According to a recent study, stress can impair memory and can even reduce brain size in the middle age.

Adults in their 40s and 50s with higher levels of cortisol - a hormone linked to stress - performed worse on memory and other cognitive tasks than peers of the same age with average cortisol levels, the research found.

Higher cortisol in the blood also was associated with smaller brain volumes, according to the study.

The findings have been published in Neurology, the medical journal of the American Academy of Neurology.

"In our quest to understand cognitive ageing, one of the factors attracting significant interest and concern is the increasing stress of modern life," said study senior author Sudha Seshadri. "One of the things we know in animals is that stress can lead to cognitive decline. In this study, higher morning cortisol levels in a large sample of people were associated with worse brain structure and cognition."

Lead author Justin B. Echouffo-Tcheugui of Harvard Medical School said, "Cortisol affects many different functions, so it is important to fully investigate how high levels of the hormone may affect the brain."

"While other studies have examined cortisol and memory, we believe our large, community-based study is the first to explore, in middle-aged people, fasting blood cortisol levels and brain volume, as well as memory and thinking skills," added the lead author.

Memory loss and brain shrinkage were found in the study's middle-age participants before the onset of any symptoms, Dr Echouffo-Tcheugui noted. He said it is important for physicians to counsel people with higher cortisol levels on ways to reduce stress, such as getting enough sleep and engaging in moderate exercise.

"The faster pace of life today probably means more stress, and when we are stressed, cortisol levels increase because that is our fight-or-flight response," Dr Seshadri said. "When we are afraid, when we are threatened in any way, our cortisol levels go up. This study adds to the prevailing wisdom that it's never too early to be mindful of reducing stress."