Calcium and Vitamin D: Necessary for Bone
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
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
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
Finally, the amount of vitamin D used in this study (400 IU) may have
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
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
Get regular weight bearing exercise. Examples include walking, stair
climbing, riding a stationary bike that offers resistance, and weight
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
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