Diurnal variation in salivary testosterone independent of food consumption

BackgroundWe previously reported that salivary testosterone (Sal T) decreased following a morning meal but concluded that this decrease could be a postprandial effect or an inherent circadian rhythm or both. Since no studies describing diurnal variations in Sal T have considered the effect of meals, we investigated the temporal variation of Sal T independent of food consumption.MethodsSalivary samples were collected from 17 males at 09.00 h, 10.00 h, and 11.00 h and then at 22.00 h, 23.00 h, and 24.00 h following an 8 h fast for each collection period.ResultsMean (standard deviation) Sal T concentrations were 191.2 (56.68) pmol/L at 09.00 h, 174.2 (53.29) pmol/L at 10.00 h, 168.1 (52.61) pmol/L at 11.00, 120.2 (46.04) pmol/L at 22.00 h, 130.3 (35.72) pmol/L at 23.00 h and 125.1 (29.75) pmol/L at 24.00 h. Sal T at 09.00 h was higher (<i>P</i> < .05) than at all other time points. Sal T at 10.00 h was similar (<i>P</i> = .65) to that at 11.00 h and both were higher (<i>P</i> < .05) compared to all evening time points. Although some patients exhibited a nadir in Sal T at 22:00 followed by an increase, overall evening levels were not significantly different (<i>P</i> > .80).ConclusionWe report an inherent circadian rhythm in Sal T with higher levels in the morning than evening and report for the first time that it is independent of food consumption.