Low vitamin D levels in the body may be deadly, according to a new study hinting that adults with lower, versus higher, blood levels of vitamin D may be more likely to die from heart disease or stroke.

Vitamin D is an essential vitamin mostly obtained from direct sunlight exposure, but also found in foods and multivitamins.

Dr. Annamari Kilkkinen, at the National Institute for Health and Welfare in Helsinki, Finland, and colleagues compared blood levels of vitamin D and deaths from heart disease or stroke over time in 2,817 men and 3,402 women in Finland.

At enrollment, participants were just over 49 years old on average, and had no indicators of cardiovascular disease, the researchers note in the American Journal of Epidemiology.

During follow-up of about 27 years on average, 640 of the participants (358 men) died from heart disease and another 293 (122 men) died from stroke.

Compared with participants' with the highest vitamin D, those with the lowest had 25 percent higher risk of dying from heart disease or stroke, Kilkkinen noted in an email to Reuters Health.

There was a "particularly striking association" between vitamin D levels and stroke deaths, the researcher noted, in that having the lowest vitamin D seemed to confer "twice the risk," compared with having the highest vitamin D.

Allowing for age, gender, and other demographic factors, plus alcohol intake, smoking, physical activity, and season in which vitamin D levels were obtained did not significantly alter these associations.

In this study, vitamin D levels were "substantially lower" than levels thought to be sufficient, and "somewhat lower" than those reported in previous studies in other European and American populations.

However, there is no "absolute consensus" as to what the optimal range of vitamin D should be, the investigators note. Also, it's not known whether low vitamin D actually causes increased risk for heart disease or stroke. Clearly, further study is needed, they conclude.

SOURCE: American Journal of Epidemiology, October 15, 2009

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November 3, 2009