Why Bird Viruses and Human Viruses Increase in Winter
Copyright 2005, James Michael Howard, Fayetteville, Arkansas, U.S.A.
Testosterone is an immunosuppressant. Testosterone reduces both
cell-mediated and humoral immunity in birds (Behvioral Ecology 2000; 11:
654-662). In the "Northern pintail duck," testosterone is lowest from
July-September, increasing thereafter throughout the winter to reach
maximum levels during the breeding season of April-June (Reproduction,
Fertility and Development 2000; 12(4) 229 - 235).
It is my hypothesis that DHEA is necessary for immune function. A number
of studies have demonstrated the effectiveness of DHEA against viral and
other infectious agents. Testosterone reduces conversion of DHEAS, the
background source of DHEA, to DHEA. Since DHEA may be involving in heat
production, cold weather should increase use of DHEA for heat. It is known
that avian viruses are increased by increased cold. Increasing levels of
testosterone during winter could explain why avian viruses increase during
the winter season. This could also explain why humans exhibit increased
vulnerability to viruses in the winter since testosterone increases in
autumn and winter in humans.