Folate and cobalamin deficiency or impaired function due to genetic variants in key enzymes, have been associated with neuropsychiatric symptoms. The aim of this study was to compare folate and cobalamin status in patients admitted to an acute psychiatric unit to patients from primary health care, in order to reveal factors which may be important in the follow-up of patents with mental disorders.

Anonymous blood samples tested for folate, cobalamin, the metabolic marker total homocysteine (tHcy), creatinine and glomerular filtration rate, as well as age and gender in patients admitted to a psychiatric acute unit (n=981) and patients from primary health care (controls) (n=32201) were reviewed retrospectively.

Median serum folate was 18% lower and median serum cobalamin was 11% higher in patients with mental disorders compared to controls. Folate deficiency was associated with 54% higher median tHcy levels among patients with mental disorders compared to controls. The prevalence of folate deficiency was 31% and of cobalamin deficiency 6% in patients admitted to a psychiatric acute unit in a Norwegian hospital in 2024.

Folate, but not cobalamin deficiency, was prevalent in Norwegian patients with mental disorders. The higher tHcy levels in folate deficient patients with mental disorders indicate an impaired folate metabolism, which might be related to genetic factors, such as polymorphisms in the MTHFR gene. Ensuring a serum folate concentration above 15 nmol/L and a serum cobalamin above 250 pmol/L might improve symptoms in patients with mental disorders.