Time outdoors
hours / day
UV-B exposure, movement, and a SES-coded leisure habit.
Outdoor time is the hidden common cause of 25(OH)D and of 'having a life that looks healthy'. Desk-bound high earners in high latitudes can be rich and deficient; outdoor workers can be poorer and replete. That is why D is a terrible SES instrument.
Also called sun exposure, UV-B.
Connected relationships
MECHANISM+ INCREASES
Observational · High confidence
Time outdoors→25-hydroxyvitamin D
Higher Time outdoors increases 25-hydroxyvitamin D.
Skin makes 25(OH)D from UV-B; Samefors 2021 then showed that encouraging 40 Swedish nursing-home residents outdoors for two summer months raised median serum 25(OH)D from 42.5 to 53.5 nmol/L.