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. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive any funding ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study used ONLY openly available human data that were originally located at PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), and Google Scholar. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), and Google Scholar