sex, age, genetics and culture
By CAROLYN ABRAHAM
Globe and Mail: Monday, August 30, 2004 -
A landmark Canadian-led study has found that
the causes of heart disease are the same in all people, regardless of age,
sex, colour, culture or where they live.
The unexpected conclusion, based on research
involving nearly 30,000 people in 52 countries, upends the view that gender,
genetics, or ethnicity plays a major role in determining who suffers a heart
Even project leader Salim Yusuf, who has devoted
much of his career to links between disease and ethnicity, was surprised to
learn that it is largely nurture, not nature, that predicts who will fall prey
to the world's No. 1 killer.
"I expected to find differences in risk factors
based on ethnicities, which we did not find. But I also never expected that
we'd be able to explain 90 per cent of the global risk of heart disease," said
Dr. Yusuf, director of the Population Health Research Institute at McMaster
University and Hamilton Health Sciences centre.
The research team, which included colleagues from
262 centres on every inhabited continent, concluded that high levels of bad
cholesterol and smoking were by far the strongest predictors, accounting for
two-thirds of the world's heart attacks.
These were followed by high blood pressure,
diabetes, abdominal obesity, stress, a lack of daily fruits and vegetables and
a lack of exercise.
Together, these nine risk factors, all of which
hold the alluring promise of being changed or modified, accounted for 90 per
cent of heart-disease cases worldwide.
The finding "provides overwhelming proof to
debunk" the so-called 50-per-cent myth, which suggests half the causes of
heart disease are unknown because half the people who get it have no obvious
risk factors, said study contributor Sonia Anand, a clinician and associate
professor of medicine at McMaster.
The data also explode other myths and reveal
remarkable trends in the incidence of heart disease. Among them: Consuming
more than three alcoholic drinks a week can moderately protect women from
heart disease, a phenomenon other studies have already confirmed in men. Women
tend to have their first heart attacks 10 years later than men. Having a
paunch, or potbelly, is riskier than just being overweight.
For non-smokers with good cholesterol levels,
stress is the most powerful predictor of a heart attack.
Men in the Middle East and South Asia suffer
first heart attacks 10 years younger than men in Western Europe or China,
perhaps due to better prevention strategies in the West.
Cholesterol contributes to more than 74 per cent
of heart attacks in Africa.
Fully explaining these trends demands further
study, and researchers have yet to take into account socioeconomic risk
But Dr. Yusuf said the most exciting prospect at
the moment is that "this information tells us how to prioritize public-health
campaigns by region," since some risk factors are more common in certain
In China, for example, smoking is the major
culprit, contributing to more than a third of heart attacks. But obesity in
China is remarkably low, accounting for less than 6 per cent of cases.
In Western countries, including Canada, where
smoking rates are declining, countering abdominal obesity should be the
priority since it explains roughly 60 per cent of heart attacks.
"We cannot prevent people from dying, but we can
prevent them from dying early," Dr. Yusuf said in an interview from Munich,
where he presented his pivotal Interheart study yesterday to the European
Society of Cardiology.
Alan Bernstein, president of the Canadian
Institutes of Health Research, which backed the project, along with the
Ontario Heart and Stroke Foundation, praised the ambitious study for its
international significance and its importance for Canada as a multicultural
"This isn't saying there aren't genetic
contributions to heart disease," Dr. Bernstein said.
"But with this, a doctor can look at nine
factors, with some very easy-to-test measures, way before a patient has a
heart attack, and can say, 'You are going to have a heart attack.' "
Worldwide, heart disease kills 17 million more
people than all cancers combined. But while prevention strategies are
shrinking heart-disease rates in high-income countries, numbers in the
developing world have skyrocketed.
In part, this is because deaths due to infection,
with the exception of HIV-AIDS, have plummeted in lower-income countries. As
citizens of the developing world live longer and become more Westernized, Dr.
Anand said, heart disease is expected to be the leading killer by 2020.
For this reason, researchers felt the causes of
heart disease had to be examined on a global basis. There was a feeling, Dr.
Anand said, that most other studies had focused largely on white, middle-aged
men in Western countries.
"So people thought maybe the causes are different
in women, or in young people or in people from India or China," said Dr.
Anand. "But now we see they're not." In fact, researchers discovered that a
family history of heart disease increased the ability to predict heart disease
by only 1 per cent. By comparison, lifestyle factors predict roughly
two-thirds of cases.
This, Dr. Yusuf said, "means we should be able to
prevent the majority of premature heart attacks in the world."