Even though important factors for vitamin D synthesis were similar, there was severe vitamin D deficiency in patients presenting with an acute episode, significantly different from those in remission. Is vitamin D deficiency the result or the cause of an acute episode? Our results contribute to the idea that vitamin D deficiency and schizophrenia may have interactions with an unknown pathway. Present data points out a possible influence at a genomic level. Future trials may investigate this association with longer follow up. We recommend that, serum vitamin D levels should be measured in patients with schizophrenia especially in long term care. Appropriate further treatment with add-on vitamin D supplements and diets that are rich in vitamin D should be considered.

Patients in an acute episode had significantly lower vitamin D levels compared to patients in remission and to healthy controls (in terms of median values respectively, 7.18, 15.03, 15.02, p < 0.001). We observed negative and moderate correlations between vitamin D levels and CGI scores ( r = −0.624, p < 0.001), vitamin D levels and PANNS scores ( r = −0.508, p < 0.001). There were no significant differences between groups in terms of serum P, Ca and PTH levels ( p = 0.099, p = 0.943, p = 0.762). We could not detect any significant impact of weekly duration of sun exposure, skin color, ethnicity or nutrition on total vitamin D levels.

41 patients with schizophrenia in remission, 40 patients with schizophrenia those in an acute episode and 40 age- and sex -matched controls with no major psychopatology were recruited in this study. Positive and Negative Syndrome Scale (PANSS) and the Clinical Global Impression – Severety scale (CGI-S) were used to evaluate disease activity. A demographic data form that included entries on age, gender, ethnicity, weight, skin color, daily duration of sun exposure and nutritional assessment were used. Blood samples were taken from all patients and controls. Total vitamin D (D2+D3), calcium, phosphor, parathyroid hormone values were measured.

Vitamin D deficiency is one of the implicated factors in ethio-pathogenesis of schizophrenia. Low serum vitamin D levels have been reported in many schizophrenia studies. However, the question is still not answered: Is there a correlation between disease activity and serum vitamin D levels? This is the first study evaluating the relationship between serum total vitamin D levels and disease activity, by comparing total vitamin D levels in two schizophrenia groups abruptly different in terms of disease activity.

Material and methods Participants This study was performed at the Department of Psychiatry of Ankara Numune Training and Research Hospital, Turkey. We recruited 41 patients with schizophrenia in remission who came to the outpatient clinic between June and November 2013, and 40 patients with schizophrenia in an acute episode, hospitalized in our inpatient clinic between June and November 2013. Forty age- and sex-matched controls with no major psychopathology were recruited from the Family Medicine Clinic at Ankara Numune Training and Research Hospital. Inclusion criteria were a diagnosis of schizophrenia according to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, Text Revision (DSM-IV-TR), and 18–65 years of age. An additional inclusion criterion for outpatients was being in remission for at least 6 months according to Andreasen criteria [Andreasen et al. 2005]. Patients in an acute episode were included if they had a score of 4 or more (moderate or severe) on the Positive and Negative Syndrome Scale (PANSS) target item either for delusions (P1) or hallucinations (P3) and a score of 4 or more on the Clinical Global Impression (CGI) scale. Individuals were excluded if they had a diagnosis of alcohol or substance dependence, organic mental disorder or learning disability, or a metabolic disease that may affect serum vitamin D concentrations. Design and procedure We did a case–control study to examine the association between disease activity and serum total vitamin D levels in patients with schizophrenia. The sample consisted of three groups: patients with schizophrenia in remission, those in an acute episode, and controls. Considering the seasonal fluctuation of vitamin D, patients were enrolled during the summer and fall of 2013. Trained physicians administered all the clinical assessments. The study received approval by the local ethics committee. Instruments All patients were given an informed consent form, the PANSS, the CGI – Severity scale (CGI-S) and a demographic data form that included entries on age, sex, ethnicity, occupation, marital status, weight, skin color, daily duration of sun exposure and nutritional assessment. Blood samples were taken from all patients and controls. PANSS and CGI scales We assessed the remission status using the PANSS and the CGI-S. The scales were administered on the same day that the blood sample was drawn. Blood samples and laboratory analysis With informed consent of patients, 10 cm3 peripheral venous blood samples were taken, placed in gel-containing tubes and centrifuged at 4000 rpm for 10 min to analyze the separated serum. Hemolysed and icteric serums were not used in this study. Calcium and phosphorus values were evaluated photometrically in a Roche P800 autoanalyzer (Roche Diagnostics Turkey A.S, Ankara) using original commercial kits. Parathyroid hormone (PTH) and total vitamin D (25-hydroxyvitamin D) values were measured by elecroluminescence with a Roche Cobas e-601. This assay is used as an aid in the assessment of vitamin D sufficiency. The electrochemiluminescence binding assay is intended for use on Elecsys (Elecsys 2010 Roche Immunoassay Analyzer, Turkey) and Cobas e immunoassay analyzers. A sufficient level of total vitamin D was considered to be 20–100 ng/ml; an insufficient level, 10–20 ng/ml; a deficient level, less than 10 ng/ml [Holick, 2007]. Statistical analysis Statistical Package for the Social Sciences (SPSS) 20.0 was used for the analysis. In the statistical review of the results, the Kolmogorov–Smirnov test was used to determine whether the parameters were normally distributed. While descriptive statistics for continuous variables were shown as mean ± standard deviation, categorical variables were expressed as number of cases (n) and %. The Student t test was used for the comparison of the two groups, one-way analysis of variance (ANOVA) was used for the comparison of the three groups for parametric variables. The Mann–Whitney U test and Kruskal–Wallis test were used for nonparametric variables. The Pearson correlation test was used to determine the association between the continuous parametric variables, and the Spearman correlation test was used to determine the association between the continuous nonparametric variables. The results were evaluated for a significance level of p < 0.05.

