Tue, 11 Sep 2007 13:00 CDT
People who take vitamin D supplements appear to have a lower risk of death from any cause, an analysis of numerous studies has found, adding to the weight of evidence suggesting that the "sunshine nutrient" confers widespread health benefits.
In an analysis of data pooled from 18 randomized controlled trials, researchers at the International Agency for Research on Cancer and the European Institute of Oncology found that subjects who took at least 500 international units of vitamin D daily had a 7 per cent lower risk of death, on average, compared with control groups given a dummy pill.
The 18 clinical trials involved a total of more than 57,000 subjects, who were followed for almost six years. Most of the studies, with participants mainly over age 65, were investigating the role of vitamin D in keeping bones strong and preventing fractures.
In the nine trials that collected blood samples, participants who took supplements had an average 1.4- to 5.2-fold higher blood level of vitamin D than those who did not, the analysis shows.
Previous studies have suggested that vitamin D deficiency may be linked to a higher risk of dying from cancer, heart disease and diabetes - illnesses that account for 60 per cent to 70 per cent of deaths in high-income countries, the authors say.
"If the associations made between vitamin D and these conditions were consistent, then interventions effectively strengthening vitamin D status should result in reduced total mortality," the authors write.
Researchers can't say for sure what it is about vitamin D that seems to improve health and apparently prolong life.
"It's still a little bit obscure," co-author Dr. Philippe Autier, chief of epidemiology and biostatistics at the Agency for Research on Cancer, said Monday from Lyon, France. "There's one area of research quite recently that showed that vitamin D had the possibility to delay, to retard, the progression of certain diseases, essentially cancer and some cardiovascular diseases."
Numerous laboratory studies have shown that vitamin D can halt the growth of cells, Dr. Autier said. "Cancer is characterized by the proliferation of cells. It looks like the vitamin D was able to . . . put a control on this, put the brake on this proliferation."
"So that's why probably vitamin D could be able to decrease the progression of the disease and explain better survival and greater life expectancy."
In June, the Canadian Cancer Society recommended that adults consider taking a vitamin D supplement of 1,000 IUs daily during fall and winter, while darker-skinned and older people should think about maintaining that daily intake year-round.
Dr. Reinhold Vieth, an expert in vitamin D and osteoporosis at Mount Sinai Hospital in Toronto, called the analysis "really interesting." By pooling results from many studies, the European researchers were able to tease out vitamin D's effect on longevity that wouldn't have been statistically relevant in a single study.
"So what it's coming along at is more and more little pieces of evidence that say it's very interesting to look at vitamin D a little bit more," said Dr. Vieth, who was not involved in the research published Tuesday in the Archives of Internal Medicine.
Two other recently published papers have shown vitamin D's apparent benefits: In one, young Finnish men who took the nutrient had half the number of respiratory infections compared with those not taking a supplement.
And in a study of older people in the Netherlands, who were followed for eight years, researchers found that those with high vitamin D levels in their blood were less likely to end up in a nursing home and less likely to die early compared to those with low blood levels of vitamin D.
"What we've been finding out over the last 10 years is that vitamin D is not a one-trick pony that just relates to bone (health), but to many biological functions that go on throughout the body and make use of vitamin D to regulate the way they work," dr. Vieth said.
"So it covers a lot of territory."
In an editorial accompanying the study, Dr. Edward Giovannucci of the Harvard School of Public Health says the meta-analysis "adds a new chapter in the accumulating evidence for a beneficial role of vitamin D on health."
"Research on vitamin D should be continued to clearly elucidate the specific benefits and optimal intakes and levels of vitamin D," Dr. Giovannucci writes. "Nonetheless, based on the total body of evidence of health conditions associated with vitamin D deficiency, abetted with the results from this meta-analysis, a more proactive attitude to identify, prevent and treat vitamin D deficiency should be part of standard medical care."
"From a broader public health perspective, the roles of moderate sun exposure, food fortification with vitamin D and higher-dose vitamin D supplements for adults need to be debated."