Synchronized
Seasonal Variation in Plasma Melatonin and Plasma Tryptophan
and the Immune System by Michael Maes, Simon Scharpé, Robert Verkerk, Wim
Stevens, Dirk Peeters &
Peter D’Hondt Key words: melatonin; seasonality; tryptophan; lymphocytes; immunity
Abstract:
The
purpose of this study was to examine the seasonal variation
in plasma melatonin concentrations in relation to the availability
of plasma tryptophan and the absolute number of lymphocyte subtypes
in normal humans. Towards this end, 26 normal volunteers (13
men, 13 women) had monthly blood samplings for melatonin, immune
and amino-acids assays during one calendar year. A significant
seasonal variation is observed in plasma melatonin levels with
semiannual and tetramensual rhythms. The seasonal variation
in plasma melatonin is synchronized with that in the availability
of plasma tryptophan and with that in the number of peripheral
blood CD3+ T, CD4+ T, and CD20+ B lymphocytes. The findings
suggest that the seasonal variation in plasma melatonin is synchronized
by the seasonal rhythm in the availability of plasma tryptophan
to the brain, and that melatonin may modulate the seasonal variations
in the immune system.
