Circulating levels of leptin in different phases of the menstrual cycle - A systematic review and meta-analysis.

Leptin is a peptide hormone synthesized by white adipose tissue. Its principal site of action is in the brainstem and hypothalamus, where it acts to modulate satiety and control of reward and aversion. Leptin deficiency or resistance is associated with dysregulation of cytokine production, increased susceptibility to infections, autoimmune disorders, malnutrition, and inflammatory responses. Studies have shown variation in leptin levels between males and females, and in different phases of the menstrual cycle as well. Our study aims to explain the variation in leptin levels and their physiological role in the menstrual cycle. A total of 1887 records were identified from PubMed, Google Scholar, and Cochrane. We included studies where females were 18-40 years of age, who had achieved menarche, and were on regular menstrual cycles. We excluded studies which were cross-section, pre-prints, or studies where inadequate information was provided. Seven studies were included in the study. We used the standardized mean difference as the outcome measure. Leptin levels varied significantly in the phases of the menstrual cycle as well as during prepubertal, pubertal, and postpubertal phases. The standardized mean difference in leptin levels between the follicular phase and the luteal phase was 2.67 ng/mL (95% CI: 0.16 to 5.19 ng/mL). Fluctuations in leptin levels can cause weight changes and reproductive cycle disturbances. Hence, in cases of infertility with abnormal menstrual cycles, measurement of the physiologic variability in leptin levels may help to diagnose the cause of infertility and appropriate interventions can be started.