Relationship between daily time spent outdoors and serum 25-OH vitamin D levels. A scatterplot of the average hours per day spent outside vs. serum 25-OH vitamin D shows no correlation between the two. The median time spent outdoors was 3 hours/day (IQR 2–4).
Bose et al. Nutrition Journal 2013 12:81 doi:10.1186/1475-2891-12-81