its associations with other aspects of body size, such as body mass index (BMI), are not well‐established. National Health and Nutrition Examination Survey (NHANES) data from 1999 to 2004 and multivariate regression analysis were used to test the hypothesis that milk (g) or total dairy product consumption (kJ) is associated with higher BMI percentile among US White, Black, and Mexican‐American children of age 2–4 years (n = 1,493) and 5–10 years (n = 2,526). Younger children in the highest quartile of dairy intake had higher BMIs (β = 7.5–8.0; P < 0.01) than those in the lowest two quartiles. Controlling for energy intake eliminated differences between QIV and QI. Among children of 5–10 years of age dairy intake had no relationship to BMI. Young children in the highest quartile of milk intake had higher BMIs than all lower quartiles (β = 7.1–12.8; β = 6.3–11.8 in energy‐controlled models; P < 0.05). Among children of 5–10 years of age, those in QIV for milk intake had higher BMIs than those in QII (β = 8.3; β = 7.1 in energy‐controlled model; P < 0.01). Controlling for total protein or calcium did not change the results. Milk had more consistent positive associations with BMI than did dairy products, and these were strongest among children of 2–4 years of age. Am. J. Hum. Biol., 2010.

Milk Intake and Total Dairy Consumption: Associations with Early Menarche in NHANES 1999-2004

Background Several components of dairy products have been linked to earlier menarche. Methods/Findings This study assessed whether positive associations exist between childhood milk consumption and age at menarche or the likelihood of early menarche (<12 yrs) in a U.S sample. Data derive from the National Health and Nutrition Examination Survey (NHANES) 1999–2004. Two samples were utilized: 2657 women age 20–49 yrs and 1008 girls age 9–12 yrs. In regression analysis, a weak negative relationship was found between frequency of milk consumption at 5–12 yrs and age at menarche (daily milk intake β = −0.32, P<0.10; “sometimes/variable milk intake” β = −0.38, P<0.06, each compared to intake rarely/never). Cox regression yielded no greater risk of early menarche among those who drank milk “sometimes/varied” or daily vs. never/rarely (HR: 1.20, P<0.42, HR: 1.25, P<0.23, respectively). Among the 9–12 yr olds, Cox regression indicated that neither total dairy kcal, calcium and protein, nor daily milk intake in the past 30 days contributed to early menarche. Girls in the middle tertile of milk intake had a marginally lower risk of early menarche than those in the highest tertile (HR: 0.6, P<0.06). Those in the lowest tertiles of dairy fat intake had a greater risk of early menarche than those in the highest (HR: 1.5, P<0.05, HR: 1.6, P<0.07, lowest and middle tertile, respectively), while those with the lowest calcium intake had a lower risk of early menarche (HR: 0.6, P<0.05) than those in the highest tertile. These relationships remained after adjusting for overweight or overweight and height percentile; both increased the risk of earlier menarche. Blacks were more likely than Whites to reach menarche early (HR: 1.7, P<0.03), but not after controlling for overweight. Conclusions There is some evidence that greater milk intake is associated with an increased risk of early menarche, or a lower age at menarche.

Consumption of milk, but not other dairy products, is associated with height among US preschool children in NHANES 1999–2002

Background: Little is known about how cows milk consumption affects growth of young children. Aim: The present study evaluated associations between milk consumption and height among preschool-age children in three ethnic groups in the USA. Subjects and methods: A sample of 1002 children aged 24–59 months from NHANES 1999–2002 was used. Multivariate regression tested for associations between milk consumption (milk kJ/total kJ from 24 h recall, daily vs less frequent intake over 30 days) and height, controlling for age, sex, ethnicity, birth weight, and energy intake. Results: Children in the highest quartile of milk intake (QIV) were taller (1.1–1.2 cm; p<0.01) than those in QII and QIII but not QI. Total calcium had a positive effect on height (p<0.01), but did not change the height differences among percentiles. Total protein was not associated with height and QIV children were taller (0.9–1.2 cm) than those in all other quartiles. Children who drank milk daily were taller (1.0 cm; p<0.02) than those with less frequent intake. Consumption of other dairy products (other dairy kJ/total kJ) had no association with height. Blacks were taller than Whites and Mexican-Americans; controlling for milk intake did not alter this pattern. Conclusion: Milk contributes positively to height among preschool children; this association was not found for non-milk dairy products.

