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Serum melatonin concentrations were determined by RIA in 81 healthy humans, aged 1–92 yr. The daytime (0900–1100 h) serum levels of melatonin decreased progressively with advancing age. No sex difference was noted. The nocturnal rise of serum melatonin in the aged group was significantly reduced compared with that in the young group. These results suggest that serum melatonin may be secreted under the agerelated neural control of pineal metabolism.
Iguchi et al. (Thu,) studied this question.