Lifestyle and stroke risk

BOSTON, MASSACHUSETTS. There is overwhelming evidence that maintaining a healthy lifestyle (not smoking, eating a healthy diet, engaging in regular, moderate exercise, and maintaining optimal body weight) can reduce the risk of cancer, diabetes, and cardiovascular disease more than any other intervention.

Researchers at the Harvard Medical School now report that a healthy lifestyle also materially reduces the risk of suffering a stroke, particularly one caused by a blood clot or the rupture of atherosclerotic plaque (ischemic stroke). The Harvard researchers describe a low-risk lifestyle as:

  • Not smoking
  • A body mass index < 25 kg/m2
  • At least 30 minutes/day of moderate physical activity
  • Modest alcohol consumption (5-30 g/day for men, 5-15 g/day for women)
  • Scoring within the top 40% of a healthy diet score

A healthy diet was defined as follows:

  • High intake of vegetables, fruits, nuts, soy and cereal fiber
  • High ratio of chicken plus fish to red meat
  • High ratio of polyunsaturated to saturated fat
  • Low intake of trans-fatty acids
  • Daily supplementation with multivitamins for 5 years or more

The Harvard lifestyle/stroke risk study is a very large one involving 43,685 men enrolled in the Health Professionals Follow-up Study (begun in 1986) and 71,243 women from the Nurses’ Health Study (begun in 1976). All participants were free of cancer and cardiovascular disease at baseline. The mean age at baseline (study entry) was 50 years for women and 54 years for men.

During follow-up, a total of 994 strokes (600 ischemic, 161 hemorrhagic [caused by a burst blood vessel], and 233 of unknown type) were documented among male participants. A total of 1559 strokes (853 ischemic, 278 hemorrhagic, and 428 of unknown type) were documented among female participants. Women with all 5 low-risk factors as defined above were found to have an 81% lower risk of suffering a stroke (79% lower risk of suffering an ischemic stroke) compared with women who had none of these low-risk factors, i.e. a highly unhealthy lifestyle. Corresponding risk reductions for men were 69% for total stroke and 80% for ischemic stroke. Unfortunately, only 2% of women and 4% of men had all 5 low-risk factors. Heavy smoking was, by far, the most significant risk factor for stroke followed by obesity (BMI over 30 kg/m2), lack of exercise, and excessive alcohol consumption.

Adherence to a healthy diet was clearly more important for women than for men with the very worst diet increasing total stroke risk by 47%, ischemic stroke risk by 33%, and hemorrhagic stroke risk by 70% among women. Corresponding figures for men were 16%, 16%, and 10%. The researchers conclude that 47% of all strokes (54% of ischemic strokes) among women can be attributed to lack of adherence to a low-risk lifestyle. Corresponding figures for men are 35% and 52%.

Chiuve, SE, et al. Primary prevention of stroke by healthy lifestyle. Circulation, Vol. 118, August 26, 2008, pp. 947-54
Gorelick, PB. Primary prevention of stroke – Impact of health lifestyle. Circulation, Vol. 118, August 26, 2008, pp. 904-06 (editorial)

Editor’s comment: It is not clear how many person-years were involved in these follow-up studies. However, assuming that follow-up was completed in 2006 (last dietary evaluation was in 2002) would result in a maximum follow-up for women (nurses) of 2.14 million (30 x 71243) person-years and 0.87 million (20 x 43685) persons-years for men (health professionals). Thus, total stroke rates would be 0.11%/year for men and 0.07% for women. These are indeed very low rates when compared to the oft-quoted rate of 1%/year among the general US population. I noticed this discrepancy in a 14-year follow-up study of the health professionals published in 2003. Following is an explanation provided by Dr. Ka He, the lead author (personal communication to me, November 30, 2003):

The annual incidence of new and recurrent stroke in the US is about 700,000 according to the American Stroke Association. Based on a population of 270,000,000 the annual rate is 0.26 per 100 person-years, or 0.26% per year. Stroke risk, of course, increases with age so it would clearly be higher if, for example, only people over 50 years of age were considered. Says Dr. He, “In our study, we only count the first event not recurrent stroke. Also, the participants are all healthcare professionals. They are health-conscious and relatively healthy (they were free from any CVD and diabetes). I would not be surprised if there is relatively low rate of stroke in our cohort.”