Urinary 6-sulfatoxymelatonin excretion and aging: New results and a critical review of the literature

The apparent age-related decline in melatonin production has been thought t o continue in a secular manner across the lifespan. While it is clear that melatonin levels in children and adolescents are elevated compared to older individuals, the question of whether there is a sudden or gradual change h as not been adequately addressed. In this study, We report the excretion of the melatonin metabolite, 6-sulfatoxymelatonin in 253 subjects aged betwee n 21 and 82 yr. The correlation with age was significant (r = -0.24; P < 0. 05), When the data was analysed by ANOVA using 5-yr age spans, there was a significant effect of age, but post hoc analysis indicated that after 25 yr of age there was no significant decline in excretion of the metabolite. Th us, although the oldest subjects excreted 36% less melatonin metabolite tha n the youngest, the decrease occurred at a very early age. In the second pa rt of the study, we re-evaluated the data from seven precious studies that measured plasma melatonin levels or metabolite excretion across a wide rang e of ages and 11 studies comparing young versus older subjects. Statistical analysis by ANOVA again suggested that the changes in melatonin occurring with age were essentially complete before 30 yr of age. The youngest subjec ts produced at the most twice the amount of melatonin as the oldest subject s, Finally, we evaluated the mean plasma melatonin levels in 144 groups of normal subjects reported in 137 separate publications with respect to age. Again, whereas there was a significant correlation with age, ANOVA showed t hat there was no difference between groups after 35 yr of age, and the olde st groups had levels that were only 43% of the youngest groups, We conclude that melatonin production is lower in older people, but that the change oc curs very early in life, around 20-30 yr of age.