Association of Vitamin D Levels and Muscle Mass Reduction in Women of Childbearing Age: NHANES 2011–2018

Background: Currently, vitamin D deficiency is highly prevalent among women of childbearing age. However, the relationship between vitamin D levels and muscle mass reduction in women of childbearing age remains unclear. This study aimed to investigate the association between vitamin D levels and muscle mass reduction in women of childbearing age. Methods: This study included 3934 participants from the National Health and Nutrition Examination Survey (NHANES) 2011–2018. Weighted linear regression and weighted chi-square tests were used to compare baseline characteristics between groups for continuous and categorical variables, respectively. Weighted logistic regression analysis was employed to assess the association between vitamin D levels and muscle mass reduction. Results: The study population was divided into two groups, 2803 non-muscle mass reduction and 1131 muscle mass reduction participants. The quartile of appendicular skeletal muscle mass (ASM)/body mass index (BMI) for diagnosing muscle mass reduction was determined to be 0.579. Compared with the non-muscle mass reduction group, muscle mass reduction women of childbearing age had a higher prevalence of vitamin D deficiency (p < 0.001) and lower use of vitamin D supplements (p = 0.018). Serum vitamin D levels in the muscle mass reduction group were significantly lower than those in the non-muscle mass reduction group (p < 0.001). After adjusting for confounding variables, weighted logistic regression analysis revealed that insufficient (odds ratio (OR) = 1.34, 95% confidence interval (CI): 1.01–1.78, p = 0.042) and deficient (OR = 1.54, 95% CI: 1.16–2.05, p = 0.003) vitamin D levels were still associated with muscle mass reduction. Conclusions: Insufficient and deficient vitamin D levels are associated with muscle mass reduction in women of childbearing age, highlighting the potential role of vitamin D in muscle mass reduction management. Vitamin D supplementation may improve muscle mass reduction in vitamin D-deficient women of childbearing age, and its effectiveness needs to be further verified by randomized controlled trials.