Science can be a fickle thing sometimes. Research interests wax and wane and priorities shift as a consequence of trends, resources and funding. Take for example the science behind vitamins and minerals and the shifting sands of research interest. At one time, vitamin C was a focus (partially as a result of the interest of Nobel Prize winner Linus Pauling). Then it was the B-vitamins. Nowadays, vitamin D basks in the research sunshine, implicated in just about everything from cancer  to diabetes . Quite a way from the old fashioned connection with rickets  I’m sure you’ll agree although still relevant to the recent reports of an upsurge in cases of the “English disease” both in  and outside of England’s borders .
Interest in a connection between vitamin D and more behaviorally defined conditions has likewise increased in recent years. Schizophrenia has been correlated with low vitamin D levels  as has the potential risk of schizophrenia  and related conditions of mental illness  in particular groups. Certain types of depression  have also been correlated to vitamin D status as the list of associated conditions ever grows
Autism has not escaped the vitamin D research net as exemplified by the quite recent suggestion of low levels of 25-hydroxy vitamin D (the active form of vitamin D) present in cases of autism . It should be noted that this is not the first time that vitamin D inadequacy or deficiency has been cited in the autism research literature [11,12] as questions about risk factors such as migration  and the implications of such a deficiency start to be asked  including a possible link to a pet topic of mine, gut hyperpermeability .
Several possibilities arise to potentially explain why vitamin D is deficient in some cases of autism. Given the link between sun exposure and production of vitamin D, one could argue that such deficiency may arise at least in part, as a consequence of not getting enough sunshine whether through inactivity or as a result of the message about sun safety and covering up that we are all exposed to these days. Given that physical activity levels in autism don’t necessarily point to any major differences compared with peers  alongside no significant difference in sun exposure times between autism and control groups as noted in the recent trial , one has to look elsewhere for a possible explanation. Questions remain about whether dietary differences might account for vitamin D deficiency, or whether biochemical processes involved in the synthesis of vitamin D may be aberrant in cases of autism.
One of course has to remember that studies of association finding issues with vitamin D related to autism (or anything else) are just that: studies of association. Whilst entertaining the possibility that low levels of vitamin D might show some “causality” to cases of autism, one has to accept that at the current time on the basis of the evidence at hand, any relationship may be purely coincidental or indeed reflective of comorbidity which has seemingly little to do with autism. With no medical advice given or intended, trials of vitamin D supplementation may offer some supporting evidence for a more direct role for vitamin D and autism, assuming that is, appropriate functioning of the biological metabolism of the vitamin and its receptors.
 Ingraham BA. et al. Molecular basis of the potential of vitamin D to prevent cancer. Current Medical Research & Opinion. 2008; 24: 139-149.
 Mitri J. et al. Vitamin D and type 2 diabetes: a systematic review. European Journal of Clinical Nutrition. 2011; 65: 1005-1015.
 Wagner CL. et al. Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. Pediatrics. 2008; 122: 1142-1152.
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 Bandini LG. et al. Comparison of physical activity between children with autism spectrum disorders and typically developing children. Autism. 2012. (in press).