Stress hormone may speed up brain aging.

For 20 years, studies of rats and other nonhuman animals have suggested that sustained exposure to high concentrations of stress hormones provokes cell loss in the hippocampus, a brain structure integral to memory and spatial navigation.

A new study indicates that cortisol, the major human stress hormone, can provoke hippocampal deterioration and cognitive declines associated with aging in healthy people.

Elderly individuals with fairly high cortisol concentrations that rose further over a 5-year period displayed substantially smaller hippocampal volume than folks of the same age who had moderate, gradually declining concentrations of cortisol in their blood over the same period, reports a team of neuroscientists headed by Sonia J. Lupien of McGill University in Verdun, Quebec.

Moreover, members of the group with higher cortisol concentrations--which nonetheless fell within the normal range--performed much worse on memory tasks that rely on a functional hippocampus. These tests consisted of memory for pictures of common items seen the day before and immediate recall of walking paths from one location to another in an experimental maze. The findings appear in the May Nature Neuroscience.

"Lupien and colleagues provide substantial evidence that long-term exposure to adrenal stress hormones may promote hippocampal aging in [healthy] elderly humans," state Nada M. Porter and Philip W. Landfield of the University of Kentucky in Lexington in an accompanying commentary.

Eleven elderly men and women between the ages of 63 and 80 participated in the investigation. Cortisol measurements were taken annually for 5 years. During home visits, the six volunteers who displayed high and rising cortisol concentrations reported more intense feelings of stress in their lives than the five people whose cortisol readings started out moderate and then declined.

After 5 years, magnetic resonance imaging scans revealed that hippocampal volume was markedly smaller in the participants with the highest cortisol measurements and the largest cortisol jumps from year to year.

By driving up concentrations of adrenal hormones in the blood, chronic stress may contribute to brain cell destruction and interfere with the generation of new hippocampal neurons in adults' brains (SN: 3/21/98, p. 180), Lupien and her coworkers propose.

The new findings complement preliminary evidence of smaller-than-average hippocampal volume among people who develop long-lasting stress reactions to traumatic events, such as military combat or childhood sexual abuse (SN: 6/3/95, p. 340).

It's unclear whether adrenal hormones directly affect the hippocampus and, if they do, how they alter cellular activity, say Porter and Landfield.