Background: Vitamin D is a major regulator of mineral bone metabolism. The lower vitamin D levels in patients with acute myocardial infarction (AMI) and the seasonal variation of vitamin D levels are proposed.

Aim: The evaluation of the seasonal relationship of 25(OH)D levels in patients with AMI and analysis of confounding factors (gender or diabetes mellitus) affecting the levels of vitamin D in AMI patients.

Methods: Fifty-nine consecutive patients with mean age 58 ± 9.4 years were admitted to the Department of Invasive Cardiology. Subjects had diagnosed uncomplicated myocardial infarction. Blood samples for analysis were collected on patient admission to the cardiac unit after heparin treatment. Samples for routine laboratory tests were immediately processed. For 25(OH)D, the 25-hydroxycholecalciferol test, which measures total vitamin D levels in serum (DRG Instruments GmbH, Marburg, Germany), was applied.

Results: Median serum 25(OH)D concentration in AMI patients was below the recommended optimal values 7.1 (2.3–13.3) ng/mL. Fifty-three (89.8%) patients had vitamin D deficiency (VDD) below 20 ng/mL, six (10.2%) patients had suboptimal 25(OH)D levels (between 20 ng/mL and 30 ng/mL), and no one had the recommended reference range. The seasonal effect of 25(OH)D variations among AMI patients was observed with the lowest levels in the beginning of the year (January–March) and the highest levels at the end of the year (September–December) (p = 0.007). Patients with normoglycaemia had significantly higher (9.2 [2.3–16.8] ng/mL) vitamin D levels compared to patients with impaired glucose tolerance (2.3 [2.3–3.9] ng/mL) or diabetes mellitus (8.5 [2.5–13.3] ng/mL) (p = 0.01).

Conclusions: A high prevalence of VDD in AMI patients has been confirmed. Supplementation of vitamin D in AMI patients with hyperglycaemia can bring greater benefits.