Introduction:
Vitamin D deficiency is an important health problem. Numerous studies reported a link between vitamin D deficiency and cancer as well as autoimmune and metabolic diseases. However, there are limited data on the association between vitamin D deficiency and metabolic dysfunction-associated steatotic liver disease (MASLD).

Aim of the research:
To assess the association between vitamin D deficiency and MASLD.

Material and methods:
This was a retrospective, single-centre study assessing the medical data of patients hospitalised at an internal medicine unit from January 2021 to December 2022. All patients were examined for vitamin D levels and the presence of MASLD.

Results:
The study included 446 patients, of whom 41% were diagnosed with MASLD. To determine if serum vitamin D levels can be used to differentiate between patients with and without MASLD, the area under the receiver operating characteristic curve was estimated, and the optimal cutoff value was identified by maximising the Youden index. The cutoff value based on the Youden index for vitamin D levels was 27.6 ng/ml. Vitamin D levels of 27.6 ng/ml or lower were reported in 79.8% of patients with MASLD (p = 0.0160). In a multivariable regression analysis, male sex, diabetes mellitus, obesity or overweight, and vitamin D levels of 27.6 ng/ml or lower predicted MASLD.

Conclusions:
The study confirmed that vitamin D deficiency is common among patients with MASLD. Vitamin D deficiency defined as vitamin D levels of 27.6 ng/ml or lower predicts MASLD. Vitamin D supplementation has the potential to become a therapeutic intervention aimed at reducing the risk of MASLD.