Androlog Mail:
In response to Dr. Hawkes:
Sperm concentration in studies conducted at a variety of locations in
the northern hemisphere appears to be highest in late winter (February,
March) and during fall (November), but lower during July, August, and
September. The phenomenon observed by Dr. Hawkes may well have
reflected seasonal variation, although the decline of more than 50
percent seems excessive. Eleven men seems to be a small sample to
observe even within-person changes in semen quality. Thus the large
decline in sperm count could reflect both seasonal variation and chance
variation. Similar before-after study designs within a similar calendar
month period of study have also shown large declines in sperm
concentration in occupational studies conducted in Denmark and reported
in December at the International Symposium on Environment, Lifestyle,
and Fertility in Aarhus, Denmark.
For further information, you may wish to read:
Levine RJ: Male factors contributing to the seasonality of human
reproduction. Ann NY Acad Sci 1994;709:29-54.
...
I neglected to mention earlier that the most likely cause of seasonal
variation in human sperm counts appears to be an internal biological
clock fine-tuned by seasonal change in photoperiod - i.e. not heat.
Rhesus monkeys kept under constant laboratory conditions including 12
hr. light / 12 hr. dark cycles maintain seasonality of male reproductive
function for at least 4 years. These animals also show pronounced
changes in testicular volume with changes in photoperiod (increased with
8 hr light / 16 hr dark cycles; decreased with 16 hr light / 8 hr dark
cycles)
Wickings EJ, Nieschlag E: Seasonality in endocrine and exocrine
testicular function of the adult rhesus monkey (Macaca mulatta)
maintained in a controlled laboratory environment. Int J Androl
1980;3:87-104.
Chik CL, Almeida OFX, Libre EA et al: Photoperiod-driven changes in
reproductive function in male rhesus monkeys. J Clin Endocrinol Metab
1992;74:1068-1074.
Levine RJ (cf. below).
RICHARD LEVINE
RL44W@NIH.GOV
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