Got milk? the good and the bad

Milk is socially accepted to be a healthy drink, with plenty of calcium, protein and vitamin D fortification.

And with government and celebrity sponsoring, along with it’s history in the American diet accompanying foods such as cereal and cookies, it makes a pretty appealing choice to most of the American public.

However New York Times writer Aaron E. Carroll would disagree.

He writes in his article, “Got Milk? Might Not Be Doing You Much Good” that milk, rather than being a beneficial part of the diet, may be unhelpful or even detrimental to health, despite the pushing from organizations such as USDA and others that suggest three cups for daily consumption.

Carroll reads in an article titled “Milk intake and risk of mortality and fractures in women and men: cohort studies”, that consumption of milk for Swedish men and women, all 39 or older, shows no associated protection from fracture for men and increased fracture risk in women, along with an association with increased risk of death for both sexes.

He also draws information from other studies, explaining how a 2007 meta analysis titled “Calcium intake and hip fracture risk in men and women: a meta- analysis of prospective cohort studies and randomized controlled trials” found no association between calcium intake and hip fracture risk, indicating that the calcium in milk may be irrelevant to hip bone integrity. While he does note that people with actual vitamin D or calcium deficiencies should be treated by supplementation, he also adds that most people in the US are not deficient, and that these people are likely the ones who receive the pitch that milk is beneficial. Also, while he acknowledges that breast milk is highly beneficial to children up to the age of two, he also makes a point to mention how humans are the only mammals on earth who continue to consume milk after childhood, making it clear that milk is not a necessity in child or adult diets. This, along with the fact that milk is a high calorie beverage loaded with proteins that most Americans do not actually need in their diets, leads him to believe that milk, much like a cookie, should only be enjoyed in moderation and because of taste preference rather than any health reasons.

While the information that Carroll pulls from the article “Milk intake and risk of mortality and fractures in women and men: cohort studies” is consistent with the data provided by the article itself, he fails to note several other points made within the very same article. For example, the authors mention that there is a correlation between increased milk consumption and unchanged or increased hip fractures for men and women, but also add that a reverse causation situation, in which milk consumption is increased due to the increased risk of osteoporosis rather than increased milk consumption leading to an increase in osteoporosis risk, is possible though it may be unlikely.

Similarly, the 2007 meta analysis he cites does mention calcium’s lack of significant impact on hip fracture risk, but it also notes that pure calcium supplementation may lead to increased risk of hip fractures due to the lack of other supporting micronutrients such as vitamin D and phosphorus from phosphate, rather than being a function of the calcium itself. While these alternate explanations and potentially mitigating factors are mentioned in the articles he cites, Carroll does not mention these himself, nor does he comment on the data related to fermented milk products, such as yogurts and cheeses, which actually do show an association with decreased rates of bone fracture and mortality.

Other articles, such as the “Milk Consumption During Teenage Years and Risk of Hip Fractures in Older Adults” article from the JAMA Pediatrics journal, support the claim made in Carroll’s article. This separate study found that after controlling for known risk factors and current milk consumption, every additional glass of milk per day consumed during teenage years was associated with a 9% higher risk of hip fracture in men. However, the association was weakened when correlated with the increase in height, as hip fracture risks were noted to increase by 4.5 to 5% for every centimeter of height. Because of this, there was ultimately no association between teenage milk consumption and hip fractures in women.

This article also mentions that fermented milk products such as cheese are not correlated with the risk of bone fracture in men and women, like the other scientific articles do and like Carroll fails to mention in his now news article. The paper notes as well in its comments that milk consumption during childhood and adolescence contributes to peak bone mass which is expected to help counter osteoporosis and bone fractures in later life, unlike Carroll’s assertion that milk is only beneficial to the health of infants to two year olds, and not beneficial at all beyond that. The authors of the article also notes that the results of the experiment may be limited to Caucasian adults, who were the main test subjects.

Ultimately, more research needs to be done into milk consumption to reach any solid conclusion, either for or against it.

Carroll’s warnings against drinking regular milk for health benefits do hold scientific weight, but nevertheless more refined research would help to better understand the exact effects of dairy in the system. Since fermented milk products have been found to be beneficial for the reduction of risk of hip fractures, for example, it would be beneficial to research the difference between various milk products in order to better determine exactly what the difference is. For example, it is hypothesized that the lactose in milk may be a major contributor to the negative correlation between bone health and milk consumption for adults due to the highly oxidative properties in the body, yet that would not be an issue for fermented products such as cheeses and yogurts where the lactose sugar has already been metabolized by microbes. In addition, depending on the effect of a cow’s feed on the milk composition, there could be a vast difference in the health benefits of milk from cows fed with corn verses grass, or in the environment in which the cow lives. Overall, Carroll’s article is prudent, as there is scientific evidence that milk is correlated with either no change or higher risk of bone fracture in adults, but does not take other dairy products into account.

Because of this, while milk itself may not be as beneficial as the USDA claims, it should not be discounted as a viable and healthy food source until more research is done.

References

1. Bischoff-Ferrari, H., Dawson-Hughes, B., Baron, J., Kanis, J., Orav, E., Staehelin, H., . . .
Willett, W. (2011). Milk intake and risk of hip fracture in men and women: A meta-analysis
of prospective cohort studies. Journal of Bone and Mineral Research J Bone Miner Res,
86(6), 833-839.

2. Carroll, A. (2014, November 17). Got Milk? Might Not Be Doing You Much Good. New
York Times. Retrieved May 19, 2015, from http://www.nytimes.com/2014/11/18/upshot/got
milk-might-not-be-doing-you-much-good.html

3. Feskanich, D., Bischoff-Ferrari, H., Frazier, A., & Willett, W. (2014). Milk Consumption
During Teenage Years and Risk of Hip Fractures in Older Adults. JAMA Pediatrics JAMA
Pediatr, 168(1), 54-54. doi:10.1001

4. Michaelsson, K., Wolk, A., Langenskiold, S., Basu, S., Lemming, E., Melhus, H., & Byberg,
L. (2014). Milk intake and risk of mortality and fractures in women and men: Cohort studies.
Bmj. doi:10.1136

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