This is a frequent claim that is made about milks effects on human biology: it makes children grow. What is the evidence for this claim? What components of milk might be involved? What is the significance of growth in height? What is milks relationship to strong bones?

© 2011 Taylor and Francis Advertisement from the National Dairy Products Association. Text reads: Thereve been some changes, all right, in the past generation … For one thing – Betsy Co-eds grown a good bit taller since mother played center on the team! … This doesnt mean were raising a race of Amazons …. But it does mean younger folk have better foods to grow on than their parents ever did …. Many of them are developments of National Dairy Laboratories … that milk, natures most nearly perfect food, offers virtually all the raw materials of modern nutritional research. (Source: Journal of the American Dietetics Association (1947)).

Supplementation studies – very few control for energy intake. © 2011 Taylor and Francis Study published in The Lancet in 1929 demonstrating that children receiving a milk supplement grew more in height over a period of seven months than those who received nothing or a biscuit of caloric value equal to the skimmed milk supplement (Source: Drawn from data published in Leighton and Clark (1929)).

© 2011 Taylor and Francis Well-controlled study from Kenya found no special effect of milk supplementation on growth in height of schoolchildren, even those with marginal nutritional status at baseline. Low HAZ are relatively well-nourished (z-score>1.4). High HAZ children are those with z-scores 1.4 below the median height at baseline (Source: Grillenberger et al.(2003: 91)).

© 2011 Taylor and Francis

Difference in height growth curves between white, non-Hispanic girls who drank >3 servings of milk per day and those who drank (Source: Reproduced and adapted with permission from the American Association for Cancer Research: Berkey et al). Note that at baseline (age 10 yrs), there was little difference in height among those who drank a lot vs. little milk; these differences became exaggerated during the adolescent growth period.

Calcium – no evidence that calcium supplementation increases height Insulin-like growth factor I (IGF-I) – people who drink more milk have higher IGF-I levels; IGF-I levels are higher in individuals who are taller Milk contains IGF-I and you also produce your own – it is not known if the greater IGF-I in individuals who drink more milk is due to the IGF-I in cows milk or if milk stimulates IGF-I production in the body. IGF-I is an important growth factor in bone tissue. © 2011 Taylor and Francis

Milk and calcium are often equated with each other Milk is rich in many micronutrients and calcium is found in plant foods. Cows milk contains much more calcium than human milk. U.S. children dont meet recommended daily intake values. Question is whether U.S. recommendations are too high? Theyre higher than other countries. Assume that boosting calcium intake will happen only by boosting milk or dairy intake. © 2011 Taylor and Francis

Bone density and bone size are different aspects of bone biology Some studies show a positive effect of milk supplementation on bone density; others do not. Bone density is affected by numerous factors including weight-bearing exercise, Vitamin D status, and genetic inheritance. © 2011 Taylor and Francis

Bone fracture and osteoporosis rates are highest in countries with highest levels of dairy intake. Why? Also have lowest exposure to UVB – hence lower Vitamin D production; less engagement with subsistence activities (i.e. less weight-bearing exercise), higher animal protein intake, and many other factors that contribute to variation in bone density are likely involved. © 2011 Taylor and Francis

Recent promotions have highlighted dairys contribution to weight loss or healthy weight. Is this at odds with drink milk and grow messages? Ideal American is tall and slender - can milk help attain both of these dimensions of ideal size? © 2011 Taylor and Francis