Many Americans have become so effective at covering themselves from the sun that they don't get enough vitamin D, which may be putting them at increased risk not only for cardiovascular disease but for depression.

That's the finding of a new study of more than 27,000 patients tracked by researchers at Intermountain Medical Center, who found that healthy levels of vitamin D contribute to a strong and healthy heart.

They also found that inadequate vitamin D levels may significantly increase the risk of stroke, heart disease and death — even among those who've never had heart disease.

The study's findings were presented Monday at the American Heart Association's annual scientific conference in Orlando, Fla.

Researchers also found a lack of vitamin D may contribute to depression in both men and women.

"This was a unique study because the association between vitamin D deficiency and cardiovascular disease has not been well-established," said Dr. Brent Muhlestein, director of cardiovascular research of the Heart Institute at IMC and a lead researcher on the study.

"Its conclusions about how we can prevent disease and provide treatment may ultimately help us save more lives."

Muhlestein said the research team began thinking about recent vitamin D studies in conjunction with the fact that kidney-failure patients usually die of heart disease or heart attacks, rather than kidney failure.

Those patients also "don't make enough vitamin D," so when doctors were able to supplement the kidney patients with the vitamin, "they're less likely to die of heart attacks."

Researchers working on a variety of studies with vitamin D had discovered that "it's a co-factor in more than 200 different processes in the body," including glucose metabolism, as well as being a component of managing blood pressure and in the body's inflammatory response. "All three of those have been found to be critically linked to heart disease," he said.

"We're not the first to have ever looked at this, but I think this is the largest general-population study" on the topic, he added.

While researchers have documented the association between vitamin D deficiency and heart disease, they still don't know whether it's a "cause-and-effect" relationship at this point, he said.

Dr. Heidi May, one of the study's co-authors, said there is also a strong association between vitamin D deficiency and the risk of developing depression. From the larger database, researchers examined those who were low on the vitamin who also had cardiovascular disease and found that 8,600 of them had about a 40 percent higher risk for depression.