Longitudinal changes in serum 25-hydroxyvitamin D in the Dallas Heart Study

Context: While the prevalence of vitamin D deficiency is well described in various populations, limited data are available regarding longitudinal variation in serum 25-hydroxyvitamin D concentrations. Objectives: To evaluate the temporal trends in serum 25(OH)D, prevalence of vitamin D deficiency and factors influencing these trends. Participants, Design and Setting:: Adults enrolled in the Dallas Heart Study, a longitudinal, probability-based, multiethnic, population study in Dallas, Texas, USA. Main Outcome Measures: Prevalence of vitamin D deficiency and predictors of change in serum 25(OH)D. Results: A total of 2045 participants had serum 25(OH)D measured on two occasions (2000-2002 and 2007-2009) at a median interval of 7 years. Serum 25(OH)D decreased (42.7-39.4 nmol/L, P<.001) and the prevalence of vitamin D deficiency [25(OH)D <50 nmol/L] increased significantly (60.6%-66.4%, P<.0001) despite vitamin D supplementation increasing over the interval (7.2%-23.0%; P<.0001). In a multivariable model adjusting for sex, race, BMI, age, season of blood draw, smoking and exercise, a greater decline in serum 25(OH)D was noted in men compared with women (−8.0 vs −3.5 nmol/L, P<.0001), in participants of Hispanic ethnicity vs White and Black ethnicity (P<.0001), in nonobese vs obese participants (−7.2 vs −4.0 nmol/L, P=.005) and in nonusers vs users of vitamin D supplements (−5.7 vs −1.7 nmol/L, P=.032). Conclusions: Despite increased vitamin D supplementation, serum 25(OH)D decreased in an ethnically diverse cohort of Dallas County residents between 2000-2002 and 2007-2009. Features most predictive of a decline in serum 25(OH)D include male sex, Hispanic ethnicity and weight gain.