The Baltimore Longitudinal Aging Study25 reported the levels of various sex hormones and gonadotropins, and testosterone response to hCG, in 69 healthy men aged 25-89 years. This study failed to show any effect of age on levels of serum testosterone, 5α-DHT, estrone, and estradiol. There was an increase in serum binding of testosterone in response to an elevated SHBG but no change in the free T index. The authors noted a slightly elevated basal LH and a blunted testosterone response to hCG with aging that suggested a small peripheral resistance to LH at the level of the Leydig cell. They concluded that the effect of age-related illnesses were more responsible for the decreases in sex hormones reported by previous studies considering the excellent health of the study subjects. One criticism of this study is that blood was collected in the afternoon when the natural circadian rhythm would be at its nadir.