Speed-Dependent Visual-Motor Tracking Differences in Children With Autism Relate to Core Symptoms.

Milk is widely consumed, particularly in Western countries. The Dietary Guidelines for Americans recommend three cup equivalents of dairy per day. In contrast, the Nutrition Source, an educational nutrition website from the Harvard School of Public Health, recommends limiting consumption to one to two servings per day, citing potential risks associated with milk consumption. The recommendation by the Nutrition Source is based on previous studies, but these studies were primarily conducted in the USA and predominantly involved White participants, with only limited representation of Asian populations across low- to high-income settings. Milk consumption varies substantially by country, culture and ethnicity, with Asians typically consuming less. In many cases, evidence of milk consumption comes from cohort studies that compare groups with higher milk consumption to those with lower milk consumption. Hence, the OR, risk ratio or hazard ratio derived from these studies is substantially influenced by the odds, risk and hazard of the lower consumption group. For Asian populations, it is conceivable that the impact of milk consumption differs from that in other populations, not only due to racial and genetic factors but also because of differences in average consumption patterns. This article compares past research on milk consumption and health outcomes, primarily from Western populations, with evidence from Asian populations to discuss effect heterogeneity of milk consumption. Because ‘dairy’ encompasses diverse products with varying health effects (e.g. butter, yogurt), analysing them together can be misleading. Therefore, this commentary specifically isolates milk to provide a clearer understanding of its health implications. The Nutrition Source cites past research on milk consumption and CVD. One US study analysed combined data from the Nurses’ Health Study, Nurses’ Health Study II and Health Professionals Follow-up Study, reporting higher CVD mortality with whole milk intake. In this study, the lowest consumption groups (Q1) had mean intakes of 0·52, 0·67 and 0·96 servings per day across the three samples (one serving = 240 ml), while the highest consumption groups (Q5) had mean intakes of 4·00, 4·09 and 6·43 servings per day, respectively. On the other hand, a Japanese study reported an association between milk consumption and a lower hazard of CVD-related mortality in males, whereas evidence was not strong in females. In this study, the lowest consumption group had a mean intake of only 0·5 grams per day in males and 2·6 grams per day in females, while the highest consumption group had mean intakes of 272·8 grams per day in males and 305·4 grams per day in females. Thus, both the lowest and highest milk consumption levels differed markedly across these studies. A meta-analysis that included both Asian and White populations found that consuming 200 ml of milk per day was most protective against stroke. A recent study using the China Kadoorie Biobank found that regular dairy consumption (four or more times per week) was associated with a higher hazard of CHD but a lower hazard of stroke compared with never or rare consumption. The heterogeneous findings on milk consumption appear to be explained not only by racial or ethnic differences but also by the actual levels of intake in low- and high-consumption groups. Thus, certain populations with lower milk consumption may benefit from increased milk intake. Other factors, such as residual confounding, may have also influenced the results. Moreover, the heterogeneous findings may reflect differences in the populations studied. For instance, the Nurses’ Health Study, Nurses’ Health Study II and Health Professionals Follow-up Study cohorts all consisted of medical professionals. Furthermore, there may be inconsistencies between the development of CHD and stroke, which could have affected the findings. The Nutrition Source cites a study showing that both skimmed milk and whole milk were associated with a higher risk of type 2 diabetes mellitus (T2DM). However, these findings were again based on the Nurses’ Health Study, Nurses’ Health Study II and Health Professionals Follow-up Study, which involved populations with higher baseline milk consumption. A meta-analysis of observational studies found that total milk consumption was associated with a higher risk of T2DM in European populations but a lower risk in the Asian population. This meta-analysis included a Japanese study, in which women who consumed more than 200 ml of milk per day had an OR of 0·87 for T2DM compared with women consuming less than 50 ml, although the association did not reach statistical significance. Another study enrolling Chinese individuals found that daily milk drinkers had a lower hazard of T2DM compared to non-drinkers. The median milk consumption in this study was only 20·5 grams per day, and 67 % of participants never or rarely drank milk. As with CVD, baseline consumption appears to inf