Doctors have long known that vitamin D is essential to good health. Get enough of it and it ensures strong bones and teeth. But a new study this week suggests an even more extraordinary benefit: a lower risk of death.
The new paper, published in the Sept. 10 issue of the Archives of Internal Medicine, is a meta-analysis of 18 previously published studies on the vitamin. None of the original experiments was specifically designed to study how vitamin D affects mortality the trials involved conditions such as bone fractures, bone mineral density, congestive heart failure and colorectal cancer but all of them tracked participants' death data. Overall, researchers found, people who took daily vitamin D supplements were 7% less likely to die during the study from any cause than people who didn't.
The study's authors still don't know exactly how the vitamin may reduce people's death risk, but their findings are in line with a spate of recent research linking the vitamin to a wide range of health benefits. Not only does it promote calcium absorption and bone maintenance, but vitamin D also appears to stimulate the immune system, inhibit cellular proliferation and spur cell differentiation in turn, those processes could reduce the aggressiveness of cancer tumors or keep artery-clogging plaques from growing. Indeed, studies have suggested that low levels of vitamin D may be associated with a higher risk of death from certain cancers, heart disease and diabetes.
The current analysis looked at data on 57,311 participants, most of whom were middle-aged or elderly and in generally good health. Those in intervention groups took daily doses of vitamin D ranging mostly from 400 IU to 833 IU per day, with a study sizeadjusted mean intake of 528 IU a day. Compared with people who weren't given supplements, the test groups had up to a five times greater blood level of vitamin D and a significantly reduced risk of death. Though there's no medically recommended optimum level of the vitamin, "throughout human evolution when the vitamin D system was developing, the 'natural' level... was probably around 50 ng/mL or higher," writes Dr. Edward Giovannucci, a professor of nutrition and epidemiology at the Harvard School of Public Health, in an accompanying editorial. "In modern societies, few people attain such high levels, and levels below 10 ng/mL or 15 ng/mL are not uncommon."
If people can't get enough natural vitamin D from food or sun exposure, which synthesizes it in the skin, then daily supplements may be a good alternative and the current study shows that an intake of up to 800 IU a day is safe. In the 18 studies that researchers analyzed for the current report, none of the participants taking supplements even at a 2,000 IU daily dose surpassed the 50 ng/mL mark. According to Giovannucci, people should reasonably shoot for levels of 30 ng/mL to 40 ng/mL, and doctors should consider testing patients who are at risk for deficiencies in vitamin D.