January 8, 2008
Study Ties Heart Ills, Vitamin D Deficiency: Northerners May Face Greater Risk in Lack of Sun
Low levels of vitamin D, a chronic problem for many people in northern latitudes areas such as Wisconsin, were associated with substantially higher rates of heart disease and stroke, according to the latest study in a growing amount of research suggesting that vitamin D deficiencies might be at the root of a variety of serious health problems.
Indeed, a second study published online Monday in another journal concluded that people who got increased levels of sun exposure had a better chance of surviving various cancers than those who got limited sun exposure.In one of the strongest studies to date linking the vitamin to cardiovascular disease, researchers followed 1,739 members of the Framingham Offspring Study for more than five years.
They found the rate of cardiovascular disease events such as heart attacks, strokes and heart failure were from 53% to 80% higher in people with low levels of vitamin D in their blood.
"This is a stunning study," said John Whitcomb, medical director of the Aurora Sinai Wellness Institute in Milwaukee. He was not involved in the study.
Whitcomb said the study bolsters the idea that people living in Wisconsin and other northern latitude areas should be supplementing their diet with vitamin D pills from October through March.
Whitcomb noted that other than eating lots of fatty fish, it is nearly impossible to maintain optimal vitamin D levels through diet alone. Sun exposure and taking vitamin D supplements are the only proven methods, he said.
"We were designed to live in sunshine," Whitcomb said. "Every year we go through this five-month stress test."
Because the study followed patients after their vitamin D levels were measured, it is more rigorous in design than other research that merely found a retrospective link between vitamin D levels and cardiovascular disease, said Denise Teves, an assistant professor of medicine at the Medical College of Wisconsin in Wauwatosa who was also not involved in the study.
"It makes perfect sense," she said.
In patients she evaluates for possible osteoporosis at Froedtert Hospital and the Zablocki Veterans Affairs Medical Center, up to 90% have insufficient levels of vitamin D, Teves said.
Smooth muscle cells
Teves noted there are several reasons why vitamin D might help prevent cardiovascular disease.
She said cells that line the arteries of the heart have vitamin D receptors. Low levels of vitamin D can lead to a proliferation of smooth muscle cells in those blood vessels, which, in turn, can lead to blockages and stiffness in arteries.
In addition, more vitamin D can lead to less inflammation in arteries. It also has been linked to reduced blood pressure.
Teves said that while the current recommendation for adults is to get about 400 international units of vitamin D a day, an optimal level might be from 800 to 2,000 international units.
However, other vitamins have shown initial promise in preventing cardiovascular disease only to fizzle out when randomized clinical trials were done, said Matthew Wolff, chief of cardiovascular medicine at the University of Wisconsin Hospital and Clinics in Madison.
Wolff, who was not involved with the study, said that people who take vitamins tend to lead healthier lives than those who don't and it is hard determine whether it is the vitamin or the lifestyle that is the root of the health benefit.
Still, Wolff said, there is a great deal of biochemical evidence that explains why vitamin D might be beneficial.
"We can't assume there is a therapeutic benefit from taking the vitamin," Wolff said. "It's just intriguing."
However, researchers say there may be one significant difference between vitamin D and vitamins such as C and E and folic acid, which have failed to show a benefit in reducing cardiovascular disease risk in randomized trials.
For much of history, humans lived near the equator and were exposed to higher amounts of ultraviolet light, resulting in higher levels of vitamin D in their bodies, said Thomas Wang, lead author of the cardiovascular risk and vitamin D study, which was published online Monday in the journal Circulation.
"The levels we see today in developed countries are relatively unusual, especially from an evolutionary standpoint," said Wang, an assistant professor of medicine at Harvard Medical School.
One-third to one-half of otherwise healthy, middle-aged to older adults have low levels of vitamin D in the United States, the study says.
The study found a significant reduction in cardiovascular disease risk in people who had more than 15 nanograms per milliliter of 25-dihydroxyvitamin D -- the form of vitamin D stored in blood -- compared with those who had less than that.
Wang said the benefit might have been even greater if the study had compared 15 nanograms per milliliter or less with at least 30 nanograms per milliliter, which many researchers believe is the optimal level of vitamin D.
Wang said his study doesn't prove that taking vitamin supplements reduces heart attacks and strokes. That can only be done with a large clinical trial in which vitamin D is compared with a placebo.
However, until such studies are done, there is little risk for adults who take up to 2,000 international units a day, he said.
Over the last several years, numerous studies have found links between low levels of vitamin D, not just with bone health, but in various cancers, the flu, diabetes, multiple sclerosis and other neurological disorders.
The amount of vitamin D produced in the body as the result of sunlight is 3.4 times to 4.8 times greater below the equator than in the United Kingdom and Scandinavia, according to a separate analysis published online Monday in the Proceedings of the National Academy of Sciences.
The researchers found that survival from various internal cancers improved with greater amounts of sun exposure.
"It's at least a 30 percent reduction" in mortality, said senior author Richard Setlow, a biophysicist with the Brookhaven National Laboratory in Upton, N.Y. "It depends on the cancer."
Most of the work on the study was done in Norway.