To complicate matters, testosterone levels fluctuate and peak around 8 in the morning. Levels tend to be lowest around 8 p.m., and then rise during the night. Peaks and valleys are larger for men 40 years old or younger compared to men in their 70s. Testosterone secretion has a diurnal secretion pattern.
Maximum levels are reached in the morning between 07:00 and 10:00 a.m., a minimum is observed at night and levels begin to rise again at night.10 One study found that young men (30 to 40 years old) had an average of 88.00 testosterone levels (both free and total), which were 30 to 35% higher than levels measured in the middle of the afternoon or late afternoon. This difference decreased with age and fell to approximately 10% by age 70. 11 This decrease in the circadian rhythm of testosterone with normal aging is well described. 12 Other hormones and substances were also measured, such as insulin, leptin, sex hormone binding globulin (SHBG) and total testosterone levels.
The guidelines recommend collecting a sample first thing in the morning to compensate for the natural daytime variation in testosterone levels. This study shows how eating a 550-calorie meal containing proteins, fats and carbohydrates can influence testosterone levels. Pathology tests performed at the wrong time of day waste resources, cause inconvenience, and can cause anxiety in both health professionals and patients when they try to interpret useless results. The authors recommend that men with erectile dysfunction who are 45 years old can have their total testosterone removed any time before 2 in the afternoon.
In a retrospective analysis of 2,569 patients of men with erectile dysfunction to measure total testosterone and extraction times, men were compared by age group and variability of total testosterone. Other hormones and parameters remained the same, only that the levels of total and bioavailable testosterone decreased significantly. A simple glucose load can significantly lower total testosterone levels and falsely qualify a person as hypogonadism. Because the natural daytime variation in testosterone levels tends to decrease with age, it's acceptable to test men age 45 or older before 2 p.m.
However, some studies suggest that fasting before a testosterone test can significantly alter final results. These findings also involve re-evaluating subjects who were initially diagnosed with low testosterone levels. Bremner, the circadian variation of testosterone, the globulin that binds to sex hormones and the calculated testosterone bound to the non-sexual globulin that binds to sex hormones in healthy young and old men. This reveals that the behavior of the hypothalamic-pituitary-testicular (HPT) axis was not really affected by food or glucose intake, but testosterone production was affected.