Clothing Practices and Vitamin D Status in Healthy Adults: A Systematic Review and Meta-Analysis

Vitamin D plays a vital role in bone health, immune function, and physiological well-being, with deficiency (VDD) being a widespread global concern. One proposed risk factor for VDD is body-covering clothing, including modest dress worn for religious, cultural, or personal reasons, which may reduce skin exposure to ultraviolet B radiation, potentially impairing endogenous vitamin D synthesis. This systematic review and meta-analysis examines the association between clothing practices and vitamin D in healthy adults. A literature search was conducted to identify studies from databases between 1 January 1975 and 1 January 2026. The inclusion criteria were healthy adults (18–65 years old), all genders, English-language, randomized controlled trials, observational studies, and full-text papers. The exclusion criteria included pregnancy, smoking, symptomatic VDD, acute illness, chronic diseases, and intake of medications affecting vitamin D metabolism. Overall, 2203 studies were identified, and 35 articles underwent full-text assessment. Twenty-seven studies were excluded due to ineligible populations and insufficient outcome data. Eight observational studies were included, comprising 1043 participants. In random-effects analysis, serum 25(OH)D was 12.8 nmol/L lower in covered than uncovered individuals (95% CI −21.7 to −3.8; z = −2.79, p = 0.005), with substantial heterogeneity (I2 = 93.7%; τ2 = 113.2; Q = 52.5, df = 5, p < 0.001). Newcastle-Ottawa assessment revealed three studies rated good, four fair, and one poor. This review highlights the need for targeted public health interventions, including supplementation and education, to mitigate VDD risk in individuals who wear modest clothing, particularly those residing in northern latitudes.