Seasonal variations of lithium plasma levels

The aim of this study was to investigate the seasonal time course of lithium blood levels. We analyzed lithium plasma and red blood cell (RBC) levels in 186 subjects affected by bipolar (n=134) and major depressive (n=52) disorder, with stable oral dosage, followed in our lithium clinic for an average of 36 months. We observed a significant elevation of lithium plasma levels in summer with a more marked variation among early-onset subjects, bipolar subtype, and females. Lithium levels in plasma peaked in summer, and levels in RBC showed a trend in the same direction. Possible stratification factors such as presence of affected relatives or psychotic features did not significantly influence results. In conclusion, we observed a significant variation of lithium plasma levels according to seasons. If confirmed, this finding could have both clinical and research implications.