A quote to begin: "The evidence suggested that high levels of vitamin D may be linked to reduced risk of schizophrenia with elevated CRP [C-reactive protein]."
That was the bottom line reported by Dao-min Zhu and colleagues  who measured plasma concentrations of CRP and 25-hydroxyvitamin D [25(OH)D] in 93 people with schizophrenia and "93 family-matched controls." Finding that: "Mean levels of CRP and 25(OH)D were 43.3% higher and 26.7% lower for patients compared to controls" and that "25(OH)D were inversely associated with CRP in the patients, but not in the controls" provided scope for the authors to conclude that there may be quite a bit more to see in this area.
I've covered both schizophrenia and vitamin D (see here) and schizophrenia and CRP (see here) before on this blog. The trends described by Zhu et al pretty much follow what quite a large bank of research has indicated insofar as reduced vitamin D levels and elevated CRP bearing in mind the potential plurality of the schizophrenias. I've not as yet tried to link the two concepts (vitamin D and CRP) together but have an idea of where science might want to go with this based on some of the peer-reviewed evidence. Oh, and at this point I'll drop in the results from Liefaard and colleagues ...
Gut hyperpermeability. As I've talked about before, the biological role of vitamin D has been stretched and stretched in recent years such that a deficiency/insufficiency of the stuff goes way beyond just impacting on bone health and the 'English disease'. The idea that excessive intestinal (gut) permeability (yes, leaky gut) might show some connection to vitamin D levels (see here) is gaining popularity in recent years. Papers such as the one from Assa and colleagues  add to an increasing volume of literature suggesting that there is more to see in this area. This work has also started to translate to humans as well as mice . Coupled to the idea that intestinal inflammation - a potential cause of gut barrier disruption - might also be a facet of some schizophrenia (see here) and I don't think I'm getting too ahead of myself in suggesting that there may be an 'association' here.
The science should be pretty easy to do to confirm/refute any relationship; adding measuring gut permeability to the protocol followed by Zhu et al and perhaps even supplementing with vitamin D and re-checking gut permeability and inflammatory marker levels as a result. Given also the links being established between autism and vitamin D deficiency/insufficiency (see here) and inflammation or markers of inflammation being a facet of some autism (see here), I dare say that science could explore that area too.
Music: John Lennon - Imagine.
 Zhu DM. et al. High levels of vitamin D in relation to reduced risk of schizophrenia with elevated C-reactive protein. Psychiatry Res. 2015 Jun 10. pii: S0165-1781(15)00338-8.
 Liefaard MC. et al. Vitamin D and C-Reactive Protein: A Mendelian Randomization Study. PLoS One. 2015 Jul 6;10(7):e0131740.
 Assa A. et al. Vitamin D deficiency promotes epithelial barrier dysfunction and intestinal inflammation. J Infect Dis. 2014 Oct 15;210(8):1296-305.
 Raftery T. et al. Effects of vitamin D supplementation on intestinal permeability, cathelicidin and disease markers in Crohn's disease: Results from a randomised double-blind placebo-controlled study. United European Gastroenterol J. 2015 Jun;3(3):294-302.
Zhu DM, Liu Y, Zhang AG, Chu ZX, Wu Q, Li H, Ge JF, Dong Y, & Zhu P (2015). High levels of vitamin D in relation to reduced risk of schizophrenia with elevated C-reactive protein. Psychiatry research PMID: 26106052