Seasonal variation of the amino acid,
L-tryptophan, in interior Alaska

Levine ME, Duffy LK
Department of Psychiatry,
Fort Sam Houston, Texas, USA.
Int J Circumpolar Health 1998; 57 Suppl 1:386-8


The seasonal pattern of L-tryptophan was studied in a Fairbanks, Alaska, population that was unadapted to the extreme light variations of the North. Previously, this population was shown to exhibit seasonal behavior effects such as increases in fatigue and sleep duration, as well as endocrine effects such as increases in melatonin levels and phase shifting. Caloric and macronutrient intake have been reported to vary seasonally in humans, thereby potentially influencing the plasma levels of L-tryptophan, which is a precursor of serotonin and melatonin. Plasma levels of L-tryptophan from volunteers, whose average duration of stay in Alaska was eight months, were determined by automated amino acid analysis. Prominent results included finding increased levels in the winter at several different diurnal time points. These findings support hypotheses which relate underlying physiological adaptations to the North to the increased incidence of behavioral disorders such as depression and alcoholism.

Light therapy
Winter depression
Tryptophan depletion
Tryptophan plus fluoxetine
Tryptophan and alcoholism
Tryptophan/antidepressant response
5-HTP and l-tryptophan as antidepressants
Alcohol, suicide and tryptophan hydroxylase
Tryptophan and 5-hydroxytryptophan for depression
Tryptophan/serotonin depletion and reward cue processing

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