Frequency of leisure-time physical activity and serum 25-hydroxyvitamin D levels in the US population: results from the Third National Health and Nutrition Examination Survey

Abstract

The decline in vitamin D status among older people is probably due to decreased synthesis of vitamin D by sun-exposed skin and/or decreased outdoor activity. The authors examined the association between outdoor leisure physical activity and serum 25-hydroxyvitamin D in the Third National Health and Nutrition Examination Survey (1988-1994) (n = 15,148 aged >/=20 years). The mean 25-hydroxyvitamin D concentration declined with increasing age, with 79, 73, and 68 nmol/liter for persons aged 20-39, 40-59, and 60 or more years. The proportion that engaged in outdoor activity in the past month was 80% for persons aged 20-39 and 40-59 years but 71% for those aged 60 or more years. In contrast, the mean difference in 25-hydroxyvitamin D between those who participated in outdoor activities daily compared with those who did not participate in the past month was similar for the youngest and oldest age groups: 13 and 16 nmol/liter, respectively. Those persons aged 60 or more years who participated in daily outdoor activities had a mean 25-hydroxyvitamin D concentration similar to that of persons aged 20-39 years: 77 versus 79 nmol/liter, respectively. These nationally representative data suggest that persons aged 60 or more years can synthesize enough vitamin D from daily outdoor activities to maintain vitamin D levels similar to those of young adults.

FIGURE 1.

Mean (95% confidence interval) difference in serum 25-hydroxyvitamin D concentration associated with frequency of outdoor activity in the past month, compared with no outdoor activity, by age group, adjusted for sex, ethnicity, body mass index, month, milk, cereal, and vitamin D supplements, Third National Health and Nutrition Examination Survey, 1988–1994. Solid bars, reference; striped bars, mean difference.

FIGURE 2.

Mean (95% confidence interval) difference in serum 25-hydroxyvitamin D concentration associated with frequency of outdoor activity in the past month, compared with no outdoor activity, by ethnic group, adjusted for sex, age, body mass index, month, milk, cereal, and vitamin D supplements, Third National Health and Nutrition Examination Survey, 1988–1994. Solid bars, reference; striped bars, mean difference.