Vitamin D deficiency is more common in Northeast-Asian immigrants to western countries than in the local population; prevalence equalizes as immigrants adopt the host country's culture. In a community-based study of 100 Northeast-Asian immigrants in Canberra, Australia, we examined predictors of vitamin D status, its association with indicators of acculturation (English language use; time since migration) and mediators of that association. Participants completed a sun and physical activity diary and wore an electronic ultraviolet radiation ( UVR) dosimeter for 7 days. Skin colour was measured by reflectance spectrophotometry. Serum concentrations of 25-hydroxyvitamin D (25( OH)D) and cardio-metabolic biomarkers were measured on fasting blood. In a multiple linear regression model, predictors for 25( OH)D concentration were season of blood collection, vitamin D supplementation, UVR exposure, body mass index, physical activity and having private health insurance ( R2 = 0.57). Greater acculturation was associated with lower risk of vitamin D deficiency (de-seasonalized 25( OH)D level <50 nmol L−1) (Adjusted Odds Ratio ( AOR): 0.22 [95% CI 0.04-0.96]); this association was statistically mediated by physical activity and time outdoors. Vitamin D deficiency was associated with higher total cholesterol levels (>5.0 mmol L−1) ( AOR: 7.48 [95% CI 1.51-37.0]). Targeted public health approaches are required to manage the high prevalence of vitamin D deficiency in migrants retaining a traditional lifestyle. [ABSTRACT FROM AUTHOR]