Migration and Vitamin D in psychotic disorders – A cross sectional study of clinical and cognitive correlates

Abstract

Migration is a major environmental risk factor associated with schizophrenia and other psychotic disorders. Furthermore, people with migration background may have specific challenges due to their migration background or ethnic background influencing clinical correlates in established disease. An observed high prevalence of vitamin D deficiency in ethnic minorities in Northern European countries has generated hypotheses around the role of vitamin D in psychotic disorders. In this thesis we investigated the influence of migration, ethnicity and vitamin D levels in early phases of psychotic disorders and later in the course of illness. As vitamin D is found to have receptors widespread in the human brain and has been linked to the pathogenesis of core features in psychotic disorders, we wanted to explore the potential clinical relevance of vitamin D. Thus, investigating how vitamin D levels relate to specific symptom profiles and cognitive functioning. We conducted four cross-sectional studies in large clinical samples of patients with a DSM-IV diagnosis of a psychotic disorder from the public health care system in Norway. In two of the studies we also included healthy controls from the same catchment area as the patients. In the first study we investigated the associations between having migration background or ethnic minority status and duration of untreated psychosis. In the second, we explored the vitamin D levels in a first episode sample compared to a sample with longer duration of illness and a matched control group. In the third and fourth study we investigated the associations between vitamin D levels and symptom profiles in patients, and the associations between vitamin D deficiency and cognitive function in patients and in controls. Our main results are that migration after the age of six was significantly associated with prolonged duration of untreated psychosis while ethnic minority status only had a trend level significance for the same. Furthermore being an ethnic minority with ancestry from Asia, Africa or Latin-America, had a significant impact on vitamin D levels. Ethnic minorities had lower vitamin D levels than the majority population across groups; we found significantly lower levels both in first episode psychosis, in a sample of patients with a longer duration of illness, as well as in controls. However, we did not find any significant differences in vitamin D levels between patients and healthy controls, after controlling for ethnic minority status, as opposed to previous studies. Secondly we found that low vitamin D levels were associated with more severe negative and depressive symptomatology when controlling for a variety of potential confounding variables. Furthermore, a vitamin D level below a critical threshold, defined as vitamin D deficiency, was associated with cognitive functioning in terms of impaired processing speed and impaired verbal fluency, also after adjusting for patient versus control status and other potential confounders. In patients the associations between vitamin D deficiency and cognition were partly mediated by negative symptoms. The severity of the problems related to negative and depressive symptoms and cognitive impairments for patients with psychotic disorders indicate that these aspects are of clinical relevance. Negative symptoms and cognitive impairments have large impact on function and outcome both in the early phases of the disease and in a long term perspective and depressive symptoms are associated with reduced quality of life and impaired long term prognosis. Our studies demonstrated that migration and ethnic minority status provide specific challenges related to duration of untreated psychosis and vitamin D levels. The current findings in a health care based sample may suggest that further emphasis on the specific challenges of this population is needed. People experiencing migration and/or are ethnic minorities represent a vulnerable population both related to severity of severe mental illness related to prolonged duration of untreated psychosis, as well as vitamin D- derived somatic health problems. Our studies are cross-sectional and do not allow us to conclude about the directions of the associations. Our findings however provide support for initiating a randomized controlled trial to evaluate whether vitamin D substitution in individuals with low vitamin D levels has beneficial effect on either negative symptoms, cognitive impairments or depressive symptoms, as an adjuvant treatment strategy.