Calcium Supplements

Q:  As a woman, I try to exercise and take calcium supplements in the hope of avoiding osteoporosis. I've seen discussions on the bioavailability of the different calcium (Ca) salts, but would like to know more. Ca antacids are cheap and they taste good. But I've usually taken Ca carbonate plus magnesium (Mg) tablets (which are hard to swallow!), having read that the Mg aids in assimilation of the Ca. And the newest Ca source on the scene is the chocolate chewables. They are very tasty and I believe contain Vitamin K which is supposed to help one absorb the Ca.

Would you recommend a variety of these Ca sources? Or would just consuming the cheap and tasty chewable antacids suffice? Would they alter the stomach environment and make it too alkaline? After all, they are meant for neutralizing excess stomach acidity. What happens if you don't have that problem but are merely consuming them for their calcium?

A:  Calcium is important for maintaining strong bones and 1,000 mg a day is recommended for women under 65 who are also taking estrogen. Women not on estrogen or over 65 need 1,500 mg a day.

You can get calcium in many forms: Ca carbonate, Ca phosphate, Ca lactate, Ca gluconate, Ca citrate. You only need to take one kind of calcium supplement, and the chewable antacids are fine. Ca carbonate has the most elemental calcium (40% -- which means that 1,250 mg of Os-Cal has 500 mg of elemental calcium and 500 mg of Tums has 200 mg of elemental calcium), is cheapest, and is probably the most bioavailable. By comparison, 500 mg of calcium gluconate only has 45 mg of elemental calcium, so you would have to swallow 22 tablets a day to get 1,000 mg.

The downside of Ca carbonate is bloating, gas and constipation, but five to seven Tums a day should not interfere with your digestion.

Vitamin D aids in calcium absorption, so Viactiv, the new chocolate chewables, have 100 units of Vitamin D and 40 mcg of Vitamin K. Some Ca supplement tablets also contain Vitamin D. Pat Puestow, a registered dietician and clinical dietitian at the Diabetes Care Center at Froedtert Memorial Hospital emphasizes that people over age 50 need 400 to 600 units of Vitamin D a day, especially if they don't get enough sun exposure, for optimal calcium absorption.

Taking your calcium supplements with meals or a snack and dividing the dose will also aid in their digestion. Weight-bearing exercise also improves absorption.

"Dear Doctor" is a compilation of patient questions answered by doctors from the Medical College of Wisconsin.