Low Vitamin D Levels Linked to Greater
Risk of Heart Attacks in Men
From Tuesday's Globe and Mail
June 10, 2008 at 9:59 AM EDT
Having low levels of vitamin D is associated with a doubling of the risk of heart attacks in men
and an even greater risk of dying from the cardiac condition, according to a new study.
The findings, published yesterday in the journal Archives of Internal Medicine, may help shed light on why many people with no known risk factors - such as high blood pressure or smoking - inexplicably develop heart attacks. It also suggests it may be possible to reduce the incidence of the often fatal condition by popping an inexpensive pill that is widely available in pharmacies and supplement stores.
"It's an important finding," says Edward Giovannucci, professor of nutrition and epidemiology
at the Harvard School of Public Health in Boston, one of the researchers.
"It does indicate that even individuals without the standard risk factors for heart disease
may be at somewhat higher risk if they have lower vitamin D levels," he said.
New findings suggest it may be possible to reduce the incidence of heart attacks with vitamin D.
Dr. Giovannucci said vitamin D may be beneficial by reducing the buildup of plaque in arteries, one of the causes of heart attacks.
The possible link between vitamin D insufficiency and heart attacks is among a growing number of recent medical observations about the nutrient, which is often dubbed the sunshine vitamin because it can be created in people's skin when it is exposed to strong ultraviolet light, in addition to being available in a pill form.
In the past year, other research has linked low vitamin D levels to cancer, diabetes, and heart disease, among other
chronic ailments, and Health Canada has recently indicated it intends to have the various health claims studied.
The new finding may help explain why heart attack incidence has a peculiar distribution. It rises during the winter months, and
is more common in northerly countries, such as Canada, regardless of whether people have other proven risk factors.
The vitamin seems to explain the trend because it has a strong seasonal fluctuation, falling in people's
bodies during fall and winter when sunlight is too feeble to make any of it in the skin.
Vitamin D has also recently been found to offer some protection against respiratory infections, another heart attack risk factor.
Although the study doesn't prove vitamin D caused the reduction in heart attack risk, it is considered by some medical researchers as strong circumstantial evidence of a connection. A more conclusive judgment would take a drug-style clinical trial.
In the study, researchers compared levels of the nutrient in the blood of 454 male doctors and other health-care
professionals in the United States who had heart attacks with those of a group of 900 of their colleagues similar in age,
smoking habits and other factors who did not have an attack.
The men were chosen from a continuing research projected conducted at Harvard known as the Health Professionals Follow-up Study,
which began in 1986 to scrutinize nutritional factors among 51,000 dentists, doctors and other medical practitioners for clues
about the causes of cancer and heart disease.
Most of the blood samples were drawn from 1993 to 1995. The participants were followed for 10 years.
Only 23 per cent of the men had sufficient levels, defined as circulating vitamin D of 75 Nano moles for each litre of blood or more.
Those with less than 37.5 nmol a litre were deemed to have low amounts.
Those in the low category had a 109 per cent higher risk of a heart attack than those whose
levels were sufficient, after adjusting for other risk factors, such as smoking.
According to the study, each 2.5-nmol-a-litre increase in vitamin D levels led to a 2.1-per-cent
decrease in heart attack risk and a 4.3-per-cent decrease in the risk of a fatal attack.
In Canada, vitamin D blood tests are free to consumers and covered by provincial health insurance plans.
Dr. Giovannucci estimated that to move from the low category to sufficient would take about 3,000 international units of the vitamin daily, or the amount in three standard pills. That is above Health Canada's current upper recommended limit of 2,000 IU, which Dr. Giovannucci said "may be too conservative."
There are an estimated 75,000 heart attacks each year in Canada, leading to about 22,000 deaths,
making it one of the leading causes of premature death.