Sex-Specific Age-Associated Patterns of Vitamin D Status in Urban Ethiopia: A Cross-Sectional Analysis of the Ethiopian Paradox

Background Vitamin D deficiency persists in sub-Saharan Africa despite abundant sunlight—a phenomenon termed the "Ethiopian Paradox." Whether age-associated patterns of vitamin D status are sexually dimorphic remains poorly understood. Methods A retrospective cross-sectional study of 1,079 apparently healthy Ethiopian adults (606 females, 473 males) was conducted. Serum 25(OH)D was measured via CMIA (Abbott Alinity i). We employed status-stratified correlations, quantile regression, Fisher's Z-transformation, and sensitivity analyses across diagnostic thresholds to evaluate age-associated cross-sectional patterns. Results Overall deficiency (< 20 ng/mL) was 39.1%, significantly higher in women (45.4%) than men (30.9%; p < 0.001). Age-stratified analysis revealed an age-associated attenuation of the male protective pattern: young women (18–29 years) had 52.2% deficiency vs. 23.6% in men (p = 0.002); by age 60+, prevalence converged (40.9% vs. 37.1%; p = 0.511). Within the deficient subgroup, men exhibited a significant inverse relationship with age (slope: −0.046 ng/mL/year; ρ=−0.279, p = 0.0006), while women maintained a stable plateau (ρ=−0.081, p = 0.178). Fisher's Z confirmed sex divergence in correlation magnitudes (Z = − 2.354, p = 0.0186), though the formal age×sex interaction term was trend-level (β=−0.033, p = 0.072). Sex-stratified quantile regression revealed that deficient males show uniform decline across the entire distribution (10th percentile: −0.067, p = 0.002; 50th percentile: −0.052, p = 0.004), while deficient females show stability at both the lower tail and the median. The Gini coefficient within the deficient subgroup remained stable across age deciles (0.091–0.126), ruling out concentration of severe deficiency in older age. Diagnostic threshold analysis revealed that 4.8% met IOM criteria (< 12 ng/mL) vs. 39.1% under Endocrine Society criteria (< 20 ng/mL), with the largest gap (47.3 percentage points) in women aged 50–59 years. Conclusion Vitamin D deficiency manifests as distinct sex-specific cross-sectional patterns: an inverse age-associated decline in men versus a stable plateau in women, observed predominantly below a 20 ng/mL statistical threshold. These patterns reflect uniform decline in deficient males—not selective lower-tail deterioration—and stability in deficient females. These findings warrant hypothesis-testing in prospective cohorts to inform sex-specific, threshold-informed screening strategies.