['Mono- and polyunsaturated fats may have opposing effects on vitamin D absorption.', 'The purpose of this study was to determine whether intakes of different dietary fats are associated with the increase in serum 25-hydroxyvitamin D (25OHD) after supplementation with vitamin D(3).', 'This analysis was conducted in the active treatment arm of a randomized, double-blind, placebo-controlled trial of vitamin D and calcium supplementation to prevent bone loss and fracture. Subjects included 152 healthy men and women age 65 and older who were assigned to 700 IU/d vitamin D(3) and 500 mg/d calcium. Intakes of monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), and saturated fatty acids (SFA) were estimated by food frequency questionnaire.', 'The change in plasma 25OHD during 2 yr vitamin D and calcium supplementation was assessed.', 'The change in plasma 25OHD (nanograms per milliliter) during vitamin D supplementation was positively associated with MUFA, (β = 0.94; P = 0.016), negatively associated with PUFA, (β = -0.93; P = 0.038), and positively associated with the MUFA/PUFA ratio (β = 6.46; P = 0.014).'] Is type of dietary fat associated with the 25-hydroxyvitamin D3 increment in response to vitamin D supplementation?