has shown that long-term, chronic stress can suppress the immune system. This short-term enhancement is stronger during winter than during summer. Staci Bilbo, a doctoral student in psychology at The Johns Hopkins University, was the other lead author on the study. Bilbo is currently working in the lab of Randy Nelson, another co-author and professor of psychology and neuroscience at Ohio State.

The study involved 50 Siberian hamsters. Using artificial light, the researchers exposed half of them to long days (15 hours of light per day) to simulate summer conditions. The other half lived in short days (9 hours of light per day) to simulate winter conditions.

After 10 weeks of living under these conditions, some hamsters were tested for levels of key immune cells in their bloodstream, including leukocytes, lymphocytes, T cells and NK cells.

The results showed that hamsters living in winter-like conditions have higher baseline levels of these immune cells than do hamsters living in summer-like daylight conditions.

"It is more difficult for hamsters to survive in the winter because of stressors like cold and reduced availability of food," Bilbo said. "We found that the animals seem to use the length of day to warn of the onset of these stressors and then to enhance their immune system when winter approaches."

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Contact: Firdaus Dhabhar
Dhabhar.1@osu.edu
614-688-8562
Ohio State University
18-Mar-2002

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