Women who experience a lot of stress in middle age are at increased risk of developing Alzheimer’s disease and other forms of dementia late in life, according to a new report. The findings come from a study of 800 women living in Sweden who were followed for nearly four decades. Though the study did not look at men, the results suggest that stress may have longstanding detrimental effects on the brain for all of us.

For the study, researchers examined the long-term medical and cognitive health of 800 women who were part of the large and ongoing Prospective Population Study of Women in Gothenburg, Sweden. The women started the study in 1968, when most were in their 40s or 50s.

Over the next 38 years, the women were given regular health assessments every 5 to 10 years, including looking for signs of the memory loss of Alzheimer’s and other types of dementia.

At the beginning of the study, the women were asked whether they had experienced major stresses like divorce, the death of a spouse or child, or serious illness in a close family member. Other sources of stress they were asked about included unemployment, either  themselves or a spouse, lack of social support, or a history of abuse.

At each follow-up visit, the women were also asked whether they had experienced symptoms of stress lasting at least a month. Such symptoms included irritability, feeling tense or fearful, nervousness, anxiety or sleeping poorly. The more stressful events they had experienced in the past, the more likely they were to experience symptoms of distress.

At the start of the study, about 25 percent of the women had experienced one major life stressful event, 23 percent had experienced at least two, 20 percent had experienced at least three, and 16 percent had experienced four or more. The most common major stressor was mental illness in a close family member.

During the follow-up period, over the next four decades, around one in five of the women had developed dementia, most often Alzheimer’s, at an average age of 78. Those who reported experiencing the most stressful events in middle age were at 21 percent increased risk of developing Alzheimer’s in old age, and at 15 percent higher risk of developing other forms of dementia.

The authors note that more study is needed to confirm the results. They also do not know whether psychological counseling and other stress management techniques might mitigate the detrimental long-term effects of stress on the brain.

But they also note that stress can affect the central nervous system and immune system, and that levels of stress hormones may remain high for many years after a traumatic event. Other studies have shown that stress can damage brain cells and promote inflammation, which has been increasingly linked to Alzheimer’s disease. Stress has also been linked to high blood pressure, which can also be bad for the brain.

Many factors can contribute to Alzheimer’s, including age and genetics. Long-term stress may be one more factor that may play a role in the onset of dementia.

By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by William J. Netzer, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.

Source: Lena Johnasson, Xinxin Guo, Tore Hallstrom, et al: “Common psychosocial stressors in middle-aged women related to longstanding distress and increased risk of Alzheimer’s disease: a 38-year longitudinal population study.” BMJ Open 2013, September 30.