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