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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 (R(2) = 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., (© 2014 The American Society of Photobiology.)