Vitamin D deficiency is to be expected due to immune changes related to mental health problems

Stewart & Lewis¹ have shown that adolescent psychiatric in-patients typically have vitamin D deficiency and hypothesise that this may be due to reduced exposure to sunlight. This may well be true, but it is much more likely that the reduced vitamin D levels are due to changes in the immune system linked with psychiatric disorders. For example, it is now well known that depression is associated with inflammation² and that immune markers are typically raised. What is less well known is that vitamin D is a negative acute-phase reactant,³ which means that its levels drop in response to inflammation. Therefore, a low level may not indicate a deficiency, but rather the presence of inflammation. It would be interesting to reanalyse the data and see whether there are any links with particular diagnoses.