Effect of Obesity on Inflammation Fluctuations During the Menstrual Cycle: An Analysis of the Cross-Sectional Study of NHANES

Background: Inflammation during the menstrual cycle can be influenced by obesity. This study aimed to determine the effect of obesity on systemic inflammation during the menstrual cycle. Methodology: We analysed National Health and Nutrition Examination Survey (NHANES; 1999–2006) data from biological females aged 18–45 years with body mass index (BMI) between 18.5 and 40.0 kg/m², available data on days since last menstrual period, and complete blood counts. Participants were categorized as normal weight (18.5–24.9 kg/m²) or overweight/obese (25.0–40.0 kg/m²). Periodicity was assessed using R (v4.4.0) with the Cosinor and Cosinor2 packages to estimate the midline estimation statistic of rhythm (MESOR), representing the rhythm-adjusted mean, amplitude (half the predictable peak-to-trough variation), and acrophase (peak timing). Results: BMI stratification revealed differences in platelet, neutrophil, and leukocyte counts, but not monocyte counts, leading to significant differences in the neutrophil–lymphocyte–platelet ratio (NLPR), systemic inflammation response index (SIRI), C-reactive protein (CRP) to albumin ratio, aggregate index of systemic inflammation, and systemic immune-inflammation index (SII). Cosinor analysis showed significant rhythmicity for NLPR and SIRI (p<0.001). Amplitudes were similar across BMI groups; however, MESORs and acrophases differed for NLPR (p<0.05). For SIRI, amplitudes and MESORs were similar, but acrophases differed between BMI groups (p<0.05) Conclusion: Inflammation during the menstrual cycle has periodicity, and obesity affects the overall midline of inflammation and the time at which the peak inflammation occurs. This is the first study to characterize the inflammatory fluctuations associated with the menstrual cycle and examine how they are affected by obesity.