Results Patients with schizophrenia in acute episode Overall, 40 patients with schizophrenia in an acute episode were enrolled. Their average age was 38.08 ± 11.26 years (range 20–60 years). There were 20 men (50%) and 20 women (50%). The median of schizophrenia disease duration was 5.5 years (1–15 years, as 25–75%). The average PANSS score was 115.35 ± 20.37; positive psychotic symptoms scored 31.35 ± 7.91, negative psychotic symptoms scored 27.22 ± 10.00 and general psychopathology scored 56.77 ± 10.91 (Table 1). Table 1. Baseline characteristics of study sample by disease activity in three groups (n=121). View larger version Patients with schizophrenia in remission For comparison, we enrolled 41 patients with schizophrenia in remission. Their average age was 38.85 ± 10.64 years (range 19–66 years). There were 27 men (65.9 %) and 14 women (34.1%). The median of schizophrenia disease duration was 10 years (7.5–20 years, as 25–75%). The average PANSS score was 53.58 ± 12.09; positive psychotic symptoms scored 11.48 ± 3.20, negative symptoms scored 17.0 ± 4.88 and general psychopathology scored 25.09 ± 7.88. Healthy controls For a second comparison we recruited 40 healthy controls, 19 men (47.5%) and 21 women (52.5%), and their mean age was 41.85 ± 13.42 years (range 17–58 years). Serum total vitamin D levels Patients with schizophrenia in an acute psychotic episode had significantly lower total vitamin D levels compared with patients with schizophrenia in remission and healthy controls (in terms of median values: 7.18, 15.03, 15.02, respectively, p < 0.001). One-way ANOVA showed significant differences in vitamin D levels of patients with schizophrenia and healthy controls. Post hoc analysis revealed that patients with schizophrenia in acute episode had lower vitamin D levels than either patients with schizophrenia in remission or control subjects. There was no significant difference between total vitamin D levels in the remission group compared with healthy controls. When patients were grouped according to total vitamin D ranges (deficient < 10 ng/ml, insufficient 10–20 ng/ml, sufficient 20–100 ng/ml), the acute-episode group comprised a greater proportion of all patients who were vitamin D deficient compared with those who were vitamin D insufficient: 26/40 (60%) versus 12/40 (30%), respectively (Table 2). Table 2. Vitamin D deficiency distribution according to groups. View larger version We also evaluated serum phosphorus (P), calcium (Ca) and PTH levels in order to discriminate between other possible biological effects on total vitamin D serum concentrations. There were no significant differences between groups in terms of serum P, Ca and PTH levels (p = 0.099, p = 0.943, p = 0.762) (Table 3). Table 3. Serum vitamin D, PTH, Ca and P levels according to groups. View larger version As presented in Table 1, we could not detect any significant impact of weekly duration of sun exposure, skin color and ethnicity, or nutrition on total vitamin D levels. Total vitamin D levels and disease activity We observed negative and moderate correlations between total vitamin D levels and CGI scores (r = −0.624, p < 0.001), total vitamin D levels and PANNS scores (r = −0.508, p < 0.001) and total vitamin D levels and negative symptom scores (r = −0.508, p < 0.001). Positive symptom scores and general psychopathology scores were also correlated with total vitamin D levels negatively, but mildly (r = − 0.373, p < 0.001; r = –0.443, p < 0.001) (Table 4). Table 4. Association between serum total vitamin D levels and clinical evaluation. View larger version The level of total vitamin D did not correlate with disease duration and number of hospitalizations. When we controlled for the effects of other variables (age, sex, disease duration, sun exposure, nutrition, skin color), we also detected a negative and moderate correlation between total vitamin D levels and CGI scores (r = −0.566, p < 0.001) and total vitamin D levels and PANNS scores (r = −0.500, p < 0.001).

