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Research points to link between low vitamin D, mortality

Date:2008-7-22 12:43

Canwest News Service

Published: Monday, June 23, 2008

In the latest run of good news for vitamin D comes a new study showing that people with higher levels of the "sunshine" vitamin were less likely to die from any cause - including cardiovascular disease, the No. 1 killer of Canadians - after eight years of tracking.

The finding held even when researchers took coronary artery disease, exercise and other factors into account.

Low vitamin D levels "can be considered a strong risk indicator for all-cause mortality in women and in men," researchers report Tuesday in the journal Archives of Internal Medicine.

By the time the paper had been accepted for publication, the team had dug deeper and found low vitamin D status "had other significant negative effects in terms of incidence of cancer, stroke, sudden cardiac death and death of heart failure," lead author Dr. Harald Dobnig, of the Medical University of Graz in Austria, said in an e-mail.

It's still not "ultimate proof" of the harmful effects of too little vitamin D, he says. "But the evidence is just becoming overwhelming at this point."

Researchers can't rule out that sicker patients had lower vitamin D levels and, therefore, were already at an increased risk of dying to begin with.

But, "this was not a bedridden, immobile or very sick population that we studied," Dobnig says. People with an acute illness other than cardiac disease were excluded from the study.

"Low levels of vitamin D may carry a potential health risk," Dobnig says. "Physicians should be aware of the widespread problem of low vitamin D status."

He says those at high risk for vitamin D deficiency - including the elderly, nursing home residents and people who work night shifts or spend a lot of time indoors - should take 800 international units of vitamin D3 daily. "Whether we can go to higher (or even much higher) doses is unclear at the moment."

About 50 to 60 per cent of older adults in North America are low in vitamin D, and it also seems to be a widespread problem in children as well.

In the past year, studies have linked low vitamin D to an increased risk of cancers, notably breast, colon and endometrial cancers, as well as multiple sclerosis - a disease more common in northern countries. And, in back-to-back studies this month, researchers reported that men with too little vitamin D appear to be at increased risk of heart attacks, while colon cancer patients with abundant vitamin D were less likely to die during followup.

The new study is based on 3,258 consecutive patients scheduled for an angiogram - an X-ray to check for abnormalities in the arteries - at a medical centre in Germany between 1997 and 2000.

Before and after the test, their blood was measured for vitamin D3, and a compound called 25-hydroxyvitamin D, considered the best indicator of a person's vitamin D status.

After an average followup of nearly eight years, 737 people (about 23 per cent) had died, including 463 who died of cardiovascular causes.

People who had 25-hydroxyvitamin D levels in the lower half of the vitamin D range were up to twice as likely to die during the followup period compared with those in the highest. Similar results were found in people with the lowest levels of vitamin D3.

Overall, two-thirds of the patients had coronary artery disease. But whether or not they had signs of congestive heart failure or artery disease, low levels of vitamin D were "always significantly associated" with a higher risk of death, Dobnig says.

People with low vitamin D had signs of inflammation and oxygen-related damage to cells, "which all points towards a higher vascular risk profile," Dobnig says.

"This is the first study showing a significant association between serum (blood) vitamin D levels and risk of all-cause and cardiovascular mortality," he says.

But it's just that - an association, cautions Dr. Beth Abramson, a cardiologist at St. Michael's Hospital in Toronto and spokeswoman for the Heart and Stroke Foundation.

People with higher vitamin D levels tended to be healthier and more fit. Rather than focus on a "trendy risk factor," Abramson says Canadians should be aware of traditional risk factors for heart disease, such as high blood pressure, high cholesterol, smoking, diabetes and a family history of the disease.

Roughly 80 to 90 per cent of 25-hydroxyvitamin D is derived from exposure to sunlight, the rest from foods, such as fatty fish and eggs, Dobnig says. But in Canada, our bodies can't make the vitamin under weak fall and winter sunlight, and experts say more research is needed about the amount of sunlight exposure needed to achieve the optimum vitamin D levels.

As well, sun exposure increases skin cancer risk. "Don't sit and bake. There's no evidence that's helping you in the long run," Abramson says.

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