Researchers found people with one copy of a commonly mutated gene had doubled the risk of dying from a heart attack or stroke.
The gene is involved in a disease known as hemochromatosis, which allows too much iron to be absorbed from food.
Earlier studies had identified the gene, and doctors knew that people who inherited one copy of the mutated gene from each parent had a much higher risk of heart disease, as well as liver damage and liver cancer.
Writing in the journal Circulation, published by the American Heart Association, two separate groups said they found that people with just one copy of the hemochromatosis gene also had a higher risk.
One in 3,000 people is diagnosed with the condition in the United States. About one in 250 Americans has two copies of the mutated gene and one in 10 has one copy.
While most people store between two and four grams of iron, those with hemochromatosis may accumulate 20 grams or more in their blood's hemoglobin.
There are no real symptoms, but some patients may see their skin turn a rusty orange color from the extra iron in their blood and organs are damaged by the accumulated iron.
Mark Roest and colleagues at Utrecht University Medical School in the Netherlands studied 12,239 middle-aged women. Those who had just one copy of the hemochromatosis gene had double the risk of dying from a heart attack or stroke.
Women who smoked, had high blood pressure and were carriers of the mutated gene had nearly 19 times the risk of heart attack and stroke death compared to non-smokers with normal blood pressure who did not have the mutation, Roest reported.
"This is the first large study to find a significant association between women who are carriers of the gene and cardiovascular disease," Roest said in a statement.
He said the study also supported the idea that women are protected
from heart disease before menopause because they lose iron every month during menstruation.
In a second study in Circulation, the researchers checked for the hemochromatosis gene among 1,150 Finnish men. "Carriers of the gene have more than twice the risk for a heart attack compared to non-carriers," they wrote.
Dr. Jukka Salonen and colleagues at the University of Kuopio in Finland had earlier found that regularly giving blood reduced the risk of heart disease.
"Based on what we know now, a strong case could be made for recommending blood donation as a way to lower iron levels, thus lowering heart attack risk," Dr. Jerome Sullivan of the University of Florida in Gainesville said in a commentary.
Red meat is rich in iron and Americans were once urged to eat plenty to get enough iron. Many cereals are fortified with 100-percent of your daily iron breads and other processed foods are also iron-fortified.
But the aerage diet now provides a more than adequate iron intake, and red meat is also high in saturated fat, which is a major cause of heart disease.
Dr. Warren Furey of Northwestern Memorial Hospital in Chicago, who was not involved in either study, suggests that both men and women watch their iron intake.
"I'd be very cautious of having things with iron if you're past the menstrual childbearing age groups, and for men, I don't know of any real benefit for iron unless someone has told you you're
iron-deficient," he said.