THE ECOLOGY OF LOW NATURAL FERTILITY IN LADAKH

The existence of very low rates of fertility among non-contracepting human populations has intrigued researchers in demography and reproductive ecology. Long inter-birth intervals, driven primarily by the lactational amenorrhoea associated with breast-feeding, have been shown to be important determinants of low natural fertility in several populations. Other reports have suggested that sterility brought about by sexually transmitted diseases (STDs) might also explain low fertility in some populations, especially in Africa. This report presents an analysis of 1981 Indian census data that documents low natural fertility in Ladakh, a high-altitude region of the Himalaya in north India. In Ladakh, there is evidence for low rates of marriage among women that may be attributable to the practice of polyandry, but also high rates of primary and secondary sterility within marriage, resulting in low completed parities for post-reproductive age married women. Age-specific fertility rates derived from the number of current births are also unexpectedly low. Hypotheses to explain very low fertility in Ladakh are considered from among the likely proximate determinants and evaluated using two supplementary sources of information derived from fieldwork in Ladakh in the early 1990s. The most likely explanations for low marital fertility include sterility from STDs, high rates of fetal loss, and possibly nutritional contraints on ovarian hormone status.

Neonatal and maternal anthropometric characteristics in a high altitude population of the western Himalaya

A study of neonatal anthropometric characteristics was undertaken in Ladakh, India, a region comprising the western portion of the trans‐Himalayan plateau. The object was to better understand the dynamics of high altitude adaptation in the Himalaya. In a largely native sample of 168 women and their newborns, mean birth weight was 2,764 g, mean length was 48.02 cm, and mean Ponderal Index (PI) was 2.49. Female newborns were significantly lighter and shorter than males. Overall, 27% of newborns fell into the standard category of infants at increased risk of mortality ( < 2,500 g); 37% of females and 17% of males were so classified. In multivariate regression analysis, maternal weight and the sex and gestational age of the newborn were the only significant predictors of birth weight, but explained a small (18%) part of the variance. Compared to Andean and Tibetan samples, Ladakhi newborns were between 300 and 550 g lighter. This variation is explained, in part, by maternal characteristics, such as lower average parity, age, and weight. Reproductive capacity appears to be compromised in this population because of inadequate nutrition in the face of high energy demands of agricultural work, which may further compromise maternal adaptation to hypoxic conditions. The population of Ladakh has a relatively recent ancestry in this high altitude region and is likely a genetically heterogeneous population from an extensive history of immigration. Thus it is possible that the low average birth weight in Ladakh may also be influenced by inadequate genetic adaptation to hypoxia.

Milk for “Growth”: Global and Local Meanings of Milk Consumption in China, India, and the United States

Whereas milk production and consumption and the genes that allow for milk digestion throughout life are strongly variable across populations, historically only a minority of human groups valued milk as an important component of local foodways. By the early 21st century, however, milk consumption has become globally normative, and a spectacular rise in intake has been documented in countries such as China and India. Meanwhile, in the United States, consumption has declined markedly, especially among children. In this article, I argue that milk has been able to succeed in India and China by being positioned as a food with special qualities that enhance physical growth, which in turn serves as a powerful metaphor for individual and national power and wealth. Simultaneously, milk is being repackaged as a salve for the problems of modernity in the United States. Milks unique history in each country provides an interpretive framework within which these meanings emerge, and milks current success in local foodways depends on traditional modes of processing.

The Globalization of Cow's Milk Production and Consumption: Biocultural Perspectives

Cows milk consumption has been relatively rare in human history, largely confined to populations with genetic adaptations for continued production of lactase, the enzyme that breaks down the unique milk sugar lactose. But in the last forty years, both the production and consumption of cows milk have spread around the world, and trade in milk products has likewise increased. Populations with no history of milk drinking have embraced this new beverage, and governments promote its consumption in their food-based dietary guidelines and school milk programs. China is a particularly good example of this trend. There the dairy industry is growing rapidly and milk consumption has become increasingly common in urban areas. Milk is viewed as especially appropriate for children, with growth-promoting properties; the larger size and athletic success of western athletes is often attributed to their greater milk consumption. Milk is a very unusual food insofar as it is uniquely produced by mammals to support the growth, maturation, and health of nursing infants. Furthermore, there is variation among human populations with respect to the production of lactase in adulthood (lactase persistence/impersistence); consumption of lactose, which is only found in milk, beyond the traditional nursing period can result in the gastrointestinal symptoms of lactose intolerance. Thus the surge in consumption among lactase impersistent populations is likely to be accompanied by increases in digestive complaints. With regard to the purported positive relationship between milk and growth, the current evidence is not compelling that milk consumption in childhood results in significant gains in height.

