LONDON – Major lifetime stressful experiences are associated with cognitive decline in later life, with each stressful event linked to a detrimental effect on executive function similar to between 1 and 4 years of ageing, a new study suggests.
The study was presented here at the Alzheimer’s Association International Conference (AAIC) 2017.
“Our take-home message is that social environment is very important for future cognitive health,” said Megan Zuelsdorff, PhD, University of Wisconsin School of Medicine and Public Health, Madison, during her presentation.
“This may sound like bad news, but actually, some of these effects may be modifiable,” Dr Zuelsdorff said. “While we may not be able to prevent these life events, we may be able to minimize their impact on cognition. We need to look at what sort of social and financial support these people had and whether this made a difference and what coping strategies helped, so we can try to translate these academic data into public policy.”
Commenting for Medscape Medical News, Keith Fargo, director of scientific programs at the Alzheimer’s Association, said the study highlights the lifelong component of risk for Alzheimer’s and cognitive decline.
“We think of cognitive decline and Alzheimer’s as problems of ageing, but we’re seeing now more and more that factors earlier in life have an impact on cognitive health later in life,” he said. “We know that blood pressure, diabetes, and obesity in midlife make a difference, and now were seeing that risk factors may go all the way back to childhood.”
He added: “While we might not be able to control these stressful life events, we can control other factors, such as smoking, exercise, and healthy eating, to try to lessen the effect of lifetime stressors.”
Worse in African Americans
The study also showed that the cognitive detriment associated with stressful life events was greater for African Americans.
“We found that lifetime stress is a stronger predictor of executive function than genetic risk, age, and years of education for African American participants, and is a major contributor to racial disparities in cognitive health,” Dr Zuelsdorff noted.
Commenting on this particular finding, Mary Sano, PhD, Alzheimer’s Association Medical and Scientific Advisory Council, said: “We already know that African Americans have a greater risk of cognitive decline and dementia, and this study shows they also appear to be more susceptible to the effects of life stress on cognition – so they have a ‘double whammy’ to deal with.”
The study, which was part of the Wisconsin Registry for Alzheimer’s Prevention, included a total of 1314 adults (1232 non-Hispanic white and 82 African American) who were healthy at baseline. The data were enriched for a parental history of Alzheimer’s.
The study had a longitudinal design. The participants, who were assessed through visits and cognitive testing every 2 years, were asked about 27 lifetime stressful experiences. Examples of these stressful events included the following: parent(s) who drank so much it caused problems; divorce; divorce of parents; death of a child or sibling; having a child with a severe illness; bankruptcy; being fired from a job; experiencing combat (ie, being deployed to a war zone in the armed forces); physical or sexual assault; and dropping out of school.
The researchers measured six domains of cognitive function encompassing both executive function and memory. Results showed that lifetime stressful events had the most effect on speed and flexibility – a key domain of executive function.
After controlling for other factors, in the whole cohort there was a highly significant association between the number of life stress events and speed and flexibility, with each additional stress events linked to a detriment in this score of 9% of one standard deviation (a beta-coefficient of -0.09; P = .001).
Dr Zuelsdorff said that in terms of brain ageing, this was equivalent to a decline of 1.5 years.
The effect was greater in the black population, with each life stressor associated with a decline of 16% of one standard deviation in the speed and flexibility score (a beta-coefficient of -0.16; P = .002). Dr Zuelsdorff said this was equivalent to 4 years of brain ageing.
Life stress events were also associated with a reduction in working memory in African Americans, with each life stress event linked to a decline of 11% of one standard deviation (beta coefficient of -0.11; P = .01).
There was no effect of stressful life events on working memory in the white population.
Dr Zuelsdorff reported that African Americans experienced more stressful life events (mean, 4.5 events) than whites (mean, 2.8 events). “There were several African Americans who reported 12 or 13 of the 27 stressful life events, and incredibly, one individual had 17 of these life events,” she noted.
The African American and white cohorts were similar in other key ways: age (mean, 58.5 years), proportion of APOE e4 risk allele carriers (38.5%), years of education (mean, 16.2 years).
But the African Americans had higher body mass index, were more likely to be current smokers, had less reported physical activity, and had received a lower quality of education. These factors were controlled for in the analysis.
Dr Zuelsdorff added that future studies need to explore differential cognitive vulnerability to stress: “We need to focus on the role for biological stress processes in brain aging and the importance of timing and duration of life experiences,” she said.
The study was funded by grants from the National Institutes of Health. Dr Zuelsdorff has disclosed no relevant financial relationships.
Alzheimer’s Association International Conference (AAIC) 2017. Abstract 14332, presented July 16, 2017.