Objectively measured physical activity and vitamin D status in older people from Germany

Background To analyse the seasonal relationship of objectively measured physical activity with vitamin D status in older persons from Southern Germany (latitude: 48.4 degrees N). Methods Physical activity was assessed in 1193 community-dwelling individuals aged >= 65 years (58% men) over 1 week using a thigh-worn accelerometer. Furthermore, the 25-hydroxyvitamin D (25(OH) D) level was measured. Least-square means of 25(OH) D serum levels were calculated for quartiles of average daily walking duration stratified by season and adjusted for gender, age and body mass index. Participants with prescribed vitamin D supplements were excluded. Results Statistically significant linear associations between quartiles of walking duration with 25(OH) D serum levels were observed in all seasons but not in summer. Differences in 25(OH) D serum levels between the first and the last quartile were 3.42 ng/mL (p=0.002) in winter, 2.80 ng/mL (p=0.009) in spring, and 3.60 ng/mL (p<0.001) in the fall. The proportion of vitamin D insufficiency (<20 ng/mL) even in the highest quartile of walking duration was 45.3% in winter, 73.7% in spring, 17.4% in summer and 16.5% in the fall. Conclusions Although a positive dose-response relationship was seen between walking duration and the 25(OH) D serum level for most seasons, vitamin D insufficiency was still very prevalent even in high-active persons during all seasons.