Stress during midlife has a direct correlation to the risk of developing dementia later in life in women, according to the findings of a new study.

In a study published in the most recent issue of the journal BMJ Open, a team of researchers with the Prospective Population Study of Women in Gothenburg, Sweden, spent nearly four decades following a group of approximately 800 women throughout much of their adult lives. All of the women who participated in the study were born in either 1914, 1918, 1922 or 1930, and they agreed to undergo neuropsychiatric tests at scheduled intervals.

“Our study shows that common psychosocial stressors may have severe and longstanding physiological and psychological consequences,” the study’s co-authors, led by neuropsychiatric epidemiologist Dr. Lena Johansson, said. “Stress may cause a number of physiological reactions in the central nervous, endocrine, immune and cardiovascular systems.”

The women were all tested for the first time in 1968, and then five additional times in the 37-year period following that. The results of the study showed that women who had stressful experiences during middle age -- including divorce, losing a spouse, having a child who suffered or died from a serious illness, having a family member who suffered from mental illness or substance abuse, unemployment or poor social support -- all contributed to an overall elevated risk in developing dementia.

Of the 800 participants, 425 died before the study’s completion, and 153 (19 percent) developed dementia and 104 developed Alzheimer’s disease. According to Medical News Today, on average the women began to show symptoms of dementia at age 79. Researchers said that it developed over an average period of 29 years.

Most significantly, the findings revealed that more stressful life events resulted in a heightened risk of developing dementia, with those who initially reported stressors in their midlife having a 21 percent higher chance of developing Alzheimer’s disease and a 15 percent higher chance of developing any type of dementia.

The authors believe that stress hormones are responsible, as they can lead to changes in blood sugar control and blood pressure, and result in negative effects in the brain.

Simon Ridley, head of research at Britain’s Alzheimer’s Research, said the results were not conclusive in determining whether stress caused the dementia, or if it was simply another symptom of a shared underlying cause. "From this study it is hard to know whether stress contributes directly to the development of dementia, whether it is purely an indicator of another underlying risk factor in this population of women, or whether the link is due to an entirely different factor,” Ridley said.

"We know that the risk factors for dementia are complex and our age, genetics and environment may all play a role," he told the BBC. "Current evidence suggests the best ways to reduce the risk of dementia are to eat a balanced diet, take regular exercise, not smoke, and keep blood pressure and cholesterol in check. If you are feeling stressed or concerned about your health in general, we would recommend you talk this through with your GP."