Vitamin D level is an activity or lifestyle marker, although this has been largely neglected in the medical literature, maybe except Gannage 2000, Hyppönen 2007, Sohl 2013 and Choi 213. A new paper by de Rui in PLoS now shows that
serum 25OHD levels were significantly higher in individuals who engaged in outdoor pastimes … compared to those who did not. In particular, subjects regularly practicing gardening or cycling had higher serum 25OHD levels than those who did not, whereas 25OHD levels differed little between subjects who did or did not undertake indoor activities.
While these are good news for older cyclists these are bad news for science as many of the papers linking vitamin D levels and disease acitivity are largely irrelevant. They are not describing biological effects of a vitamin D metabolite on disease severity but just link an activity marker with disease severity (which is somewhat boring). This is also my conclusion from the already famous Autier paper although the discussion this week shows that not everybody is being convinced yet.