TUESDAY, Oct. 1 (HealthDay News) -- Women who deal with a lot of day-to-day stressors in middle-age may have a somewhat higher risk of developing Alzheimer's later in life, a new study suggests.

The findings, published online Sept. 30 in BMJ Open, do not prove that your job or your family are raising your dementia risk. But experts said they add to evidence that chronic stress may contribute to the development of Alzheimer's disease in some people.

No one is sure why, but there are theories, according to Robert Wilson, a professor of neurological sciences and psychology at Rush University Medical Center, in Chicago.

It's possible that chronic stress, via effects on certain hormones, may reduce the efficiency of people's "brain circuitry," explained Wilson, who was not involved in the new study. And that could leave some people more vulnerable to the impact of Alzheimer's-related brain changes later in life.

But past studies have generally focused on the possible effects of stress from more-severe traumas. The new study looked at "common" stressors, said lead researcher Lena Johansson, of the Sahlgrenska Academy at Gothenburg University, in Sweden.

Her team studied data from 800 Swedish women who were followed for nearly four decades, starting when they were in their late 30s to early 50s. The women underwent periodic psychiatric exams and answered questions about everyday stressors -- such as divorce, job strain and family members' health issues.

Over 37 years, 19 percent of the women developed dementia -- most often Alzheimer's disease. And the risk climbed in tandem with the number of life stressors that the women had reported four decades earlier. For each stressor, the risk of Alzheimer's crept up 17 percent.

That doesn't prove that a stressful life is to blame, said Dr. Marc Gordon, chief of neurology at Zucker Hillside Hospital in Glen Oaks, N.Y.

But, he noted, the researchers did account for a number of other explanations for the link -- including whether the women had high blood pressure or diabetes, were overweight or had low incomes.

Other studies have tied heart disease risk factors, such as high blood pressure, to Alzheimer's, and lower income and education levels have also been linked to the disease.

Still, Johansson's team found, stressors themselves were connected to an increased risk of Alzheimer's.

Gordon, who was not involved in the study, agreed that it's "biologically plausible" that chronic stress could contribute to dementia. But a big unanswered question is whether any efforts to reduce stress in your life can also trim the risk of Alzheimer's later on.

"This type of study can't tell us if there's an intervention that can affect people's outcomes," Gordon said. "We can't make any recommendations based on this alone."

An interesting finding, Rush University's Wilson said, was that the number of stressors in a woman's life seemed to matter, regardless of whether she felt "stressed out" by them.

Women in the study were asked about their typical "distress" levels -- including tension, fear or sleep problems related to work, family or their health. Women with "longstanding" distress were at increased risk of Alzheimer's. But so were women with a greater number of life stressors.

That suggests that stressors can take a toll, even if you do not feel overwhelmed, according to study author Johansson.

"These are the kinds of stressors that grate on people day to day," Wilson noted. And this study, he said, suggests that these issues should not "just be brushed off." He agreed, though, that the question remains: Could stress reduction make a difference in people's Alzheimer's risk?

Zucker Hillside's Gordon said more studies are also needed to confirm these results in other groups of people, since this focused on white women. And even if common types of stress are linked to Alzheimer's risk, any effect on an individual could be small.

No one is sure what causes Alzheimer's, but Gordon said it's thought to be a mix of genetic factors, family history and environmental influences.

"This would be only one of many potential factors," Gordon noted.

More information

The Alzheimer's Association has more on Alzheimer's disease risk factors.