Coronary Heart Disease - Why are Women so Superior ?
Dateline: 06/14/98
Heart Disease in Women is a very important, unique and exciting topic. This article is a part of a series that focuses on the special problems of Heart Disease in Women. You can find the others in the archives.
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This week, the topic is ....
WHY ARE WOMEN SO SUPERIOR ?
This is one of the most fascinating questions clinical epidemiologists are asking themselves. There is a well-defined gender gap when it comes to an analysis of risks, diagnosis and treatment of coronary heart disease. This article will attempt to reconstruct the factors responsible for this gender gap, and provide some hints on preventing heart disease for both sexes.
What are the causes of the gender gap ?
"Men are from Mars, Women from Venus" - Gray JM
Traditionally, men and women have played different roles in society. These roles result in exposure to a different set of influences. These in turn act on the organ systems in different ways.
Unhealthy behaviour patterns
Men have been exposed to a higher risk of unhealthy patterns in their lifestyles. Smoking, alcohol consumption, eating a lot of red meat and less of fruits and vegetables are more commonly seen in males. These factors however are only contributory, and not causative, of coronary disease.
Work outside home
While it has been suggested that work stresses are in a large part responsible for coronary heart disease, recent studies focussed on working women draw different conclusions. For instance, the heart disease risk has been shown to be higher only in subordinate, clerical posts. Successful working women are NOT at a higher risk.
Social supports and Community style
Men and women have differing socialization needs and skills. Men have a lesser propensity to share feelings, and the resultant inner anger releases increased amounts of stress hormones that accelerate the development of atherosclerosis. Men also have fewer social supports, and are more likely to name their spouse as their favorite confidant. Social supports are cardio-protective.
Coronary prone behaviour
The prototype of a behaviour pattern that is at high risk for coronary disease is more likely seen in males. The so called "type A" personality has aggressiveness, competitiveness, hostility, time urgency and is associated with coronary heart disease in both sexes.
Does the way studies are conducted have anything to do ?
Certainly there has been a bias involved in most studies published on coronary heart disease comparisons between the sexes. For instance, exercise has been reported not to benefit women as much as men. However, these studies that are based on questionnaires focussed on sports, and ignored energy expenditure in household work. Vacuuming a two storey house is as energy intensive as playing nine holes of golf !
Are hormones responsible for this gender gap ?
Hormones might have an effect, but it is as yet unproven. Dehydro-epi androsterone (DHEA) is a masculinizing hormone. Increased levels of DHEA have been shown to protect against coronary heart disease - but only in men ! The mechanism of this is unclear.
Another is estrogen, the feminizing hormone. Pharmacologic doses of estrogen have been shown to improve exercise tolerance levels in post-menopausal women. Perhaps a sex-specific estrogen receptor in the inner lining of coronary arteries responds to estrogens. This might explain the selective benefit for women over men.
More evidence for the protective nature of estrogen comes from the observation that men universally have higher risks of coronary artery disease and that, in women who have early menopause, the female advantage is lost. The cardioprotective action of estrogen may be due to its effect on the lipid profile (reduced LDL cholesterol levels).
What then are the common risk factors for women ?
Most of the risk factors are common to both sexes. Generally, though, men have a higher exposure rate to these factors. Cigarette smoking, dietary fiber lack, vitamin C deficiency, blood viscosity, uric acid levels, low HDL cholesterol and high triglycerides are all associated with high risk in both men and women. Perhaps the only factors that decrease the risk profile in men are exercise, alcohol consumption and lower serum fibrinogen levels.
Then why is there a gender gap ?
The clue may lie in three factors that have a greater effect - that is, they contribute more to coronary heart disease - in women than men. The short list of these factors is
diabetes
low HDL cholesterol
high triglycerides
These are a part of a metabolic syndrome that exists in association with insulin lack and lipid disorders (dyslipidemia).
Diabetes
The most striking risk factor in women is diabetes mellitus. Coronary heart disease risk in women diabetics is twice as high as diabetic males. No other common risk factor so nearly erases the female advantage. The mechanism for such a difference needs further evaluation.
Cholesterol and Triglycerides
Low HDL cholesterol and high triglyceride levels also have a more significant effect on causing heart disease in women than in men, but the magnitude is not as dramatic as diabetes. For each mg/dl rise in HDL levels, the risk of coronary disease is reduced by 2% in men, but by 3% in women.
Sex linked inheritance
Intrinsic genetic factors also are responsible for the gender gap. This is evidenced by the consistent coronary artery disease sex ratio in different countries, cutting across differences in lifestyle, diet, culture and habits. The mechanisms of this has however not been explored deeply. Behaviour pattern may be influenced as early as in fetal life, when hormone differences between sexes is first manifest. Also, women are more resistant to infections than men. This might explain a delayed development of atherosclerosis, since there is a theory that proposes coronary atherosclerosis to be a sequel of inflammation.
Other mechanisms
Other mechanisms may also play a role. Homocysteine levels are decreased by folic acid intake in fruits and vegetables, and thus coronary heart disease risk is brought down. Iron has also been proposed as a coronary risk factor. Women have a greater iron loss (from menstrual bleeding) than men and so might be at lower risk.
In conclusion, there are many factors that account for the gender difference in coronary heart disease risk. Women have a superior risk profile, but as they also have a longer life expectancy, the absolute number of deaths due to coronary heart disease are equal among sexes. Modifying lifestyle can help bring all these risk factors under control and reduce coronary risk profiles for both men and women.
For a more detailed account of the topic discussed in this article you can refer to the journal paper in Circulation. 1997;95:252-264.
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