Vitamin D status and seasonal variation in patients with schizophrenia

Introduction

Schizophrenia is a chronic and severe psychiatric disorder that affects approximately 1% of the global population. It is characterized by disturbances in thought processes, perceptions, emotional responsiveness, and social interactions. Although its etiology is multifactorialcomprising genetic, neurobiological, and environmental components-recent research has increasingly focused on the role of nutritional and hormonal factors, including vitamin D, in its pathophysiology [1][2][3] . Vitamin D, a fat-soluble secosteroid hormone, is synthesized in the skin upon exposure to ultraviolet B (UVB) radiation from sunlight and is also obtained in limited amounts from dietary sources. It plays a vital role in calcium homeostasis, immune regulation, and neuronal development. The presence of vitamin D receptors in brain regions involved in mood regulation and cognition (such as the hippocampus and prefrontal cortex) suggests a plausible link between vitamin D status and psychiatric disorders, including schizophrenia [46] . Several studies have reported that individuals with schizophrenia often exhibit lower levels of serum 25-hydroxyvitamin D [25(OH)D], the major circulating form of vitamin D. Moreover, because vitamin D synthesis is strongly influenced by seasonal sunlight exposure, there may be significant fluctuations in vitamin D status depending on the time of year, with lower levels commonly observed during winter months [7][8][9][10] . Understanding the seasonal variation in vitamin D levels among patients with schizophrenia is crucial, as it may contribute to the exacerbation of symptoms or impact treatment response. Identifying such a relationship can help in optimizing patient care through preventive strategies like vitamin D supplementation or sunlight exposure recommendations [11][12][13] . This study aims to investigate the status of vitamin D and its seasonal variation in patients with schizophrenia attending a tertiary care hospital and explore its association with clinical symptom severity.

Materials and Methods

A cross-sectional observational study was conducted over 12 months at a tertiary care hospital. This study was conducted at the department of Biochemistry, Madha Medical College and Research Institute, Kundrathur Main Road, Kovur, Chennai, Tamil Nadu, India from March 2017 to February 2018. 60 patients diagnosed with schizophrenia (based on ICD-10 criteria) over a period of one year. Patients were stratified into two seasonal groups based on the time of presentation: summer (April-September) and winter (October-March). Serum 25(OH)D levels were measured using chemiluminescent immunoassay. Clinical severity was assessed using the Positive and Negative Syndrome Scale (PANSS). Patients with comorbid metabolic or endocrine disorders were excluded.

Inclusion Criteria

Results

The study included 60 patients with schizophrenia, of whom 32 (53.3%) were assessed during the winter season and 28 (46.7%) during the summer season. The findings are presented below in five tables with descriptions. Vitamin D levels were significantly lower in winter compared to summer (p< 0.01). Over 70% of patients evaluated in winter were deficient, compared to less than 40% in summer. Patients with vitamin D deficiency had significantly higher PANSS scores (indicating worse symptom severity) compared to those with sufficient levels (p< 0.01). There was a moderate negative correlation between vitamin D levels and PANSS scores, suggesting that lower vitamin D is associated with higher symptom severity. [14,15] . The significant seasonal variation seen in our cohort, where vitamin D deficiency was more prevalent during winter (71.9%) than summer (39.3%), supports the evidence that sunlight exposure directly influences serum vitamin D levels, which in turn may modulate mood and psychotic symptoms. This is supported by Kesby et al. (2011) who discussed the influence of vitamin D on neurotransmitter pathways and neuroplasticity, which are altered in schizophrenia [16,17] . Furthermore, the finding that vitamin D-deficient patients had higher PANSS scores is consistent with Schneider et al.

(2014), who reported an association between low vitamin D levels and more severe positive and negative symptoms in psychotic patients. This suggests that vitamin D might not only play a preventive role but could also influence the clinical course and symptom severity of schizophrenia [18,19] . The correlation observed (r = -0.45, p = 0.002) between vitamin D levels and PANSS score indicates that as vitamin D levels decrease, psychotic symptom severity increases. This finding highlights the potential role of vitamin D as an adjunctive therapeutic target in schizophrenia, especially in regions or populations with limited sunlight exposure. Gender distribution in deficiency was nearly equal, emphasizing that seasonal influence outweighs genderbased differences in this context. This adds to the findings by Lansdowne and Provost (1998), who emphasized that seasonal affective changes, including vitamin D fluctuations, can influence neuropsychiatric outcomes in both males and females [20,21] .

Despite these findings, the study has limitations: the sample size is modest, and the cross-sectional design limits causal inferences. Longitudinal and interventional studies are necessary to determine whether vitamin D supplementation could meaningfully reduce symptom severity or alter the disease trajectory in schizophrenia. In conclusion, our study reinforces the growing body of evidence suggesting a link between hypovitaminosis D and schizophrenia. Monitoring and correcting vitamin D deficiency, particularly during winter, may represent a simple, low-risk strategy to optimize outcomes in psychiatric patients, though clinical trials are needed for definitive guidance [22,23] .

Conclusion

This study highlights a significant association between Vitamin D deficiency and schizophrenia, with evident seasonal variations in serum Vitamin D levels among patients. The majority of schizophrenia patients demonstrated suboptimal Vitamin D status, particularly during the winter months. These findings underscore the potential role of Vitamin D in the pathophysiology and clinical management of schizophrenia. Routine screening and correction of Vitamin D levels, especially in high-risk seasons, could be beneficial in improving the overall health and potentially the psychiatric outcomes in these patients. Further longitudinal and interventional studies are warranted to establish causality and the therapeutic implications of Vitamin D supplementation in schizophrenia care.

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