Prevalence of Vitamin D Deficiency in Healthy Adults: A Systematic Review and Meta-Analysis

Vitamin D deficiency is a growing global public health concern, linked to increased mortality and various diseases, including cancer, heart disease, diabetes, and depression. This systematic review and meta-analysis analyzed studies from 2003 to 2023 to estimate the prevalence of vitamin D deficiency among healthy adults worldwide. According to previous reports, serum 25(OH)D levels below 20 ng/mL (50 nmol/L) are generally classified as deficient, while concentrations between 20 and 30 ng/mL (50–75 nmol/L) are considered insufficient, and levels above 30 ng/mL (≥ 75 nmol/L) are regarded as sufficient. However, some studies define levels below 12 ng/mL (30 nmol/L) as severe deficiency, 12–20 ng/mL (30–50 nmol/L) as insufficiency, and ≥ 20 ng/mL (≥ 50 nmol/L) as sufficient. In addition, other sources suggest that serum concentrations below 30 ng/mL (75 nmol/L) may also indicate a deficiency threshold. Findings reveal that 51.1% of healthy adults are vitamin D deficient, with higher rates in women (56.8%) than men (43.7%). The prevalence varies by region: Africa (54.2%), America (34.3%), Europe (51.6%), Western Pacific (44.9%), Eastern Mediterranean (highest at 62.7% in women), and Southeast Asia (55.3%). The lowest deficiency rates are in America, where one in three individuals is affected. Women, particularly in the Eastern Mediterranean region, consistently show higher deficiency rates compared to men. These findings underscore the need for region-specific strategies, including awareness campaigns led by health organizations, increased sun exposure, vitamin D supplementation, and food fortification.