Sunlight, vitamin D, flu and schizophrenia.

This is my third post concerning the relationship between vitamin D deficiency and brain disorders.  Now I make the case that a major cause of schizophrenia is lack of sunlight or other source of vitamin D.

People born in seasons of little sunlight have higher schizophrenia risk.[1] 
Schizophrenia is also more common in dark-skinned migrants to cold climates, and increased rates of schizophrenia are observed in urban compared to rural settings.[2] 

Migrants to colder climates are 4.6 times more likely to develop schizophrenia than are natives.[3]

Another indication, proposed by Dr. William Grant,[4] is the correlation of influenza during women’s pregnancies to increased schizophrenia in their children.  Indeed, an investigation in Denmark demonstrated that flu during pregnancy predicted an 820% increased incidence of schizophrenia in children.[5]

That result could be due to brain damage resulting from the high fevers common to flu; it has been shown that there is a close relationship between fever in the pregnant mother and the risk of later schizophrenia in her children.[6]

But what does this have to do with vitamin D or sunlight?  Earlier I established that in summer, when vitamin D production is high, flu is nearly non-existent and that vitamin D supplementation in sufficiently high doses reduces the risk of flu to almost zero in the winter. 

Vitamin D stimulates the production of cathelicidins in the immune system. 

Cathelicidins destroy the cell walls of viruses, thereby keeping the flu at bay.  Therefore, vitamin D, by preventing flu, may help reduce schizophrenia risk provoked by fevers during pregnancy. 

Vitamin D, then, has a direct affect on the brain that reduces the risk of schizophrenia and an indirect effect by reducing the risk of flu. 

A further dramatic indication is that infant boys who are not supplemented with vitamin D are 12 times more likely to develop schizophrenia in later life compared to those who receive supplementation.[7]

 Vitamin D receptors are prevalent throughout the brain.  Those receptors are there for a purpose: proper brain development and function.  If we allow deficiency in our children, we do so at their peril. 

[1]McGrath, J.  et al.  Long-term trends in sunshine duration and its association with schizophrenia birth rates and age at first registration—data from Australia and the Netherlands.  Schizophr Res 2002;54:199-212.

[2] McGrath, J. et al.  Hypothesis: Is low prenatal vitamin D a risk-modifying factor for schizophrenia?  Schizophr Res 1999;40:173-77.
[3] McGrath, J. et al.  A systematic review of the incidence of schizophrenia: the distribution of rates and the influence of sex, urbanicity, migrant status and methodology.  BMC Med 2004;2:13-35.

    [4] Grant, W.  Personal communication with author, June, 2007.
    ^[5] Byrne, M.  Obstetric conditions and risk of first admission with schizophrenia: a Danish national register  based study.  Schizophr Res 2007;97:51-59.

[6] Edwards MJ. Hyperthermia in utero due to maternal influenza is an environmental risk factor for schizophrenia. Congenit Anom (Kyoto);2007;47:84-9.

[7] McGrath J, et al. Vitamin D supplementation during the first year of life and risk of schizophrenia: a Finnish birth cohort study. Schizophr Res. 2004;67:237-45.