Rethinking the starch digestion hypothesis for AMY1 copy number variation in humans

Alpha-amylase exists across taxonomic kingdoms with a deep evolutionary history of gene duplications that resulted in several α-amylase paralogs. Copy number variation (CNV) in the salivary α-amylase gene (AMY1) exists in many taxa, but among primates, humans appear to have higher average AMY1 copies than nonhuman primates. Additionally, AMY1 CNV in humans has been associated with starch content of diets, and one known function of α-amylase is its involvement in starch digestion. Thus high AMY1 CNV is considered to result from selection favoring more efficient starch digestion in the Homo lineage. Here, we present several lines of evidence that challenge the hypothesis that increased AMY1 CNV is an adaptation to starch consumption. We observe that α- amylase plays a very limited role in starch digestion, with additional steps required for starch digestion and glucose metabolism. Specifically, we note that α-amylase hydrolysis only produces a minute amount of free glucose with further enzymatic digestion and glucose absorption being rate-limiting steps for glucose availability. Indeed α-amylase is nonessential for starch digestion since sucrase-isomaltase and maltase-glucoamylase can hydrolyze whole starch granules while releasing glucose. While higher AMY1 CN and CNV among human populations may result from natural selection, existing evidence does not support starch digestion as the major selective force. We report that in humans α-amylase is expressed in several other tissues where it may have potential roles of evolutionary significance.

A Role for Biology in the Cultural Ecology of Ladakh

Human ecology research in the high-altitude region of Ladakh (northern India) has tended to focus on the adaptive significance of Ladakhi social institutions given a natural environment characterized by numerous challenges. This research appears to lead to the conclusion that traditionally-living Ladakhis are in a state of well-being and harmonious balance with their environment, as social institutions such as polyandry constrain fertility to keep the population size in check relative to constrained resources. There has been little research on biological adaptation in Ladakh, and the view from biology presents a very different picture of the relationship between Ladakhis and their environment. Data presented here show that the health of reproductive women and infants is compromised by both natural and social factors. Since reproductive health is crucial to the production of future generations, it is argued that mortality plays a major role in constraining population growth in Ladakh, and may be due to the limited biological history that Ladakhis have in this high-altitude region. This may also help us understand Ladakhi patterns in relation to those observed in the Andes.

Longitudinal change of selected human milk oligosaccharides and association to infants’ growth, an observatory, single center, longitudinal cohort study

Background Human milk is the recommended and sole nutrient source for newborns. One of the largest components of human milk is oligosaccharides (HMOs) with major constituents determined by the mother genotype for the fucosyltransferase 2 (FUT2, secretor) gene. HMO variation has been related with infant microbiota establishment, diarrhea incidence, morbidity and mortality, IgE associated eczema and body composition. Objectives We investigated the (i) dependence of several major representative HMOs on the FUT2 status assessed through breast milk 2’Fucosyllactose (2’FL) and (ii) the relation of the 2’FL status with infant growth up to 4 months of life. Design From an open observatory, single center, longitudinal cohort study with quantitative human milk collection at 30, 60, and 120 days postpartum from 50 mothers, who gave birth to 25 female and 25 male singleton infants, we collected a representative sample of human milk. We quantified the following 5 representative HMOs: 2’FL, Lacto-N-tetraose (LNT), Lacto-N-neotetraose (LNnT), 3’Sialyllactose (3’SL) and 6’Sialyllactose (6’SL). We grouped the milk samples and corresponding infants according to the measured milk 2’FL concentrations at 30 days of lactation, which clustered around low concentrations (95% CI of mean 12–42 mg/L) and high concentrations (95% CI of mean 1880–2460 mg/L) with the former likely representing Secretor negative mothers. Infant anthropometric measures were recorded at birth, 1, 2 and 4 months of age. Relations among the quantified HMOs and the relation of the high and low 2’FL HMOs groups with infant growth parameters were investigated via linear mixed models. Results The milk samples with low 2’FL concentration had higher LNT and lower LNnT concentrations compared to the samples with high 2’FL. The milk 3’- and 6’SL concentrations were independent of 2’FL. Over lactation time we observed a drop in the concentration of 2’FL, LNT, LNnT and 6’SL, especially from 1 to 2 months, while 3’SL remained at relatively constant concentration from 1 month onwards. Up to 4 months of age, we did not observe significant differences in body weight, body length, body mass index and head circumference of the infants who consumed breast milk with low or high FUT2 associated HMO concentrations and composition. Conclusions Our findings on HMO concentrations over time of lactation and clusters based on 2’FL concentrations confirm previous observations and suggest that LNnT and LNT are ‘co-regulated’ with the FUT2 dependent 2’FL concentration, with LNnT showing a positive and LNT a negative relation. Further, our findings also suggest that the relatively substantial variation in HMOs between the high and low 2’FL clusters do not impact infant growth of either sex up to 4 months of age. The study was registered in www.ClinicalTrial.gov (NCT01805011).