Circannual and circadian rhythms in plasma testosterone in five healthy young Parisian males

Every other month, during the course of 14 months, the circadian rhythm in plasma testosterone (among others variables) of 5 healthy males (26 to 32 years) was documented. Subjects' synchronization: light-on at 7 +/- 1 h; light-off at 23 +/- 1.5 h during the whole year. Blood sampling 4-hourly, at fixed times during 28 h, for radioimmunological testosterone determinations. The cosinor method was used for statistical analyses. An annual rhythm in the testosterone 24-h mean is detected (P less than 0.025) with a peak in October (from 16 July to 26 December, with 95% confidence limits). Annual mean (+/-1 se)= 759 (+/- 26) ng/100 ml. Peaktrough difference=197 ng/100 ml (from 106 to 290 with 95% confidence limits). The timing of the testosterone circadian peak, in the 24-h-scales also varies during the course of the year. The peak is found around 8 h in May and around 14 h in November, this phase-shift being statistically significant (P less than 0.05).