Nutritional Pearls: Is Drinking Milk Good For Your Bones?
Tara is a 56-year-old woman who grew up hearing that 3 glasses of milk a day is good for her bones. She is concerned about osteoporosis, and comes to visit you to consult on her diet.
How would you advise your patient?
(Answer and discussion on next page)
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Answer: Drinking milk may be bad for your bones.
For years, if not decades, we have been told to drink our milk in order to build strong bones. Milk is a good source of calcium, vitamin D, and phosphorus—all important nutrients for bone formation and maintenance. Many people are told that they should drink at least 3 glasses a day to help prevent fractures and osteoporosis.
The problem is that research on the effects of drinking milk on bone density and the risk of fractures has been somewhat conflicting, partially because studies may differ on their focus—whether it be calcium intake (via milk and other sources), vitamin D, or total dairy consumption.
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Finally, factor in that milk is a major source of D-galactose—a byproduct of digesting the lactose in milk—that has been linked, at least in theory, to increased levels of oxidative stress and chronic inflammation (ie, greater risk of heart disease, cancers, and bone loss).
In an effort to tease out the effects of drinking milk—as opposed to fermented milk (eg, buttermilk and eating yogurt or cheese)—researchers in Sweden analyzed data from 2 major cohort studies that ran in 1987 and 1997 and included over 38,000 women and 45,000 men.1
At the start of both studies, the participants filled out a dietary questionnaire designed to assess their regular diet for the past year as well as a demographic questionnaire to collect information on education, marital status, physical activity, and smoking history.
The women were again surveyed 10 years later, and a smaller, representative group of men and women from each cohort provided urine and blood samples, enabling the researchers to analyze blood markers of oxidative stress, inflammation, and indirect measures of milk intake (to assess accuracy of the dietary recall).
The researchers were able to track the incidence of bone fractures in the participants as well as deaths and their causes. They first excluded bone fractures not related to bone density (eg, tumor-related), and factored in variables, such as caloric intake, physical activity, height, weight, smoking history, and menopausal status.
Using a control group of women who consumed <1 glass of milk per day, the data showed that women who drank >3 glasses of fluid milk per day were:
- 16% more likely to experience a fracture anywhere in their body
- 60% more likely to experience a hip fracture
- Had a 93% higher risk of death from any cause
- Had a 44% higher risk of death from cancer
On the other hand, men’s risk of fracture of any kind was not associated with their fluid milk intake, while their risk of death only increased by about 10%—mainly tied to the risk of death from cardiovascular disease.
Fermented Milk Intake
Researchers next looked at cheese and fermented dairy (ie, yogurt) products. For women, higher intakes of cheese and yogurt meant lower risks of mortality and fracture. Each increased serving reduced the risk by between 10% and 15%. There was little to no change in men.
Researchers note that the greater effects of milk intake in women may be due to the fact that they were surveyed more than once, which in turn provided greater sensitivity to their analyses. Furthermore, the findings might not be applicable to those with high rates of lactose intolerance, ethnically diverse populations, or children and adolescents.
What’s the “Take Home”?
The message for your patients is simple: Their bones will be better off with a higher intake of fermented dairy (eg, yogurt and cheese) and less drinking of fluid milk—also a pillar of the Mediterranean Diet. Additional sources of calcium may include collard greens, spinach, and kale.
1. Michaëlsson K, Wolk A, Langenskiöld S, et al. Milk intake and risk of mortality and fractures in women and men: cohort studies. BMJ. 2014;349:g6015.