The Possible Role of Vitamin D and Autoimmunity in the Etiology of Obsessive-Compulsive Disorder

Dear Editor,

Obsessive-compulsive disorder (OCD) is a common psychiatric disorder that is associated with autoimmune diseases.¹ Vitamin D deficiency could have an important role in both psychiatric disorders and autoimmune diseases.² We would like to report how thyroid autoantibody titers and OCD symptoms change as a result of vitamin D replacement in a patient with OCD.

A 35-year-old woman with OCD applied to our psychiatry clinic. The Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) score was 30. In the laboratory examination, there was anti-thyroglobulin antibody (anti-Tg: 235.3 IU/mL) and anti-thyroid peroxidase antibody (anti-TPO: 25 IU/mL) positivity, and 25-OH vitamin D deficiency (9.75 ng/mL). The thyroid function tests were normal, and it was stated that anti-TPO positivity can be found in the normal population without any clinical significance. Treatment with fluoxetine 20 mg/day and vitamin D 20 drops/day was started. At the end of 8 weeks, OCD symptoms decreased considerably. Meanwhile, serum vitamin D level (12 ng/mL) increased and anti-TPO (<9 IU/mL) and anti-Tg (<60 IU/mL) levels were detected in normal limits. The patient continued fluoxetine treatment but stopped taking vitamin D supplementation. She was in remission for 6 months (Y-BOCS score: <10 points).

After 6 months, the patient reported increased OCD symptoms for the last 2 weeks despite using fluoxetine treatment. In laboratory tests, serum vitamin D level (8.9 ng/mL) decreased, while anti-TPO level (34 IU/mL) and Y-BOCS score (23-point) increased. Considering that vitamin D deficiency might be responsible for the increase in clinical symptoms, vitamin D replacement was restarted and the patient was recommended to continue fluoxetine treatment. Three months later, while the patient’s vitamin D level (45.2 ng/mL) reached the normal range, both anti-TPO (0.8 IU/mL) and anti-Tg (<28 IU/mL) levels decreased, and OCD symptoms were in remission (Y-BOCS score: 9 points).

The researches emphasize that OCD symptoms are more common in patients with autoimmune thyroid diseases than in the normal population.³ Similarly, while vitamin D plays an important role in the biosynthesis of dopamine and catecholamines as a cofactor, lower vitamin D levels were found to be negatively correlated with OCD symptom severity.⁴ In the literature, there is only one case report that stated a relationship between OCD, autoimmune hypothyroidism, and low vitamin D levels in a pediatric patient.⁵

Vitamin D is supposed to have a neuroprotective function in the central nervous system by regulating neurotrophic factors, antioxidant molecules, neurotransmission, and neuroplasticity in the brain.^4,6  Therefore, vitamin D deficiency may contribute to the exacerbation of OCD symptoms by both impairing neurotransmitter synthesis and increasing inflammatory and oxidative load. Along similar lines, although the role of vitamin D in the mechanism of autoimmune diseases is not fully known, it is thought that vitamin D contributes to the pathophysiology of these autoimmune diseases by affecting its wide-range receptors on many innate and adaptive immune cells.⁷

When all these possible effects and mechanisms are considered together, it can be concluded that vitamin D deficiency may cause activation of concurrent thyroid autoimmunity and worsening in OCD clinic. Moreover, the triggering of thyroid autoimmunity may also contribute to the increase in OCD symptoms. In conclusion, serum vitamin D deficiency might be associated with OCD etiology directly or indirectly by affecting thyroid autoimmunity.

Funding Statement

The authors declare that this study has received no financial support.