(Reuters Health) - Having close personal relationships in middle age that cause stress, problems or worries, may contribute to a decline in thinking ability in older age, according to a new study.
"Any relationship involves both positive and negative exchanges, especially those close relationships that are most likely to evoke ambivalent sentiments," said lead author Jing Liao of University College London.
"Negative aspects of close relationships refer to unpleasant social exchanges when the recipient finds the relationship ineffective, intrusive or over-controlling," Liao told Reuters Health by email.
Liao and her coauthors used data on 5,873 British civil servants who participated in a long-term study and underwent cognitive testing over a 10-year period, starting in middle age, around 1997.
The tests measured verbal memory and fluency. For one part of the test, participants were asked to recall, in writing, as many words beginning with an "s" as possible in one minute, then asked to recall as many animal names as possible for another minute.
The participants had filled out questionnaires on their social relationships in 1990 and did the same three more times after 1997.
They answered questions about how much their close relationships produced worries, problems and stress as well as how much, or how little, support they felt. To assess positive relationships, the questionnaire included items about shared interests, self-esteem and helping behaviors.
Those who reported more negative aspects of close relationships also tended to have more rapid cognitive aging, based on the periodic testing.
For people in the top-third of reported negative relationship aspects, compared to those in the bottom third, the extra decline was equivalent to an added year of aging, the researchers found.
"These differences in cognitive decline, though small, could be traced back to risk factors in midlife," Liao said. "Given (that) the incidence of dementia increases exponentially with advancing age and no effective medicine is currently available, our study provides evidence of what risk factors could be targeted before cognitive changes are irreversible."
People who reported the most negative aspects of close relationships were also more likely to have symptoms of depression and diabetes than others, according to the results published in the American Journal of Epidemiology.
There is evidence that, in general, those with a partner or those who are less socially isolated report better quality of life and live longer, Liao said.
But healthy people are more likely to have a partner and be more socially engaged, she noted.
"Previous studies, including some of those I have conducted with my colleagues on the Midlife in the United States (MIDUS) study, have found that close relationships that involve strain and conflict are associated with poorer executive functioning," said Margie E. Lachman, director of the Lifespan Initiative on Healthy Aging and Lifespan Lab at Brandeis University in Waltham, Massachusetts.
"This study, which followed the same people over time, was able to confirm that experiencing social strain and stress in close relationships has an impact on cognitive declines," Lachman, who was not part of the new study, told Reuters Health by email.
Negative aspects of relationships appear to result in cognitive declines, rather than the other way around, she said.
"Further work is needed, however, to see to what extent declines in cognitive functioning might lead to increases in actual negative interactions in close relationships, rather than just describing the relationship as characterized by lack of support and causing stress," Lachman said.
The British civil servants in the study were likely better supported and experienced less cognitive decline than the general population, so the association Liao's group found may be even stronger for other groups, Liao noted.
The elderly should be encouraged to foster protective relationships, she added.
"Interventions should be targeted at how to reduce negative interactions and alleviate adverse psychological reactions," potentially by minimizing or resolving conflicts and enhancing the ability to cope, Liao said.