The study of over 6,700 people aged between 45 and 84 years, reported in the American Heart Association's journal Stroke, compared the rates of full and mini-stroke between people of different psychological profiles rated via questionnaire.
Compared with people who had healthy psychological scores, those with the poorest scores showed the following percentage increases in their likelihood of suffering a stroke or transient ischemic attack (TIA):
- 86% for a high score on depressive symptoms
- 59% for the highest ratings of chronic stress.
On the effect of feelings of hostility - "which is a negative way of viewing the world" and was assessed by the person's "cynical expectations of other people's motives" - this resulted in a doubling of the risk versus people who did not score highly on this profile. Feelings of anger, however, had no effect.
Dr. Susan Everson-Rose, lead author and associate professor of medicine at the University of Minnesota in Minneapolis, says:
"There's such a focus on traditional risk factors - cholesterol levels, blood pressure, smoking and so forth - and those are all very important, but studies like this one show that psychological characteristics are equally important."
The chronic stress was measured using ratings for five different domains of the participants' lives:
- Personal health problems
- Health problems of people close to them
- Job or ability to work
Decade-long study covered six American cities
The data for this analysis came from a study across six US sites known as the Multi-Ethnic Study of Atherosclerosis.
The 6,749 participants were from a mix of ethnic backgrounds across Baltimore, MD, Chicago, IL, Forsyth County, NC, Los Angeles, CA, New York City, NY, and Saint Paul, MN.
The almost equal numbers of men and women showed no evidence of cardiovascular disease at the start of the research in the early 2000s.
During the first 2 years of the recruitment, the baseline ratings of depression and chronic stress were assessed, and the subjects were monitored for an additional 8.5 to 11 years.
During the study, 147 strokes and 48 TIAs occurred, and the researchers did a statistical analysis at the end to compare the rates of disease between different levels of psychological health.
Possible biological mechanisms
The authors say they have excluded the possibility that the stroke results could be explained by poor psychological health tending to have a bad effect on physical lifestyle (people experiencing "stress and negative emotions typically have more adverse behavioral risk profiles, and experience difficulty in maintaining healthy lifestyles and adhering to treatment recommendations").
"Better understanding of important, potentially modifiable stroke risk factors, including stress and negative emotions, is needed given the aging population and increasing burden of stroke," say the researchers.
The lifestyle factors taken into account were:
- Physical activity
- Alcohol consumption
- Body mass index
- Blood pressure.
Independent of these factors, if depression and stress can be assumed to have a direct causal effect on stroke, then, the authors offer only theoretical ideas about what the biological link might be.
"Stress and negative emotions activate the hypothalamic-pituitary-adrenal axis," they write, and this activation of the brain's stress center influences blood clotting, among a number of other effects listed in the paper.
But these factors were not tested in the study. Another pathway that was tested, that of inflammatory effects, was tested to some extent, but "little evidence" was shown for it.
Inflammatory pathways are "plausible" because "the psychosocial factors measured here are associated with increased C-reactive protein, fibrinogen, and interleukin 6, which are related to stroke risk."
The study's conclusion reads: "Our study demonstrates associations between excess stroke/TIA risk and depressive symptoms, chronic stress, and hostility, which were not explained by traditional stroke risk factors, inflammatory markers, or subclinical atherosclerosis.
"Better understanding of important, potentially modifiable stroke risk factors, including stress and negative emotions, is needed given the aging population and increasing burden of stroke."