Relation of Schizophrenia Prevalence to Latitude, Climate, Fish Consumption, Infant Mortality, and Skin Color: A Role for Prenatal Vitamin D Deficiency and Infections?

Abstract

Previous surveys found a large (>10-fold) variation in schizophrenia prevalence at different geographic sites and a tendency for prevalence to increase with latitude. We conducted meta-analyses of prevalence studies to investigate whether these findings pointed to underlying etiologic factors in schizophrenia or were the result of methodological artifacts or the confounding of sites' latitude with level of healthcare at those sites. We found that these patterns were still present after controlling for an index of healthcare--infant mortality--and focusing on 49 studies that used similar diagnostic and ascertainment methods. The tendencies for schizophrenia prevalence to increase with both latitude and colder climate were still large and significant and present on several continents. The increase in prevalence with latitude was greater for groups with low fish consumption, darker skin, and higher infant mortality--consistent with a role of prenatal vitamin D deficiency in schizophrenia. Previous research indicates that poor prenatal healthcare and nutrition increase risk for schizophrenia within the same region. These adverse conditions are more prevalent in developing countries concentrated near the equator, but schizophrenia prevalence is lowest at sites near the equator. This suggests that schizophrenia-producing environmental factors associated with higher latitude may be so powerful they overwhelm protective effects of better healthcare in industrialized countries. The observed patterns of correlations of risk factors with prevalence are consistent with an etiologic role for prenatal vitamin D deficiency and exposure to certain infectious diseases. Research to elucidate environmental factors that underlie variations in schizophrenia prevalence deserves high priority.

Vitamin D status in psychotic disorder patients and healthy controls – The influence of ethnic background

“…While we did not find any differences in S-25 OH D between adult patients with psychotic disorders and healthy controls, prospective studies have suggested vitamin D deficiency as a contributing factor to higher risk of developing psychotic disorders in dark skinned immigrants (McGrath, 1999;Dealberto, 2007;Kinney et al, 2009;McGrath, 2011). There are also associations between vitamin D deficiency and known risk factors for psychotic disorders like urban living, winter births (Kendell and Adams, 2002) and migration (Dealberto, 2007) An important strength of the current study is that the patient sample consists of both in-and outpatients, and thus can be seen as more representative of patients in general compared to samples recruited from inpatients' wards only.…”

Seafood Intake and Neurodevelopment: A Systematic Review

“…Among 20 articles identified and fully reviewed, 3 were further excluded because they did not meet the criteria for inclusion [11][12][13]. We also excluded a randomized control trial of a fish flour bread spread because of the different nature of the exposure compared to observational studies of seafood intake [14••].…”

Correlates of vitamin D in psychotic disorders: A comprehensive systematic review

“…The prevalence of psychotic disorders varies among different geographical locations, with increased rates in cold climates and high latitudes (Kinney et al, 2009). Furthermore, prevalence increases in individuals born in Winter/Spring months compared to Summer/Autumn babies (Kinney et al, 2009;Saha et al, 2005). These ecological findings suggest sun exposure and therefore vitamin D is a risk factor for psychotic disorders.…”