Background To analyse the seasonal relationship of objectively measured physical activity with vitamin D status in older persons from Southern Germany (latitude: 48.4°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.