Low serum 25-hydroxyvitamin D concentrations in chronic insomnia patients and the association with poor treatment outcome at 2months.

•Serum 25(OH)D concentrations in chronic insomnia patients were significantly lower than those of healthy control subjects.•Non-response patients had significantly lower 25(OH)D concentrations than response patients.•Vitamin D deficiency was independently associated with higher probability of treatment non-response at 2 months.•Measurement of serum 25(OH)D concentrations are probably useful for judging treatment outcomes of pharmacotherapy in chronic insomnia patients.