Small study results supported this view. But when researchers started to crunch the data from large, prospective studies that followed people for many years, the benefits weren't so clear-cut, reports the March 2008 issue of the Harvard Health Letter.
The ambiguity led to trials to test what effect calcium might have on fracture rates. Two studies showed that calcium didn't prevent fractures ”even when taken in combination with vitamin D. Another study showed that postmenopausal women who took a calcium-vitamin D combination were no less likely to break their hip than women who took a placebo pill. And other researchers reported the results from a meta-analysis of studies on calcium that found no connection between high calcium intake and lower hip fracture risk.
While a certain level of calcium intake is undoubtedly important to keeping bones strong, amounts above that level might not do much good, notes the Harvard Health Letter. One reason some of these studies on supplements may not have shown a benefit is because the study participants were already getting over 1,000 milligrams (mg) of calcium daily through diet.
The bottom line: According to current recommendations, Americans over 50 are supposed to get 1,200 mg of calcium daily, but 600 mg is probably enough for most people to keep their fracture risk low. Still, because extra calcium might be protective against colon cancer, a daily intake of 600 to 1,000 mg is a reasonable goal.
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Zhang and his colleagues tested the ability of the concentrate to prevent bladder tumors in five groups of rats. The first group acted as a control, while the second group was given only the broccoli extract to test for safety. The remaining three groups were given a chemical, N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) in drinking water, which induces bladder cancer. Two of these groups were given the broccoli extract in diet, beginning two weeks before the carcinogenic chemical was delivered.
In the control group and the group given only the extract, no tumors developed, and there was no toxicity from the extract in the rats.
About 96 percent of animals given only BBN developed an average of almost two tumors each of varying sizes. By comparison, about 74 percent of animals given a low dose of the extract developed cancer, and the number of tumors per rat was 1.39. The group given the high dose of extract had even fewer tumors. About 38 percent of this high-dose group developed cancer, and the average number of tumors per animal was only .46 and, unlike the other animals, the majority were very small in size.
The study was funded by the Vital Vegetables Research Program of Australia and New Zealand, the National Cancer Institute and the Roswell Park Alliance Foundation.
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