Vitamin-D deficient older adults may be at risk for heart disease.

The epidemic of vitamin-D deficiency in the United States may be triggering an epidemic of heart disease, say researchers.

A recent study documenting heart disease and vitamin-D levels in more than 3,400 older adults saw 44 percent of its participants die in seven years, at least 21 percentage points higher than in other similar studies. Even accounting for various causes of death, vitamin-D deficiency was a “very strong predicator of death,” says Dr. Adit Ginde, the study’s lead author.

Vitamin-D deficiency has also been tied to respiratory tract infections and catching the flu in addition to heart disease, which is the leading cause of death in the United States with almost 632,000 victims in 2006.

According to the team’s previous results, roughly 23 percent of more than 13,300 participants dropped below 30 nanograms per milliliter, a level just above that which Ginde suggests is important in preventing health problems like osteoporosis.

The study is the third in a series using data from the Third National Health and Nutrition Examination Survey to document significant drops in vitamin-D levels in the last thirty years.

Ginde explains that the increase in indoor lifestyles, away from the sunlight that catalyzes vitamin-D synthesis in our skin, is likely the primary cause of the low levels. Because older adults often spend significant time indoors, they are at high risk for vitamin-D deficiency, he says. The decreased consumption of vitamin-D-heavy foods, such as fish and dairy products, has also contributed to dangerously-low vitamin-D levels, he adds.

Current supplement recommendations are not calculated to counteract the low levels the researchers are seeing, according to Ginde. While it’s hard to generalize for individual needs, he says, reaching safe levels may require a daily supplement of 1000 to 2000 international units. He adds that official recommendations (closer to 500 i.u.) are geared toward maintaining levels only one-third of those his team’s research indicates are safe.

Both individuals suffering from obesity and some thin people are at risk for vitamin-D deficiency because they both have trouble absorbing a healthy amount of the vitamin, albeit for different reasons. Because vitamin D is a fat-soluble vitamin, individuals need to be able to absorb fat and cholesterol in order to use it.

“For people who are very obese,” says Ginde, “they may need more, because it’s being stored in fat and not going into the bloodstream.”

On the other hand, he adds, thin people who do not process fat and cholesterol well will not absorb vitamin D efficiently, either. These individuals may need other sources besides supplements, such as sunlight, so that they can make their own supplies of the vitamin.

Balancing those needs with protection from the sun’s harmful ultraviolet rays may be difficult, however. While the National Cancer Institute reports a fall in the overall cancer incidence rate, the incidence of melanoma—the most aggressive skin cancer—continues to rise, with 68,720 melanoma diagnoses expected in 2009, up from nearly 54,000 in 2005. More than 8,600 of those cases will be fatal, the Institute estimates.

Ginde and his team are currently applying for funding for a five-year study to compare vitamin-D supplement levels in individuals to see if the levels have a significant effect on participant health. The most recent study appears in the Journal of the American Geriatrics Society.