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Vitamin D, Cancer, and Fractures

For that review, researchers at Tufts University reanalyzed data from more than 40 studies on vitamin D.

They set out to answer several key questions:

  • Does vitamin D, taken with or without calcium, affect the risk for cancer or broken bones?
  • Are high or low blood levels of vitamin D linked to a person’s risk for cancer or broken bones?
  • Are there harms linked to taking extra D?

Among several studies of vitamin D taken alone or with calcium, researchers say a high degree of statistical uncertainty made it impossible to tell whether taking supplements increased or decreased the risk of cancer.

With respect to fractures, data from five other studies showed that vitamin D supplementation alone, in doses ranging from 400 to 1,370 IU daily, did not appear to reduce the risk of breaking a bone.

That picture changed when calcium was combined with vitamin D.

Across 11 studies of more than 52,000 people who were followed from one to seven years, those taking 300 to 1,000 IU of vitamin D each day, along with 500 to 1,200 milligrams of daily calcium, saw their risk of breaking a bone drop by an average of 12% compared with those taking a placebo.

To answer the second question, researchers relied on studies that looked at the relationship between blood levels of vitamin D and the risk for breast, prostate, colorectal, or any kind of cancer.

There was some evidence that higher blood levels of vitamin D might protect against colon cancer. But there was no evidence that having a higher vitamin D level could protect a person against breast or prostate cancer.

In fact, some studies suggested that men who had higher levels of D had an increased risk for cancer death. The same did not appear to be true for women.

Other possible harms included an increased risk for kidney stones and bladder stones seen in one study among women taking vitamin D supplements.

Vitamin D and Heart Disease

In the second review, Irish researchers looked at the connection between vitamin D and heart health.

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