Adults with low blood levels of vitamin D are 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.

Researchers 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. During a follow-up of about 27 years on average, 640 participants (of which 358 were men) died from heart disease and another 293 (122 men) died due to 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. There was a particularly striking association between vitamin D levels and stroke deaths - low vitamin D levels doubled the risk, compared with having the high vitamin D levels. Allowing for age, gender, other demographic factors, alcohol intake, smoking, physical activity, and season in which vitamin D levels were obtained did not significantly alter these associations.

In the above study, vitamin D levels were substantially lower than levels thought to be sufficient, and somewhat lower than those reported in previous studies. However, there is no absolute consensus as to what is the optimal range of vitamin D. Therefore, further studies are needed to confirm and find explanations for low levels of vitamin D causing heart disease or stroke.