Vitamin D deficiency has a high prevalence in Europe and the United States. In the past, studies on vitamin D have concentrated mostly on bone metabolism, however, according to recent studies, inadequate vitamin D has been related to major nonskeletal chronic illnesses, particularly cardiovascular disease. Vitamin D appears to lower the incidence of cardiovascular disease, and studies have shown that vitamin D deficiency is involved in the pathogenesis and worsening of heart diseases and heart failure. Based on recent studies, low levels of serum vitamin D seem to contribute to the pathogenesis and worsening of heart failure. The effects of vitamin D are derived from its binding to the vitamin D receptor (VDR), which is present in cardiac myocytes, but there are no studies on the cut-off value of 25-OH vitamin D that could protect against cardiac arrhythmias.

Vitamin D insufficiency has been identified as a marker of cardiovascular risk and accelerated atherosclerosis, according to large epidemiological studies. A lack of vitamin D causes systemic and vascular inflammation, which promotes atherogenesis, and vitamin D inhibits renin-angiotensin-aldosterone (RAA) activity both in animals and people. Suppression of renin synthesis and downregulation of RAA might explain the direct cardiac and vascular effects of vitamin D. In both normotensive and hypertensive individuals, clinical reports reveal an inverse dose-response association between plasma vitamin D concentration and renin activity. Low vitamin D levels have been linked to an increased risk of hypertension or high diastolic blood pressure, ischemic heart disease, myocardial infarction, and decreased coronary flow. Due to reduced sunlight exposure, difficult mobilization, and outdoor activity, as well as comorbidities, many patients with heart failure have low levels of vitamin D. It is also an independent risk factor for arterial hypertension and stroke, according to epidemiological studies. However, the VIDAL study showed that vitamin D supplementation was ineffective for primary prevention of CV events. Furthermore, there are numerous publications as well as meta-analyzes that connect atrial fibrillation (AF) with vitamin D deficiency. There are also reports of vitamin D deficiency leading to premature ventricular contractions (PVCs). The relationship between AF and vitamin D deficiency requires more experimental support with in vivo and in vitro research to explain the pathogenetic mechanisms.

This Special Issue aims to gather data related to cardiovascular diseases related to vitamin D deficiency. Special consideration will be given to cardiac arrhythmias induced by vitamin D deficiency. We invite authors to investigate the optimal level of vitamin D to protect against cardiac arrhythmias, based on clinical studies performed on patients with atrial or ventricular arrhythmias. We welcome both original research and review articles.

Potential topics include but are not limited to the following:

• Prevalence of vitamin D deficiency
• Seasonal variations of serum vitamin D
• Links between vitamin D deficiency and cardiac diseases
• Epidemiological studies of atrial fibrillation and vitamin D deficiency
• Mechanism of occurrence of atrial fibrillation in patients with vitamin D deficiency
• Meta-analysis of studies relating atrial fibrillation to vitamin D deficiency
• Vitamin D deficiency modifies heart rate variability
• QT interval modifications in patients with vitamin D deficiency
• Mechanisms of vitamin D deficiency aggravating heart failure and inducing arrhythmias
• Vitamin D deficiency and premature ventricular contractions
• Vitamin D deficiency and ventricular tachycardia (sustained and non-sustained)