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Reproductive Function during Summer and Winter in Norwegian Men Living North and South of the Arctic Circle

Fertility Centre (G.M., A.G.), Scanian Andrology Centre, University Hospital MAS, Malmö, SE 205 02 Sweden; Andrology Laboratory (T.B.H., T.H., C.B., T.S.), Department of Gynaecology and Obstetrics, Rikshospitalet University Hospital, N-0027 Oslo, Norway; The Cancer Registry of Norway (T.G.), Institute of Population-Based Cancer Research, N-0310 Oslo, Norway; Department of Clinical Chemistry (J.M.), University Hospital MAS, SE 205 02 Malmö, Sweden; Department of Clinical Chemistry (Y.F.), University Hospital of North Norway, N-9038 Tromsoe, Norway; Department of Occupational and Environmental Medicine (L.H., L.R.), Lund University Hospital, Sweden; and Department of Health and Human Services (R.J.L.), National Institute of Child Health and Human Development, Bethesda, Maryland 20892

Address all correspondence and requests for reprints to: Aleksander Giwecman, M.D., Fertility Center, Scanian Andrology Centre, Malmö University Hospital, SE 205 02, Malmö, Sweden. E-mail: aleksander.giwercman{at}kir.mas.lu.se.

Seasonal, daylight-dependent variation in human spermatozoa counts, with lowest values during summer, has been suggested. To test this hypothesis, we performed a longitudinal study of semen quality and reproductive hormone levels in Norwegian men living north and south of the Arctic Circle. An ejaculate and a serum specimen were obtained both in summer and in winter from 92 volunteers in Tromsoe (69° north latitude) and 112 in Oslo (60° north latitude). Semen analyses were performed, and serum was assayed for FSH and inhibin B. The median spermatozoa concentration in Tromsoe after adjustment for abstinence period length was 49 x 10⁶/ml in summer and 54 x 10⁶/ml in winter. Corresponding values for Oslo were 59 x 10⁶/ml and 54 x 10⁶/ml. The seasonal differences in spermatozoa concentration were not statistically significant, nor were significant differences observed in median total spermatozoa count, semen volume, percentage progressive motile spermatozoa, or FSH. In Tromsoe, but not Oslo, inhibin B concentration was slightly, but significantly (P = 0.02) higher in winter than summer (229 ng/liter vs. 223 ng/liter).

The length of the daylight period may have a slight impact on hormonal markers of spermatogenesis but does not cause substantial changes in spermatozoa numbers and motility.

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