Circannual rhythm in human sperm count revealed by serially independent sampling

Sperm concentration and total sperm counts from single semen and samples from each of 4435 patients requesting vasectomy between September 1972 and December 1977 were analyzed for circannual (about 1 year) rhythmicity. Although large temporal variations were found both between years and within years, a trend was noted for higher sperm concentration during the winter than during the summer. When the entire series of data were analyzed by months, a strong circannual pattern was apparent, with the highest sperm counts between February and March and the lowest counts during September. To the authors' knowledge, this is the first report of a circannual rhythm in human sperm concentration and total sperm count. The data must be considered preliminary, but if confirmed by other investigators studying comparable populations, the influence on clinical investigations will be profound.