Calcium and vitamin D help prevent osteoporosis


June 08, 1993|By Dr. Genevieve Matanoski | Dr. Genevieve Matanoski,Contributing Writer

Like so many of my women colleagues and friends, I seem to get just a tiny bit shorter every year. The villain in this is clearly osteoporosis. According to the National Osteoporosis Foundation, more than 50 percent of all women over 45 have osteoporosis of the spine. Virtually all women over 80 have at least some osteoporosis. With women now living to an average age of 79 years, most of us can anticipate osteoporosis as one problem of aging.

This can become particularly alarming when one considers that the most common cause of fractures for women over 80 is weakened and brittle bone caused by osteoporosis.

Many women, particularly those over 45, ask me whether they should be taking calcium supplements. Dr. Benjamin Caballero, director of the Center for Human Nutrition at the Johns Hopkins School of Public Health, gave me the current thinking on this important issue.

Q: What exactly is osteoporosis?

A: Osteoporosis is the thinning of the bone mass -- actually, bone loss, just as balding is hair loss. Bones are not an inert substance: Calcium is constantly being deposited and removed from the skeleton, and this determines its size and density, what we call "bone mass." Maximal bone mass occurs around age 25-30 and remains stable until 35-45. From then on, both men and women lose bone mass at a rate of about 0.2 percent to 0.5 percent per year. For women, however, this rate increases dramatically five to 10 years before menopause, to around 5 percent per year. This increased loss continues for 10 or more years after menopause and causes marked fragility in the bones.

Q: How can I prevent it?

A: As with so many things, the basic message is exercise, diet and lifestyle. The best way to prevent bone loss is to follow a regular, moderate exercise program -- exercise is a physiological stimulus for bone growth -- eat a lifetime healthy diet rich in calcium and avoid excessive amounts of alcohol and caffeine consumption, which tend to accelerate bone loss. Moderation on protein intake also helps, since a diet high in protein may increase the loss of calcium through the urine.

Q: How do I know if I am at risk for osteoporosis?

A: The two most important determinants of risk (besides genetic factors) are, first, the peak bone mass a woman achieves by the time she is 20 to 30 years old and, second, the rate of loss before and during menopause. Therefore it is important to maximize bone mass while you are young. Women over 40 can also benefit from calcium supplements.

Q: What role do calcium and vitamin intake play in preventing osteoporosis?

A: Adequate calcium intake is critical to ensuring maximum bone mass in younger women and to maintaining it during and after menopause.

Adolescents should make sure they get at least 1.2 grams of calcium daily. As we age our intestines are less able to absorb calcium, so older women may need to take higher amounts of calcium. However it is not entirely clear whether higher doses of calcium actually prevent bone loss in older women. It seems that the main culprit for increased bone loss in women is the lack of estrogen, and this can be prevented by estrogen supplements. Vitamin D is also essential for calcium absorption and bone formation.

Q: Should I take both calcium and vitamin D supplements?

A: Yes. There are not many foods rich in calcium other than dairy products, which have a downside because of their high levels of cholesterol and fat. Calcium supplements are therefore a good way to add calcium to your diet. The recommended daily intake for adults is 800 mg. Women over 40 can safely consume 1,200 to 1,500 mg per day, though this may cause constipation or occasional cramps in some people.

As for vitamin D, most people should get enough from sunlight. However, elderly people who spend little time outdoors tend to have low levels and should take supplements.

Dr. Matanoski is a physician and professor of epidemiology at the Johns Hopkins School of Hygiene and Public Health.

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