Relationship between abdominal obesity (based on waist circumference) and serum vitamin D levels: a systematic review and meta-analysis of epidemiologic studies

Context Although previous observational studies have investigated the association between waist circumference (WC) values and serum vitamin D levels, findings have been inconsistent. Objective A systematic review and meta-analysis was performed to evaluate the effect of abdominal obesity (based on WC) on vitamin D deficiency or insufficiency in adults. Data Sources A systematic search of the published literature up to September 2020 was conducted in electronic databases, including MEDLINE (PubMed), EMBASE, Institute for Scientific Information (ISI) (Web of Science), Scopus, and Google Scholar, for observational studies that investigated the association between abdominal obesity (based on WC) or different categories of WC as the exposure and serum 25-hydroxy vitamin D levels as the outcome. Data Extraction Eighteen cross-sectional studies were included in the review. The relationship between WC values and combined serum vitamin D deficiency and insufficiency (<30 ng/mL) or vitamin D deficiency (<20 ng/mL) was evaluated. Data Analysis Combining 8 effect sizes from 5 investigations, including 7997 individuals, illustrated that the highest category of WC, compared with the lowest category of WC, was related to 82% increased odds of combined serum vitamin D deficiency and insufficiency (<30 ng/mL) (OR: 1.82; 95% CI: 1.34, 2.49). Moreover, in studies that investigated both genders together, the highest category of WC, compared with the lowest category of WC, was associated with 61% increased odds of serum vitamin D deficiency (<20 ng/mL) (OR: 1.61; 95% CI: 1.12, 2.31). The same results were obtained for almost all subgroups for several covariates. Conclusion This meta-analysis of cross-sectional studies confirmed that increased WC was related to the elevated risk of combined vitamin D deficiency and insufficiency in adults. More prospective studies are needed to confirm causality. Systematic Review Registration PROSPERO registration no. CRD42020190485.