Plasma leptin concentrations are highly correlated to emotional states throughout the day

Previous work has shown that leptin appears to regulate the plasma levels of hormones such as adrenocorticotropic hormone (ACTH) and cortisol in humans and that it has antidepressant effects in animals. It is unknown whether fluctuations in circulating leptin levels are correlated to changes in human emotions. This study was conducted to determine whether minute-to-minute fluctuations in the plasma concentrations of human leptin were associated with psychological variables. Leptin was sampled every 7 min throughout the day in 10 healthy subjects (five men and five women) studied in a clinical research center, and visual analog scales were applied every hour. We found highly significant correlations between fluctuations in plasma leptin concentrations and three psychological variables: sadness, carbohydrate craving and social withdrawal. We showed that during the course of the day increases in leptin levels are associated with decreased search for starchy foods, decreased feelings of sadness and increased social withdrawal. Our findings support the hypothesis that during the course of the day as leptin levels increase individuals subjectively feel happier (less sad) and have less inclination to interact socially. Conversely, when leptin levels decrease, we show increases in sadness and social cooperation, which might facilitate the search for food. We suggest that increased human leptin levels may promote positive feelings and that decreased leptin levels might modulate inner states that motivate and facilitate the search for nutrients.