In people with low blood levels of vitamin D, boosting them with supplements more than halved a person's risk of dying from any cause compared to someone who remained deficient, in a large new study.
Analyzing data on more than 10,000 patients, University of Kansas researchers found that 70 per cent were deficient in vitamin D and they were at significantly higher risk for a variety of heart diseases.
D-deficiency also nearly doubled a person's likelihood of dying, whereas correcting the deficiency with supplements lowered their risk of death by 60 per cent.
"We expected to see that there was a relationship between heart disease and vitamin D deficiency; we were surprised at how strong it was," Dr. James L. Vacek, a professor of cardiology at the University of Kansas Hospital and Medical Center, told Reuters Health.
"It was so much more profound than we expected."
Vitamin D deficiency has been linked to a range of illnesses, but few studies have demonstrated the reverse -- that supplements could prevent those outcomes.
Vacek and his team reviewed data from 10,899 adults whose vitamin D serum levels had been tested at the University of Kansas Hospital, and found that more than 70 per cent of the patients were below 30 nanograms per milliliter, the level many experts consider sufficient for good health.
After taking into account the patients' medical history, medications and other factors, the cardiologists found that people with deficient levels of vitamin D were more than twice as likely to have diabetes, 40 per cent more likely to have high blood pressure and about 30 per cent more likely to suffer from cardiomyopathy -- a diseased heart muscle -- as people without D deficiency.
Overall, those who were deficient in D had a three-fold higher likelihood of dying from any cause than those who weren't deficient, the researchers reported in the American Journal of Cardiology. Moreover, when the team looked at people who took vitamin D supplements, their risk of death from any cause was about 60 per cent lower than the rest of the patients, although the effect was strongest among those who were vitamin D deficient at the time they were tested.
The study does not prove that vitamin D is the cause of the effects seen -- other factors, like disease, could be responsible both for the differences in health and the differences in vitamin D levels, for instance.
Previous research has indicated that many Americans don't have sufficient levels of vitamin D, however. The latest National Health and Nutrition Examination Survey estimated that 25 per cent to 57 per cent of adults have insufficient levels of D, and other studies have suggested the number is as high as 70 per cent.
Vacek said he believes so many people are deficient because we should get about 90 per cent of our Vitamin D from the sun and only about 10 per cent from our food. The human body makes vitamin D in response to skin exposure to sunlight.
Certain foods, like oily fish, eggs and enriched milk products are also good sources of D. A sufficient amount of Vitamin D absorption from the sun would require at least 20 minutes of full-body exposure each day in warmer seasons, and most people aren't outside enough, Vacek said.
In the northern United States and throughout Canada, experts say the sun isn't strong enough during the winter months to make sufficient vitamin D, even if the weather was warm enough to expose the skin for a long time.
It means that adults should consider getting their Vitamin D levels checked through a simple blood test, Vacek said, and take vitamin D supplements. Generally, Vacek recommends that adults take between 1,000 to 2,000 international units (IU) of Vitamin D each day.
"If you're not deficient, Vitamin D is not a magic pill that will make you live longer," Vacek said.
"Its benefit is in people who are deficient. If you're low, it makes sense to be put on replacement therapy and have a follow-up a couple months later to make sure your levels come up."