Low 25-hydroxyvitamin D levels in adolescents: race, season, adiposity, physical activity, and fitness

Abstract

Objectives: The objectives were to characterize the vitamin D status of black and white adolescents residing in the southeastern United States (latitude: approximately 33 degrees N) and to investigate relationships with adiposity.

Methods: Plasma 25-hydroxyvitamin D levels were measured with liquid chromatography-tandem mass spectroscopy for 559 adolescents 14 to 18 years of age (45% black and 49% female). Fat tissues, physical activity, and cardiovascular fitness also were measured.

Results: The overall prevalences of vitamin D insufficiency (<75 nmol/L) and deficiency (< or = 50 nmol/L) were 56.4% and 28.8%, respectively. Black versus white subjects had significantly lower plasma 25-hydroxyvitamin D levels in every season (winter, 35.9 + or - 2.5 vs 77.4 + or - 2.7 nmol/L; spring, 46.4 + or - 3.5 vs 101.3 + or - 3.5 nmol/L; summer, 50.7 + or - 4.0 vs 104.3 + or - 4.0 nmol/L; autumn, 54.4 + or - 4.0 vs 96.8 + or - 2.7 nmol/L). With adjustment for age, gender, race, season, height, and sexual maturation, there were significant inverse correlations between 25-hydroxyvitamin D levels and all adiposity measurements, including BMI percentile (P = .02), waist circumference (P < .01), total fat mass (P < .01), percentage of body fat (P < .01), visceral adipose tissue (P = .015), and subcutaneous abdominal adipose tissue (P = .039). There were significant positive associations between 25-hydroxyvitamin D levels and vigorous physical activity (P < .01) and cardiovascular fitness (P = .025).

Conclusions: Low vitamin D status is prevalent among adolescents living in a year-round sunny climate, particularly among black youths. The relationships between 25-hydroxyvitamin D levels, adiposity, physical activity, and fitness seem to be present in adolescence.

Figure 1

Age-adjusted mean ± SE plasma 25-hydroxyvitamin D[25(OH)] concentrations by season in white females (n = 36, 37, 27, and 55 for winter, spring, summer, and fall, respectively), black females (n = 18, 37, 36, and 31 for winter, spring, summer and fall, respectively), white males (n = 22, 53, 29, and 51 for winter, spring, summer and fall, respectively), and black males (n = 33, 53, 23, and 21 for winter, spring, summer and fall, respectively). Significant main effects of season, race, and sex were observed, but no significant interaction between season, race, and sex was observed. Means between seasons were significantly different for each race and marginally different when averaged over race (P < 0.05). Means between races were significantly different for winter, spring, summer, and fall and marginally different when averaged over seasons (whites > blacks; P < 0.05). Means between sex were significantly different for fall only (males > females; P = 0.03). Plasma 25(OH)D concentrations were log-transformed prior to analyses.