Seasonal Variation in Plasma L-Tryptophan Availability in Healthy Volunteers

Publisher Website
Google Scholar
Abstract
Objective: To investigate the seasonal variation in levels of plasmaL-tryptophan and competing amino acids (CAAs) in healthy humans in relation to climatic variables, total serum protein levels, and violent suicide occurrence. Methods: Twenty-six healthy volunteers (13 men and 13 women; mean [±SD] age, 38.7±13.4 years) had monthly blood samplings for assays ofL-tryptophan, valine, leucine, isoleucine, tyrosine, and phenylalanine during 1 calendar year. Results: Significant annual rhythms were detected inL-tryptophan, theL-tryptophan/CAA ratio, phenylalanine, valine, and leucine, and semiannual rhythms inL-tryptophan values and inL-tryptophan/CAA ratios. PlasmaL-tryptophan and theL-tryptophan/CAA ratio were significantly lower in the spring than in the other seasons. The peak-trough differences in the yearly variation expressed as a percentage of the mean were 17.1% and 16.1% forL-tryptophan values and L-tryptophan/CAA ratios, respectively. The amplitude of the yearly variation in all CAAs was low, ie, less than 7%. An important part of the variance inL-tryptophan availability (ie, 12% to 14%) could be explained by the composite effects of present and past climatic factors; higher ambient temperature and relative humidity in the face of lower air pressure are the most important predictors of lowL-tryptophan availability. Important and positive time relationships were noted between total serum protein level and all amino acid concentrations, and a significant time relationship was also noted between the seasonal variation inL-tryptophan availability and the occurrence of violent suicide in Belgium. Conclusion: Our results show a bimodal seasonal pattern in the availability of plasmaL-tryptophan that matches seasonal patterns in the prevalence of violent suicide in the local population and depression in other studies.

This publication has 33 references indexed in Scilit: