The finding supports the idea that -- while chronic stress seems to suppress immune function -- acute stress may enhance it.
"We're suggesting that the effect of stress could all be in the timing," said lead author Kate Edwards of the University of Birmingham in England. "What we think is that the acute stress is activating the immune system; it's preparing it for a challenge."
The authors add that the evidence remains preliminary, since the women's enhanced response only appeared with one of three flu strains and there was no evidence of the effect in men. The study appears in the March issue of Brain, Behavior, and Immunity.
To conduct the study, the authors recruited 60 healthy male and female university students. Each participant was randomly assigned to participate in one of three activities for 45 minutes: riding a stationary bicycle, competing in a mental arithmetic contest or reading quietly. Afterward, each person received a flu shot donated by GlaxoSmithKline, U.K.
When antibody levels were measured four weeks and again 20 weeks later, women in the physical and mental stress groups had more antibodies to the A/Panama flu strain than women in the control group. The exact mechanism of the immunological boost remains unclear, say the authors.
Future studies are needed to measure how acute stress may enhance immune response "using stress tasks of different natures, durations and timings in a variety of populations," the authors write.
A priority is searching for similar results among the elderly, who are most at risk of serious complications from influenza infection, Edwards said.
"We'd really like to see this confirmed in a larger-scale study and hopefully confirmed for other types of virus as well, or indeed other diseases," said Mike Gleeson of Loughborough University in England. Gleeson is also vice president of the International Society for Exercise and Immunology.
If the findings hold up, he added, "you might recommend that the individual going along for a vaccination maybe walk to the hospital or clinic...so they get a bit of exercise on the way."
By Laura Kennedy, Contributing Writer
Health Behavior News Service
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Edwards KM, et al. Acute stress exposure to influenza vaccination enhances antibody response in women. Brain, Behavior, and Immunity 20(2), 2006.