From a young age, Americans are taught that milk is an essential component of a healthy, well-rounded diet. But new research on the long-term health effects of drinking dairy questions some age-old assumptions about milk's protective benefits.
A study published last fall in the British Medical Journal found a positive association between high milk intake and increased fracture incidence among women, contradicting the common understanding that dairy consumption reduces the risk of osteoporotic fractures. The study also revealed a correlation between significant milk consumption and higher mortality among both men and women.
Conducted by researchers at Uppsala University in Sweden, the study examined milk intake in two large cohorts of Swedes across three counties. One cohort included 61,433 women between the ages of 39-74 years at baseline; the second included 45,339 men aged 45-79 years at baseline. Both groups completed food frequency questionnaires regarding their average consumption of common foods, including milk, fermented milk, yogurt, and cheese (Michaëlsson et al. Brit Med J. 2014; 349 (7981)).
Within the female cohort, the researchers found that during a mean follow up of 20.1 years, 15,541 women had died and 17,252 had experienced a fracture, 4,259 of which were hip fractures. In the male cohort, a mean follow up of 11.2 years revealed 10,112 deaths and 5,066 fractures, with 1,166 hip fracture cases.
Women who drank three or more glasses of milk per day were found to die at nearly twice the rate of those who drank less than one glass a day, with an adjusted mortality hazard ratio of 1.93 (95% confidence interval 1.80 to 2.06).
The authors also concluded that higher milk consumption did not appear to reduce fracture risk either among women or men.
Increased Oxidative Stress
Significantly, they observed an additional positive association between high milk intake and increased levels of oxidative stress and inflammatory biomarkers. In subsamples of two additional cohorts, one male and the other female, both urine 8-iso-PGF2α, a biomarker of oxidative stress, and serum interleukin 6, an inflammatory biomarker, increased with milk consumption.
They attribute this finding to the presence of the monosaccharide sugar D-galactose in dairy products. Milk is the primary dietary source of galactose, and consuming it either by injection or in the diet, the study notes, is an "established animal model of aging by induction of oxidative stress and inflammation."
In the US, the USDA [still] recommends consuming two to three cups of dairy products per day, depending on one's age.
Milk and other dairy items have become many Americans' go-to source of calcium. From ubiquitous school cafeteria milk cartons to the FDA's former food pyramid and newer My Plate nutrition models, children and adults alike learn that milk is a necessary component of a well-balanced diet.
At birth, most people can readily digest lactose, the primary carbohydrate found in milk and an important source of nutrition during infancy. However, in most mammals, including humans,the natural production of lactase - the enzyme responsible for lactose digestion - decreases after weaning.
Notably, humans are the only species that routinely consumes milk produced by other animals. This curious fact, alongside the striking number of lactose intolerant adults, raises important questions about why we eat and drink so much dairy.
Calcium intake is certainly one motivating factor. But a long list of non-dairy calcium-rich foods reveals many other sources of this essential nutrient. Among them are green peas, chickpeas, quinoa, sesame seeds, oranges and fortified orange juice, and soybeans and other soy products such as tofu. Additionally, leafy green vegetables like kale, spinach, and collard, mustard, and beet greens are high in calcium. One cup of raw kale contains approximately 90 mg of calcium; a 3.5 cup of kale salad exceeds the amount of calcium - 300 mg - found in one cup of milk.
If dairy is required to achieve adequate nutrition, some food items may offer better choices than others. The Swedish milk study found that a high intake of fermented milk products - such as yogurt and soured milk and cheese - was actually associated with lower rates of bone fracture and mortality.
Beyond dietary considerations, many forms of exercise and healthy activity are known to support healthy bone growth and fracture prevention. Those at risk of osteoporosis should have their bone mineral density tested regularly and take efforts to reduce the risk of falls in the home. Physical activity, especially weight-bearing exercise, also helps to build and strengthen bones. Additionally, exposure to naural sunlight promotes vitamin D production and calcium absorption.
Drinking milk does not appear to be the most healthful approach to osteoporosis prevention.
Milk Ad: Against Soy, Almond, Hazelnut, Coconut Milk
Unfortunately, there is some truth to the fact that processed nut milk has its own share of health concerns. Homemade nut milk without all the extra ingredients in processed nut milk is a good choice.