Benefits for overweight women with heart disease
A Norwegian study has found that overweight women with cardiovascular disease are less at risk of serious consequences from their illness than normal weight women with the same disease. The opposite is true for men.
It’s a paradox: Plenty of research shows that being overweight or obese increases the risk of cardiovascular disease, such as constricted arteries, angina and coronary thrombosis.
But if you first have a heart disease and then gain weight, the situation completely changes.
A number of studies show that overweight and even slightly obese people with cardiovascular disease actually are at less risk of dying from their heart problems than similar patients with normal weights.
The phenomenon is called the “obesity paradox” and it appears to apply to heart disease and a few other chronic illnesses.
But the correlation between weight and heart disease is complicated by mixed results. While some studies have shown a bit of surplus body fat to be advantageous, other studies conclude that it is a disadvantage, or that it makes no difference.
A team of researchers from Vestfold Hospital, Haukeland University Hospital, the University of Oslo and the University of Bergen have come closer to a possible explanation for these research result disparities.
The key, it seems is a difference between men and women.
Elevated risk for men
The researchers followed the outcomes for 4,000 patients with angina or suspected heart disease. The participants were split into groups by gender and weight: Normal-weight people with BMIs of 18.5 to 25, overweight individuals with BMIs from 25 to 30 and obese people with BMIs above 30.
How did gender and weight affect the development of the disease?
Among the men, being a bit overweight did not have much significance.
But men with heart disease who were obese (BMI of 30+) ran an 80 percent higher risk or heart attacks and a 60 percent higher risk of fatal heart disease than men with similar afflictions who weighed less.
The exact opposite was true for women.
Obesity did not seem to affect them. And being overweight actually seemed to have a protective effect. Overweight women with cardiovascular disease had nearly a 50 percent lower risk of infarcts than women in the normal weight range with the same disease.
Remarkably, these differences among men and women have been relatively unknown.
“Only a few previous studies have made such a division between men and women,” explains the main author of the study, Heidi Borgeraas of the Morbid Obesity Center at Vestfold Hospital in Norway.
Professor Jøran Hjelmesæth at the Morbid Obesity Center contributed to the study and thinks gender can be a much bigger factor in medical issues than previously anticipated.
“I believe we scientists have been lax in thinking about gender differences. Fortunately, this has attracted a lot more attention in recent years,” he says.
The consequences of this new discovery remain unclear. The cause of the obesity paradox and the big differences in how fatness affects men and women are still quite obscure.
On the one hand, it is possible that women’s fat actually protects them directly from the disease. But another explanation is that normal weight women who develop cardiovascular disease are more seriously ill to start with.
Obesity increases the risk of heart disease
Hjelmesæth explains that an array of factors is involved when a person develops a cardiovascular disease.
“Some of the most important risk factors are genetics, advanced age, being a male, smoking and amounts of blood fats. But obesity on its own also raises the risk of heart disease,” he said.
“Slender young people who contract heart disease are probably more disposed to serious illness than people who have to get fat before they develop heart maladies," he added.
This might explain part of the obesity paradox. In this case, it might not be the fat itself that is protective, but rather that overweight people most often have a milder disorder and thus enjoy lower risks of heart attacks and death from a cardiac arrest.
It is also possible that overweight heart patients are diagnosed and treated at an earlier stage because we know that being overweight or obese is a risk factor for heart problems, explains Borgeraas.
But we cannot rule out that body fat really does have a salutary effect on cardiovascular disease among women.
A possible benefit during menopause
“The fat on overweight women often collects around the thighs and buttocks. This fat has a tendency to stay put. It is stored fat which is less biologically active,” says Hjelmesæth.
He wonders whether this kind of fat can have a positive effect, especially among menopausal women.
“When women reach menopause their bodies produce less oestrogen. They start to resemble men more with regard to developing a paunch. But the female fat they have around the buttocks and thighs can have a protective effect regarding cardiovascular diseases,” he said.
When men gain weight, they often carry it around their waists, which is something we know has negative effects on health.
But to date medical science has no adequate explanation for why female heart patients who are overweight run a lower risk of death from the disease than patients who are slimmer, warns Hjelmesæth.
“It’s an advantage for the general population to have a normal weight. We cannot say whether it would be an advantage for female heart disease patients to put on some extra kilos intentionally,” he said. “On the other hand, it now seems hard to advise overweight women with heart disease to go on a diet to slim down – as has been the routine earlier.”
Hjelmesæth says there is a little good news in the finding. “We can tell overweight women with suspected cardiovascular disease that they at least do not have poorer prognoses than women in their situation with normal weights.”
Read the Norwegian version of this article at forskning.no
Translated by: Glenn Ostling
- Association of body mass index with risk of acute myocardial infarction and Mortality in Norwegian male and female patiants with suspected stable angina pectoria: a prospective cohort study, BMC Cardiovascular Disorders, 2014, 14, 68.