Personality Traits and Leptin

Leptin is an adipose-derived hormone that plays a significant role in food intake and energy storage by relaying information between peripheral tissue and the central nervous system. When functioning normally, leptin acts as a signal to the brain to stop eating. Higher levels of leptin typically reduce appetite, but the elevated level found in obese individuals is thought to be due to reduced sensitivity to leptin signaling (i.e., leptin resistance). In addition to its association with physiological factors such as obesity and inflammation (1), leptin has been implicated in a number of cognitive and psychological processes. Although leptin may have neuroprotective effects (2), elevated levels have been associated with poor psychological outcomes, including subjective stress (3) and post-traumatic stress disorder (4), although the findings are mixed on the association between leptin and depression (5, 6). There is reason to suspect that other psychological factors, specifically personality traits, may be related to circulating levels of leptin. Individuals high in Neuroticism and low in Conscientiousness are more prone to being overweight or obese (7-10), are more likely to experience weight fluctuations (10), have higher levels of inflammation (11, 12), and are more vulnerable to depression (13). The present study examines the association between personality and leptin in a large sample of community-dwelling adults. Given their association with obesity, inflammation, and psychological distress, we hypothesized that high Neuroticism and low Conscientiousness would be associated with higher levels of leptin. In addition to the five broad domains, we examine the association with more specific aspects, or facets of personality. We hypothesize that facets that have previously been linked to obesity (higher impulsiveness, higher assertiveness, lower activity, lower order, lower self-discipline, and lower deliberation) will be associated with higher leptin; we present the results for the remaining facets as exploratory analyses. We also examine whether the associations between personality and leptin are independent of body mass index (BMI), waist circumference, and inflammatory markers associated with both leptin and personality (interleukin-6 [IL-6], c-reactive protein [CRP], white blood cells [WBC]). Because the association between personality and leptin may depend on age and it may differ between the sexes, we examine whether these associations vary by age and sex. Finally, we hypothesize that the association between personality traits and adiposity will be partially mediated by higher levels of leptin.