Leisure-time Physical Activity and Serum 25-Hydroxyvitamin D Levels
Leisure-time Physical Activity and Serum 25-Hydroxyvitamin D Levels
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.
Increasing evidence suggests that low vitamin D status is a risk factor for a range of diseases, including bone disease, infection, cancer, diabetes, and cardiovascular disease. A recent meta-analysis of 18 randomized trials including more than 57,000 participants demonstrated a significant reduction in all-cause mortality among older individuals assigned to vitamin D supplements. Sun exposure is the primary determinant of vitamin D status, but age and the degree of skin pigmentation are known to modify the effect of the sun on vitamin D synthesis.
Since the late 1970s, researchers have noted that body levels of vitamin D, as measured by serum 25-hydroxyvitamin D, decline with age. This decline is due partly to a decreased capacity by the epidermis of the elderly to photosynthesize previtamin D, as compared with younger subjects, but the decline also may be due to decreased sun exposure because sun tanning and sun burning decrease with age.
Racial/ethnic variations in vitamin D status also occur, with lower levels observed in non-Hispanic Blacks and Mexican Americans compared with non-Hispanic Whites. Vitamin D insufficiency (serum 25-hydroxyvitamin D, <50 nmol/liter) is much more common among non-Hispanic Blacks (in winter ranging from 53 percent to 76 percent across the main age-sex subgroups) than in Mexican Americans (18-50 percent) and non-Hispanic Whites (8-33 percent). Studies of vitamin D photosynthesis have shown that non-Whites have a similar capacity to synthesize vitamin D, but they require longer exposure to sunlight to achieve a similar vitamin D response because of their increased skin pigmentation.
Outdoor activities increase body vitamin D levels through sun-induced synthesis of vitamin D. Previous studies have shown a positive association between physical activity, in general, and vitamin D status. Blood levels of 25-hydroxyvitamin D have been observed to be higher in weightlifters and track athletes than matched sedentary controls in some studies but not all. The cited studies had small sample sizes (n < 60) that may have decreased power to detect an association between physical activity and 25-hydroxyvitamin D.
Few epidemiologic studies have examined the relation between leisure-time physical activity and vitamin D status in the general population. In the early 1990s, a cross-sectional survey of middle-aged men in New Zealand found that men who engaged in weekly leisure-time aerobic activities (indoor and outdoor combined) had significantly increased plasma levels of 25-hydroxyvitamin D compared with inactive men after adjustment for weekly hours of sunshine exposure, especially in winter. In a healthy workforce sample, also in New Zealand, the mean level of serum 25-hydroxyvitamin D3, the vitamin D metabolite formed mainly from sun exposure and which comprises the major portion of body vitamin D, was higher in people engaging in vigorous (aerobic) leisure physical activities compared with those who were inactive, after adjustment for age, sex, ethnicity, and time of year; moreover, serum 25-hydroxyvitamin D3 was 11-13 nmol/liter higher in those who participated in outdoor versus indoor activities. Recent reports have confirmed these earlier findings. Analyses of male US health professionals showed that participants in the highest quintile of leisure-time physical activity had a 13.5 nmol/liter higher level of plasma 25-hydroxyvitamin D than those in the lowest activity quintile. A cross-sectional survey in Florida found that osteoporosis patients who reported participating in outdoor exercise were 47 percent less likely to have hypovitaminosis D (25-hydroxyvitamin D, ≤30 ng/ml or 75 nmol/liter) than were nonoutdoor exercisers. Finally, Dutch studies of older people living in the community have observed a positive association between the level of physical activity and serum 25-hydroxyvitamin D and reported that serum 25-hydroxyvitamin D increased by 1.8 nmol/liter for each hour per day of outdoor activity.
The Third National Health and Nutrition Examination Survey (NHANES III) involved a representative sample of the US civilian population, who were interviewed during 1988-1994. With serum 25-hydroxyvitamin D measurements from over 19,000 participants, NHANES III offers a unique opportunity to examine the association between leisure-time physical activity and vitamin D status, as well as whether the observed association varies with place of activity (outdoor or indoor), type of activity (vigorous or moderate), age, race/ethnicity, and time of year.
