Longitudinal Changes in Serum 25-Hydroxyvitamin D in the Dallas Heart Study

Abstract

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

2045 participants had serum 25(OH)D measured on two occasions (2000-2002 and 2007-2009) at a median interval of seven years. Serum 25(OH)D decreased (42.7 to 39.4 nmol/l, p<0.001) and the prevalence of vitamin D deficiency [25(OH)D < 50 nmol/l] increased significantly (60.6% to 66.4%, p<0.0001) despite vitamin D supplementation increasing over the interval (7.2% to 23.0%; p<0.0001). 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 < 0.0001), in participants of Hispanic ethnicity vs. White and Black ethnicity (p<0.0001), in non-obese vs. obese participants (-7.2 vs. -4.0 nmol/l, p=0.005), and in non-users vs. users of vitamin D supplements (-5.7 vs. -1.7 nmol/l, p=0.032).

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.

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