For a long time, the need for eating calcium to strengthen bones was almost unquestioned. But when results from the Women’s Health Initiative (WHI) trial were released earlier this year, some people wondered whether trying to increase calcium consumption was worth the effort.
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A more detailed look at the results provides several take-home lessons. Giving up calcium is not one of them.
In the WHI studies, more than 36,000 women aged 50 to 79 were randomly assigned to take either a supplement of 1,000 milligrams (mg) of calcium and 400 International Units (IU) of vitamin D or a placebo each day for about seven years. Although the hip bone density of the women who took supplements improved only slightly and their risk of fractures was the same, the data revealed important lessons.
1. More calcium helps only if you don’t get enough. Half of all older American women eat less than 650 mg of calcium from food each day, although 1,200 mg is recommended for all adults after age 50. At the beginning of this study, however, almost one-third of the women in both groups took calcium supplements of at least 500 mg daily.
Researchers did not ask the women to stop. “Since the women in the supplement and placebo groups both started the study consuming about 1,150 mg of calcium a day,” notes Jeri Nieves, PhD, Assistant Professor of Epidemiology at Columbia University, “this ended up being a comparison of 1,000 mg versus 2,000 mg of calcium a day not inadequate versus adequate calcium.”
2. You may need more vitamin D. Current federal recommendations for adults aged 51 to 70 still call for the 400 IU daily used in these studies. Yet research now shows that 700 to 1,000 IU of vitamin D a day appears necessary to reach the most healthy blood levels of vitamin D. A daily intake of 400 IU is now considered inadequate to prevent fractures.
3. You need consistently high nutrients for benefits. By the end of the trial, only 59 percent of women were still taking their pills as instructed. The women who actually took their calcium and vitamin D supplements had 29 percent fewer hip fractures.
4. Develop a cancer-protection strategy you can follow. Although no significant difference was seen in cancer risk, tumor characteristics, or reports of polyps in this study, a seven-year study is not enough time to see the effects on a disease that typically develops over 10 to 20 years. It should be noted, however, that women who started the study with low blood levels of vitamin D developed more than twice as much colorectal cancer as those with the highest blood levels.
This evidence supports the idea that long-term vitamin D status may affect our risk for this cancer. The women with the lowest blood levels of this vitamin also tended to show the most benefit from supplements.
Longer usages and higher doses than now recommended might have produced truly significant effects in the women who lacked vitamin D.
Another new study of more than 45,000 Swedish men supports adequate consumption of calcium. Men in the top half of calcium consumption were 27 to 32 percent less likely to develop colorectal cancer than those who consumed less. Although a few but definitely not all studies have linked excessive calcium or dairy product consumption with a possible increase in prostate cancer, the colorectal protection in this study occurred when men ate at least an average of the currently recommended 1,200 mg per day.
5. For bone health and lower colon cancer risk, meeting current recommendations for calcium and vitamin D is a good start. For optimal wellness protection, add regular exercise, weight control, limited sodium intake and a balanced, mostly plant-based diet with plenty of fruits, vegetables and whole grains to your daily habits.
Nutrition Notes is provided by the American Institute for Cancer Research in Washington, D.C.
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