[Do circannual rhythm of cortisol and testosterone interfere with variations induced by other events?]

Cortisol and testosterone are two hormones whose levels may vary in response to sports or occupational events. We wondered if the circannual rhythm of these hormones could have an influence on such responses or whether changes can always be ascribed to a single cause.

For cortisol, we conducted a cross-sectional study among 102 adult men (mean age 42 years) using saliva samples taken one half hour after awakening. The values were combined over three-month periods corresponding to the four seasons. For testosterone, conclusions were drawn from data reported in the literature.

The mean annual cortisol level was 14.36+/-0.44 nmol/l. There was no significant difference between average and peak values nor between maximal and minimal values. For testosterone, there have been a limited number of studies and it is unclear whether there is a seasonal change. In any case, the amplitude of variations is weak (9.7% between peak and annual average), which is partly ascribable to individual and interindividual variability.

We conclude that there is no seasonal (or circannual) rhythm in cortisol levels to a degree which could interfere with effects resulting from other events. For testosterone, the circannual rhythm may account for 10% of the variation.