Discussion To our knowledge, this is the first report of a significant association between vitamin D deficiency and disease activity in adults with schizophrenia. Our results indicate that many of the patients with schizophrenia have vitamin D deficiency, similar to other studies [Belvederi Murri et al. 2013; Itzhaky et al. 2012; Jamilian et al. 2013]. Our results also indicate that patients in an acute episode have lower serum concentrations of total vitamin D compared with patients in remission, and there is an inverse association between total vitamin D concentrations and disease activity based on PANSS and CGI-S scores. This finding remained after evaluating the impact of various factors such as sex, ethnicity, skin color, self-reported sun exposure and diet composition. Current data show that there are three adult studies and one adolescent study examining the association between serum concentrations of vitamin D and severity of psychotic symptoms. A cross-sectional study reported negative correlations between vitamin D concentrations and physical energy, psychomotor activity and somatic complaints [Berg et al. 2010], whereas Itzhaky and colleagues reported no correlation between vitamin D concentrations and PANSS scores [Itzhaky et al. 2012]. The other study examining this association was a case–control study from the UK [Crews et al. 2013]. This study reported that patients with first-episode psychosis have significantly lower concentrations of vitamin D, similar to our findings, but did not find an association between vitamin D concentrations and the severity of illness, in contrast to our findings. Herein, it may be useful to review the sampling of the other studies. If the sample consisted of similar patient groups, such as all in remission or all in acute episode/hospitalized, this could cause a similarity in disease activity. In our study, to precisely determine the association between disease activity and vitamin D levels, we designed two patient groups strictly different in their disease activity. However, in the aforementioned study all of the patients were in acute episodes. This is also the first study to report total serum vitamin D concentrations of patients with schizophrenia in Turkey. Our findings show that both patients with schizophrenia and the control group have significantly lower total serum vitamin D concentrations. In fact, Turkey is located at appropriate latitudes (36° 42’ N) for the synthesis of vitamin D [Amato et al. 2010] and thus higher levels of total vitamin D would be expected. However, a study from Israel (31° 30’ N), which is located at similar latitudes to Turkey, also reported low serum vitamin D concentrations in patients with schizophrenia. Our results show that patients with schizophrenia in the remission group and control group have similar total serum vitamin D concentrations. For the control group, we recruited patients from the Family Medicine Clinic, and these patients had mild health problems, so the control group may not reflect the whole Turkish population. When it comes to patients with schizophrenia, especially in the acute episode group, there was severe vitamin D deficiency even though important factors for vitamin D synthesis such as sex, ethnicity, skin color, daily exposure to sunlight and nutrition were similar in both groups. This result may suggest the existence of an unknown interaction between disease activity and serum concentrations of total vitamin D. Why does the total vitamin D level fall during an acute period of disease? Is vitamin D deficiency the result or the cause of an acute episode? For the answer, we may look at the possible genetic interactions between schizophrenia and vitamin D, as well as the neuroprotective effects of vitamin D. Indeed, research from Italy published in 2010 reported a significant overlap of 70 genes between schizophrenia and vitamin D related genes (an overlapping gene is a gene whose expressible nucleotide sequence partially overlaps with the expressible nucleotide sequence of another gene; in this way, a nucleotide sequence may make a contribution to the function of one or more gene products). This analysis provides the first hint, at a genomic level, of the existence of a relationship between schizophrenia and vitamin D related genes. So, our findings contribute to the idea that vitamin D deficiency and schizophrenia may have been influenced at a genomic level.

Limitations of this study For the understanding of whether vitamin D deficiency is a state marker or trait marker for schizophrenia, follow up should be conducted after the treatment of acute episodes. Because this is a case–control study, it is not possible to understand if the vitamin D deficiency is a cause or result of schizophrenia. Future cohort studies may investigate the association with longer follow up.

Clinical therapeutic implications for schizophrenia therapeutics and conclusions Vitamin D deficiency is highly prevalent in patients with schizophrenia, especially those in acute episodes. Low serum vitamin D concentrations may have an effect in the pathogenesis of schizophrenia, or schizophrenia and vitamin D deficiency may have a genetic cooccurrence. Our findings suggest routine testing of vitamin D concentrations in patients with schizophrenia. Given that vitamin D is neuroprotective, adequate serum vitamin D concentrations may be effective to prevent new acute episodes in the course of schizophrenia. Nevertheless, it is not known what dose of vitamin D is neuroprotective. So, future trials of vitamin D supplementation are needed to focus on dosing and tolerability in patients with schizophrenia. However, we recommended that patients with schizophrenia who are in long-term care in rehabilitation psychiatric units should be assessed with regard to their vitamin D levels. According to their vitamin D levels, these patients should have appropriate exposure to sunlight, activity and dietary adjustments to normalize vitamin D levels. Vitamin D containing foods are very few in nature. Fatty fish (such as tuna, salmon and mackerel) and fish liver oils are the best sources [Ross et al. 2011]. Beef liver, cheese, egg yolks and mushrooms are other vitamin D sources [Cranney et al. 2007]. Fortified foods such as milk and breakfast cereals often contain added vitamin D, as do some brands of orange juice, yogurt, margarine and other food products. So diets that are rich in vitamin D can be given to these patients. We believe that these interventions should be maintained during patients’ stay in any such facilities where exposure to sunlight is limited. Appropriate further treatment with add-on vitamin D supplements should be considered based on patients’ physical and mental health using the guidelines for vitamin D supplementation.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Conflict of interest statement

The author declares that there is no conflict of interest.