Leptin, Somatic Depressive Symptoms and the Metabolic Syndrome: a Comment on Chirinos et al.
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INVITED COMMENTARY
Leptin, Somatic Depressive Symptoms and the Metabolic Syndrome: a Comment on Chirinos et al. Javier Labad, M.D., Ph.D. & Rebecca M. Reynolds, Ph.D.
Published online: 20 March 2013 # The Society of Behavioral Medicine 2013
People with depression are at increased risk of metabolic syndrome and vice versa [1]. Leptin, a hormone secreted by adipose tissue is a plausible link as levels are increased in people with obesity and depression [2, 3]. The article by Chirinos et al. [4] replicates previous findings and adds new evidence to the field: the association of circulating leptin levels with somatic depressive symptoms. In the study by Chirinos et al. [4], somatic but not cognitive depressive symptoms were associated with increased plasma leptin levels in 135 subjects with metabolic syndrome. These results, together with another recent study linking somatic depressive symptoms with C-reactive protein, interleukin-6 and tumour necrosis factor-α levels [5] suggest that adipokines and inflammatory markers may have a pathogenic role in the expression of somatic depressive symptoms. Interestingly, the association between leptin and somatic depressive symptoms was only found in men [4], which is in accordance with other studies reporting sex differences in the relationship between leptin and depressive symptoms [3], especially in socially isolated men [6]. We have also found a positive association between leptin and poorer neuropsychological performance in men with type 2 diabetes [7]. As animal models suggest that brains of male and female rats are differentially sensitive to the effects of leptin, with reduced effects in male rats [8], it is plausible that the association between leptin and neuropsychiatric symptoms in men may be explained by sex J. Labad (*) Hospital Universitari Institut Pere Mata, IISPV, Universitat Rovira i Virgili. CIBERSAM, Ctra. de l’Institut Pere Mata, s/n, 43206 Reus, Spain e-mail: [email protected] R. M. Reynolds (*) Endocrinology Unit, University/BHF Centre for Cardiovascular Science, Queen’s Medical Research Institute, University of Edinburgh, Edinburgh EH16 4TJ, UK e-mail: [email protected]
differences in leptin sensitivity at key brain areas (e.g., hypothalamus, hippocampus). Of all different somatic symptoms, Chirinos et al. found appetite disturbances, fatigue and sleep difficulties were associated with higher leptin levels [4]. Insomnia is a prevalent symptom in major depression and lack of sleep is also thought to be a risk factor for obesity and metabolic syndrome [9]. Anatomical factors related to obesity (reduced pharyngeal lumen size, decreased upper airway muscle force, reduced upper airway size) may cause obstructive sleep apnoea, which contributes to sleep difficulties. However, other patients with obstructive sleep apnoea show instability in ventilatory control that exacerbates otherwise minor anatomical deficits [10]. Hormonal factors secondary to obesity may also contribute to sleep disturbances. Increased serum leptin levels are associated with reduced r
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