Health aspects of dairy

Health Aspects of Dairy Dairy in Our Culture by Lily Ahrens St. Olaf College, Northfield, MN
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Although dairy products are now many people’s favorite foods, one of the main attractions is the health benefits. A study involving the diets of women aged 19-50 years found dairy products contributed many nutrients, including 64% of their total calcium intake, 42% of their phosphorus intake, 32% of their potassium, 29% protein, 41% Vitamin B-12, 15% vitamin B6, 25% fat and 22% of their total vitamin A consumption (Weaver 2000).

Any child can tell you that you need to drink milk for strong bones. Calcium is an essential nutrient that is required structurally in teeth and bones as an intracellular regulator and as a cofactor for many proteins and enzymes (Weaver 2000). Research has not fully supported the assumption that milk, as a source of calcium and vitamin D, decreases osteoporotic bone loss and fracture risk in all people. Some studies have shown that calcium supplements help stop bone loss, but once the supplements stop the benefits are gone (Feskanich et al. 2003). in 2000, a review was done of 57 papers, published between 1985 and 2000, studying the effect of dairy foods on bone health. Of these papers, 53% found a nonsignificant effect, 42% showed a favorable effect and 5% showed an unfavorable effect of dairy foods on bone health (Weinsier and Krumdick 2000). A similar review done in the same year looked at the effect of calcium on bone health. It found that out of 52 studies done since 1975, all but two showed a positive effect of calcium intake on bone gain, retention or risk of fracture. All the studies in the review found calcium to be good for children’s bone health, while cross-sectional studies do not always show a positive influence on bones (Weaver 2000). What could cause the differences seen in these studies? One difference is that the first research review deals with dairy foods and the second is with calcium. The authors of the reviews did not address this discrepancy, but it may be that dairy products block calcium absorption. It is important to remember that dairy is not made of entirely calcium and calcium is found in nondairy sources, such as dark green leafy vegetables, almonds, sunflower seeds, black beans and amaranth grain. Milk is fortified with vitamin D, which is needed for calcium absorption. One study found calcium intake was not associated with fracture risk in postmenopausal women, but vitamin D was correlated with fracture risk, meaning increased vitamin D lessens the fracture risk. Vitamin A in fortified milk has been associated with an increased risk of hip fracture, so the bone strengthening benefits of calcium from dairy source may be lessened by other parts of the milk (Feskanish et al. 2003).Dietary calcium intakes by modern humans has decreased, relative to those of early humans, when cultivated grains displaced roots and tubers as staple foods. Cereal grains are fruits and consequently poor accumulators of calcium (Weaver 2000).

A fairly new and surprising health benefit from dairy has been seen in the literature recently. As the National Dairy Council (2005) put it: three servings of dairy a day in a reduced-calorie diet supports weight loss. Shamik Parikh and Jack Yanovski wrote a paper, Calcium Intake and Adiposity (2003), explaining the findings. The mechanism is still unclear, but it may be that the binding of fatty acids in the gut by dietary calcium can decrease fat absorption sufficiently to account for a similar weight change. Another study, by Michael B. Zemel (2003), suggested that dietary calcium may affect the regulation of energy metabolism and therefore the risk of obesity. A study, cited by Parkh and Yanovski, found that calcium intake could explain as much as 3% of the variability in adult body weight. This may not seem like a lot, but over time it could have a significant effect.

The National Dairy Council web site had a quiz, which I took, about assessing my diet and getting healthy with dairy. I answered questions about the amount of dairy I eat, exercise patterns, the prevalence of fruit in my diet, etc. After submitting it, the web site told me: congratulations on eating at least three servings of dairy foods each day. They cited an incredible number of sources in journals like the Journal of Obesity, American Journal of Clinical Nutrition, Obesity Research and the International Journal of Obesity and Related Metabolic Disorders. The USDA Nationwide Food Consumption Survey from 1987-1988 showed that the people with the lowest calcium intake tended to have the highest body weight. There may be a greater effect from dairy foods than might be predicted from their calcium content alone. In other words, dairy sources of calcium seem to have a substantially greater effect than supplemental fortified sources of calcium (Newby et al. 2004, Zemel 2003, Parikh and Yanovski 2003). It could be connected to calcium or it may be a distinct component.

drawing by C. Landau

Recombinant bovine growth hormone has brought a new health concern to dairy products. Without discussing the biology of the hormone in great detail, it causes increased milk production. It is a genetically modified version of their own growth hormones created by Monsanto. All milk has growth hormones; rBGH has more (Cohen 1998). The issue is extremely controversial. Many countries have banned the use of rBGH. There are questions about the safety of this product, yet regulation in the US is based on the product not the process so it is not restricted or even labeled. Many studies show that there is no difference between the rBGH milk and non-rBGH milk. While organic milk was being produced before rBGH, the concern about the safety of rBGH milk caused an increase in demand for organic milk (DuPuis 2000). Robert Cohen has written a book leading the anti-milk movement in response to rBGH and dairy in general. Milk: The Deadly Poison (1998), while at times being sensational (such as the title), goes through in great detail the less attractive and nutritious parts of dairy products. It is an interesting investigation of the health implications and possible scandal involving Monsanto and the federal government. For more information on genetically modified foods, see Sarah Roach's research project: Genetically Modified Organisms: Labeling in Northfield.

There are health benefits from milk, but perhaps not to the extant the general population believes. Especially in America, dairy is often consumed as cheese, which is high in fat. Increased cheese consumption may contribute to growing obesity. Consumers should be more aware of the type of dairy they ingest, their health needs and where to find the best source of nutrients.

drawings by C. Landau