The Complicated Role of Calcium
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Calcium and Women
Many people are confused about the benefits and risks of calcium supplementation for midlife and older women.
A recent evidence-based Institute of Medicine (IOM) report provides guidelines to North American women about the amount of calcium they should consume and concludes that this nutrient provides critical bone benefits—but beyond consuming the Recommended Daily Allowance, there is not much to be gained.
The IOM used The Women's Health Initiative (WHI), a randomized trial of the benefits and risks of 1,000 mg of daily calcium supplements in over 36,000 postmenopausal women.
Participants with intakes greater than 1,200 mg daily at baseline did not clearly benefit from the intervention, suggesting that more is not necessarily better. The IOM set the current RDA for calcium (from food plus supplements) at 1,000 mg for women up to age 50 and 1,200 mg for those over age 50. Many women are consuming unnecessarily high doses of supplemental calcium. Instead, they should aim to meet the RDA by eating calcium-rich foods like milk, yogurt, cheese, sardines, salmon, tofu, calcium-fortified juice and cereals, broccoli, collard greens and kale.
Supplements are only appropriate if your diet does not provide the recommended amount of calcium.
Regarding other clinical outcomes in the WHI, a significant 17% increase in risk for kidney stones was noted, but the background intake of calcium was high. It is a good idea, then, to meet the RDA but not exceed it.
Calcium and Precancerous Polyps
Calcium and vitamin D, alone or in combination, have no effect on the recurrence of colorectal adenomas, according to a study published in NEJM and funded by the National Cancer Institute.
An adenoma is a type of non-cancerous tumor formed from glandular structures. These are the “polyps” commonly sought after when undergoing colonoscopy. Though benign, they can be considered precursors to colorectal cancer because over time they may transform to become malignant.
Researchers studied over 2,000 patients who had undergone complete colonoscopy during which adenomas had been found and removed. The patients were randomized to receive daily supplementation with calcium, vitamin D3, both or placebo. They then looked at the appearance of adenomas in patients undergoing follow-up colonoscopy at least a year later.
The authors had published a paper in 1999 that suggested a protective effect from calcium. Not so this time: “Daily supplementation with vitamin D3 (1000 IU), calcium (1200 mg), or both after removal of colorectal adenomas did not significantly reduce the risk of recurrent colorectal adenomas over a period of 3 to 5 years.”
Calcium and CVD Risk
Though some older studies suggested that calcium supplements have heart health benefits, calcium supplements have come under renewed scrutiny with regard to heart health following a report that men who took more than 1,000 mg of supplemental calcium daily over a 12-year period were 20% more likely to succumb to heart disease than those who didn't take the pills.
Calcium from food does not seem to raise CVD risk, but calcium supplements may raise blood calcium levels more rapidly than dietary calcium, thereby boosting risk for heart disease. It’s clearer than ever that supplements—not least of all calcium—should be approached with caution. Far better to get your nutrients from foods, not pills, to the extent possible. In certain cases, supplementation can be considered appropriate but it is important to open a dialog with your doctor before embarking on any kind of supplement regimen beyond, perhaps, a daily multivitamin.