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People with high blood levels of cortisol , the “stress hormone,” may have poorer memory and thinking skills than those with lower levels.

Cortisol is produced by the adrenal glands and is involved in regulating blood sugar levels, reducing inflammation, controlling salt and water balance and other body functions.

Researchers gave tests for memory, abstract reasoning, visual perception and attention to 2,231 people, average age 49 and free of dementia. They recorded blood levels of cortisol and did M.R.I. examinations to assess brain volume.

The study, in Neurology, controlled for age, sex, education, body mass index, blood pressure and many other variables, and found that compared with people with average levels of cortisol, those with the highest levels had lower scores on the cognitive tests. In women, but not in men, higher cortisol was also associated with reduced brain volume. There was no association of the lowest cortisol levels with either cognitive test scores or brain size.