Association of Fish Consumption with the Omega-3 Index and Vitamin D Status among Adolescent Females in the Southwest Coastal Zone of Bangladesh

Background: Omega-3 fatty acids (O3FA) and vitamin D are essential for growth, bone accrual, and neurodevelopment during adolescence and may affect future maternal and birth outcomes. Fish is a major dietary source of O3FA and vitamin D. However, evidence linking fish intake with O3FA and vitamin D status among adolescent females in Bangladesh remains limited. Objectives: This study aimed to investigate the associations of fish consumption with the Omega-3 Index (O3I) and serum 25-hydroxyvitamin D [25(OH)D] among adolescent females living across salinity gradients in southwest coastal Bangladesh. Methods: Two repeated cross-sectional surveys were conducted among 295 females during dry (August–September 2017) and wet (April–May 2018) seasons. Fish intake over the past week was assessed. Whole-blood eicosapentaenoic and docosahexaenoic acids were used to derive O3I, and serum 25(OH)D was measured. Associations between tertiles of fish intake and biomarker outcomes were examined using multivariable linear and logistic regression. Results: Mean O3I was 4.3% during dry season and 4.9% in wet season. Vitamin D insufficiency (<50 nmol/L) affected 25% of females during dry season and 39% in wet season. Compared with T1, adolescents in T3 of total fish intake had higher O3I (dry: β = 0.57; wet: β = 1.26) and greater odds of achieving O3I ≥4% [dry: adjusted odds ratio (AOR) = 2.12; wet: AOR = 7.98]. Tilapia consumption showed the strongest associations: females in T3 had higher O3I (dry: β = 1.08; wet: β = 1.63) and higher odds of O3I ≥4% (dry: AOR = 3.65; wet: AOR = 23.85). During wet season, higher total fish and tilapia intake were associated with higher 25(OH)D (β = 5.06 and 7.96) and lower odds of insufficiency for tilapia consumers (AOR = 0.25). Conclusions: Higher fish consumption, particularly tilapia, was associated with improved O3I and vitamin D status among adolescent females in coastal Bangladesh, with the strongest effects observed during wet season. Ensuring year-round access to diverse fish species, including saline-raised tilapia, may help address ω-3 and vitamin D insufficiency in this nutritionally vulnerable population.