Consumers should rely on food first to get the calcium needed by the body because scientists still don't know the long-term effects of high doses of vitamin and mineral supplements, warns the American Society for Bone and Mineral Research.
Daily intake of dietary calcium is recommended by physicians to prevent osteoporosis, a bone-thinning disease that strikes one in four older American women.
"Women lose bone mass at the rate of about 1% a year beginning at age 20," said Dr. Bess Dawson-Hughes, a Tufts University bone researcher. "A woman may lose 30% of her skeletal mass when she reaches menopause or at age 50."
At menopause, the rate of loss is accelerated, so that by 60, a woman may have lost close to one-half of her skeletal mass, resulting in extremely fragile, brittle bones--a condition known as osteoporosis.
Keep Intake Levels High
"Therefore, it is essential that younger women, in their 20s, 30s and 40s, keep their intake of calcium as high as possible--at least 1,000 milligrams a day," she said.
Studies show that women usually consume about 500 to 700 milligrams of calcium a day--only about one-half of what they need to maintain adequate calcium stores.
"Milk and other dairy products provide 75% of the calcium in the American diet and they contain the Vitamin D necessary to aid in the absorption of calcium," she said.
Other calcium sources are sardines, salmon with bones, collards, tofu, spinach, broccoli and bok choy.
To fill in the gaps, many women turn to calcium supplements, which contain no nutrients, to aid calcium absorption. According to Dawson-Hughes, the long-range effects of high-dosage supplementation are unknown.
"We should increase dietary intake of calcium from food as much as possible and use supplements only as a secondary source," she said.
Dawson-Hughes recommends that women past the age of 40 consume 1,500 milligrams of calcium a day. Those younger than 40 should consume 1,000 milligrams daily.
For a standard dietary measure, one eight-ounce glass of low-fat milk contains about 290 milligrams of calcium, and one ounce of Swiss cheese has 262 milligrams. Dawson-Hughes' recommendations translate into about three milk group servings a day for premenopausal women, and four for postmenopausal women.
Dawson-Hughes also cautioned against high-protein diets, which increase the amount of calcium excreted in the urine, further inhibiting the nutrient's absorption.
The ASBMR offers the following osteoporosis prevention guidelines for all females:
--Get plenty of exercise; daily running or brisk walking are the most beneficial.
--Eat calcium-rich foods every day.
--Avoid large amounts of Vitamin A (greater than 5,000 international units a day) or Vitamin D (greater than 1,000 international units a day) unless medically indicated and prescribed by a physician. Daily exposure to sunlight or a quart of milk provides adequate Vitamin D intake.
--Avoid cigarette smoking.
--Take precautions to prevent falls, especially the frail and the elderly.
--Discuss the potential use of estrogen replacement therapy with a physician.