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.
Introduction
Increasing evidence suggests that low vitamin D status is a risk factor for a range of diseases, including bone disease, infection, cancer, diabetes, and cardiovascular disease. A recent meta-analysis of 18 randomized trials including more than 57,000 participants demonstrated a significant reduction in all-cause mortality among older individuals assigned to vitamin D supplements. Sun exposure is the primary determinant of vitamin D status, but age and the degree of skin pigmentation are known to modify the effect of the sun on vitamin D synthesis.
Since the late 1970s, researchers have noted that body levels of vitamin D, as measured by serum 25-hydroxyvitamin D, decline with age. This decline is due partly to a decreased capacity by the epidermis of the elderly to photosynthesize previtamin D, as compared with younger subjects, but the decline also may be due to decreased sun exposure because sun tanning and sun burning decrease with age.
Racial/ethnic variations in vitamin D status also occur, with lower levels observed in non-Hispanic Blacks and Mexican Americans compared with non-Hispanic Whites. Vitamin D insufficiency (serum 25-hydroxyvitamin D, <50 nmol/liter) is much more common among non-Hispanic Blacks (in winter ranging from 53 percent to 76 percent across the main age-sex subgroups) than in Mexican Americans (18-50 percent) and non-Hispanic Whites (8-33 percent). Studies of vitamin D photosynthesis have shown that non-Whites have a similar capacity to synthesize vitamin D, but they require longer exposure to sunlight to achieve a similar vitamin D response because of their increased skin pigmentation.
Outdoor activities increase body vitamin D levels through sun-induced synthesis of vitamin D. Previous studies have shown a positive association between physical activity, in general, and vitamin D status. Blood levels of 25-hydroxyvitamin D have been observed to be higher in weightlifters and track athletes than matched sedentary controls in some studies but not all. The cited studies had small sample sizes (n < 60) that may have decreased power to detect an association between physical activity and 25-hydroxyvitamin D.
Few epidemiologic studies have examined the relation between leisure-time physical activity and vitamin D status in the general population. In the early 1990s, a cross-sectional survey of middle-aged men in New Zealand found that men who engaged in weekly leisure-time aerobic activities (indoor and outdoor combined) had significantly increased plasma levels of 25-hydroxyvitamin D compared with inactive men after adjustment for weekly hours of sunshine exposure, especially in winter. In a healthy workforce sample, also in New Zealand, the mean level of serum 25-hydroxyvitamin D3, the vitamin D metabolite formed mainly from sun exposure and which comprises the major portion of body vitamin D, was higher in people engaging in vigorous (aerobic) leisure physical activities compared with those who were inactive, after adjustment for age, sex, ethnicity, and time of year; moreover, serum 25-hydroxyvitamin D3 was 11-13 nmol/liter higher in those who participated in outdoor versus indoor activities. Recent reports have confirmed these earlier findings. Analyses of male US health professionals showed that participants in the highest quintile of leisure-time physical activity had a 13.5 nmol/liter higher level of plasma 25-hydroxyvitamin D than those in the lowest activity quintile. A cross-sectional survey in Florida found that osteoporosis patients who reported participating in outdoor exercise were 47 percent less likely to have hypovitaminosis D (25-hydroxyvitamin D, ≤30 ng/ml or 75 nmol/liter) than were nonoutdoor exercisers. Finally, Dutch studies of older people living in the community have observed a positive association between the level of physical activity and serum 25-hydroxyvitamin D and reported that serum 25-hydroxyvitamin D increased by 1.8 nmol/liter for each hour per day of outdoor activity.
The Third National Health and Nutrition Examination Survey (NHANES III) involved a representative sample of the US civilian population, who were interviewed during 1988-1994. With serum 25-hydroxyvitamin D measurements from over 19,000 participants, NHANES III offers a unique opportunity to examine the association between leisure-time physical activity and vitamin D status, as well as whether the observed association varies with place of activity (outdoor or indoor), type of activity (vigorous or moderate), age, race/ethnicity, and time of year.
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