Several of you have asked us about a recently published medical study that triggered media attention. Headlines like the Washington Post’s “Study: Milk may not be very good for bones or the body” have drawn readers to a Swedish study that linked high milk intake in women to a higher risk of bone fractures and of death from other causes.
For a generation of women who have spent our adult lives trying to ensure that our diets provided enough calcium to protect us from the terrible effects of osteoporosis (weakening of bones), this was indeed disturbing news. Should women now abandon the three-servings-a-day guideline for dairy products and throw out our calcium supplements?
There is still much we don’t know about the complex relationship between calcium and vitamin D intake, bone loss, and other health risks. But one fact is certain. You need adequate amounts of calcium in your diet throughout your lifespan to reduce your risk of osteoporosis. Science has not given us clear answers about how much calcium is “enough” and which are the best sources of calcium.
Besides building strong bones and teeth, calcium is essential for regulating the heartbeat, nerve function, and blood clotting. If your diet does not provide enough calcium for these vital functions, your body will “borrow” calcium from your bones. The body’s ability to return the borrowed calcium to bones depends on many factors. Exercise, vitamins D and K, estrogen, and certain forms of vitamin A all play a role. Up to about age 30, your body builds more bone than it breaks down. Building strong bones early in life is the best osteoporosis defense. As you age, you lose bone regardless of your calcium intake or other factors. The goal then shifts toward trying to slow that bone loss.
Having enough dietary calcium is essential for slowing bone loss. The current Recommended Daily Allowance for calcium is 1000 mg up to age 50 and 1200 mg thereafter. Most dietary experts agree that the best calcium source is a well-balanced diet. Milk and other dairy products contain good amounts of calcium. Dark green leafy vegetables like collards, spinach, kale and broccoli—as well as beans, peas, and lentils—are good non-dairy calcium sources. Calcium can also come from calcium supplements. To use calcium, your body also needs vitamin D. Taking calcium alone may actually increase your risk of fractures and possibly heart-related problems. Calcium supplements often contain vitamin D. But if you are using antacids like Tums to get extra calcium, these do not.
Besides its importance for bone health, moderate calcium intake may be somewhat protective against colon cancer. On the other hand, some research has raised concern about heart-related, ovarian, or prostate cancer risk. Presently, we have no good evidence that consuming extra calcium above the recommended dietary allowance provides additional protection against fractures or any other health problem. But how much calcium is optimum for good health? The difficulty lies in providing good evidence to support our recommendations.
The Swedish study was not an “Aha!” moment; it did not provide any new answers. It did suggest, as have several other studies, that larger amounts of milk might present special health risks. Scientists have considered whether saturated fat, milk sugars, or hormones in milk products might be the cause. Although women in the Swedish group who drank more milk experienced more fractures and other health problems, this type of study has limitations. The authors acknowledged that some factor other than milk intake may have influenced the results. Like many other studies on milk consumption—with similar or totally opposite results—the new work will influence the direction of future research.
In the mean time, we recommend our patients continue to follow the current guidelines. The National Center for Health Statistics surveys estimate that only about a third of women between 30 and 50, and less than 10% of older women, reach the recommended allowance for calcium per day from food sources. Whether you need calcium supplements depends on your careful evaluation of how much calcium your diet really provides. We recommend a food journal. Besides tracking your calcium intake for a few days, it’s a powerful weight control tool. The National Osteoporosis Foundation also provides a shortcut for estimating your daily calcium intake http://nof.org/articles/542 . Above all, a well-balanced diet and other healthy choices (exercise, smoking avoidance) offer the best protection against osteoporosis later in life.