It’s never easy to isolate the causes of any disease. An individual who smokes and then suffers a stroke did not necessarily suffer stroke because of smoking; it may have been because he or she ate too much fat or didn’t exercise or had too high blood pressure. Or it may have been a combination of all of those factors or none of them. Human diet, health and behaviour is sometimes too complicated to nail down any one risk factor as greater or lesser than others.
But two Finnish studies, involving 16,649 men and women between the ages of 30 and 59, set out to evaluate the causes of stroke by rigourously analyzing all known major risk factors, separately and jointly.
The Finns looked at smoking, cholesterol levels, individual blood pressure, rates of hypertension, exposure to drug therapy for hypertension, and body mass index, or obesity. They looked especially hard at glucose tolerance, monitoring both those men and women who were already diabetic when the study began, and those who developed diabetes as the studies progressed over 15 and 20 years.
What they found was more or less as expected. Smoking, hypertension, obesity and high cholesterol all increase the risk of stroke in men, and all but cholesterol were shown to have the same effect on women. Most factors had a markedly greater effect on women. For example, though far more men in the survey smoked than women, women who did smoke ran a risk of fatal stroke 1.8 times greater than women who did not. For men, the comparable figure was under 1.4 (though it was higher among non-diabetics).
An even clearer indicator was drug treatment for hypertension. Men who had taken antihypertensive drugs were twice as likely to die of stroke as men who had not. Among women, again, the disparity was even greater. These figures reflect the fact that patients who need antihypertensive drugs are obviously more likely to be hypertensive. It is the hypertension that contributes to stroke, not the drug that combats hypertension. And of course, when drug therapy succeeds in controlling hypertension, the risk of stroke is reduced.
Of all the indicators of stroke, by far the strongest proved to be diabetes. Other things being equal, men with diabetes were 3.8 times more likely and women six times more likely to die of stroke than non-diabetics of the same sex and age. Put another way, twice as many of the men who died from stroke were diabetics as of the men who remained alive at the end of the follow-up. Among women who died of stroke, the proportion of diabetics was three times as high as among women who died of other causes and eight times as high as among women who survived to the end of the survey.
The risk of stroke from diabetes was also shown to grow with time. Men who had diabetes when the survey began were four times more likely to die of a stroke than men who developed diabetes during the course of the survey. In fact, late-developing diabetics were only 1.7 times more at risk of stroke than the non-diabetics. That’s a lower risk factor than non-diabetic smokers faced.
Women who had diabetes at the start of the survey were at more than twice the risk of a fatal stroke than those whose diabetes was diagnosed later on. All of this seems to show that it takes time for diabetes to really raise the risk of stroke significantly.
Finally, although women are more susceptible to the effects of most stroke risk factors, they should not feel especially at risk. No women need fear one risk factor this survey only touched upon: the risk of being a man. More men than women died of stroke in the survey although women outnumbered men. Men, in fact, are twice as likely as women to suffer a fatal stroke.
One should remember when reading these results that women in the various risk categories were compared only with other women. Insofar as it looks at gender, what this survey really tells us is that smoking, obesity and, above all, diabetes have much more impact on women than men in terms of stroke risk. While fewer women die of stroke than men, more female fatal strokes (one-third of the total) can be attributed directly to diabetes, double the rate for men.