Calcium and Vitamin D: Necessary for Bone Health?

The Family Health Guide

Recently, news stories reported that studies found that daily calcium and vitamin D supplements may not help older women protect their bones or prevent colon cancer — at least not as much as we thought they would.

Researchers for the Women's Health Initiative (WHI) looked at more than 36,000 healthy women ages 50–79. Half of the women took 1,000 mg of elemental calcium and 400 IU of vitamin D each day. The other half took a sugar pill (placebo). After seven years, the women taking the supplements showed slightly better bone density in their hips. They also had fewer hip fractures, but the results could have occurred by chance: Protection against hip fractures, a key goal of improving bone density, was not proven.

So, should women ditch their TUMS, calcium chews, and vitamin-D–fortified dairy foods?

Not necessarily.

Any large, carefully conducted randomized trial, such as this one, provides strong evidence that applies to people who are just like those in the study—and may not apply to women who are different in important ways. For example:

Many previous studies of calcium and vitamin D have been focused on women who are known to have low bone density, or risk factors for osteoporosis, however, in this study many of the women had normal bone density to begin with and no risk factors.

The average woman in this study was in her early 60s; so the results may not apply to women entering menopause.

The average woman in the study was taking hormone therapy, which increases bone density.

Finally, the amount of vitamin D used in this study (400 IU) may have been inadequate

It is also important to emphasize that randomized trials like this one achieve their power through the act of randomly assigning some people to the real treatment and other people to a placebo. The results are properly interpreted by comparing the patients assigned to the real treatment to those assigned to placebo. In this study, only 59% of the women assigned to take calcium and vitamin D actually took the full intended dose. And most of the women assigned to take the placebo pill were already getting nearly the recommended amount of daily calcium through their diets and vitamins/supplements when the study started. In other words, the women assigned to take the placebo pill were not necessarily deprived of sufficient calcium.

So, if you are different from the average woman in this study the results of this study may not apply to you.

Women who want to protect their bones can focus on the strategies we know work:

Get regular weight bearing exercise. Examples include walking, stair climbing, riding a stationary bike that offers resistance, and weight training.

Get enough vitamin D. You need vitamin D in order to absorb calcium. For many people, the largest source of vitamin D is their own skin. Ten to fifteen minutes of sun exposure a few times per week is usually plenty.

Few foods contain vitamin D. If you live in the more northern parts of the northern hemisphere or southern parts of the southern hemisphere and don't get much sun, consider a supplement. In this study, 400 IU did improve bone density and decreased hip fracture risk. Other studies suggest that 800 IU is right dose. Don't double up on your multivitamins, though, to get enough vitamin D. You'll get too much of other vitamins, particularly A which can compete with vitamin D.

Don't over do it with the vitamin D. Keep it under 1,000 IU and definitely not more than 2,000 IU daily. High doses of vitamin D and calcium can cause problems, such as kidney stones.

Limit intake of vitamin A, particularly in the form of retinol. Too much vitamin A can lower bone density.

Eat a diet rich in calcium. Low fat dairy products and fish are healthy dietary sources of calcium. Just how much calcium women need remains unclear. Most women can achieve adequate daily calcium intake with by eating a variety of calcium-rich foods.

April 2006 update