Vitamin D deficiency is relatively prevalent in most Western societies, particularly in breast-fed infants of African or Indian subcontinent origin due to a combination of reduced exposure to ultraviolet, maternal vitamin D deficiency, and genetic factors. Despite the relatively high prevalence of vitamin D deficiency, associated cardiomyopathy is rare, although it has been speculated that this may be due to under diagnosis.

Serum vitamin D levels are generally measured in the 1a-hydroxylated form, 25-hydroxyvitamin D [25(OH)D]. In most tissues and cells of the body this is then further hydroxlyated to the most active form, 1,25-dihydroxyvitamin D [1,25(OH)2D]. This has a number of direct and indirect effects on the myocardium, including promoting differentiation and proliferation of cardiomyocytes, regulation of myocardial contractility and intracellular calcium handling. In patients for whom deficiency results in important cardiomyopathy, presentation in infancy with signs of cardiac failure is typical. The disease course in this group is often fulminant and can be rapidly fatal without intensive cardiorespiratory support, including access to mechanical circulatory support and/or primary transplantation if required. However, in those that survive initial presentation, vitamin D deficient cardiomyopathy is one of the few readily treatable causes of DCM with an excellent long-term prognosis once appropriate support and nutritional supplementation are put in place. A list of other potentially reversible causes of DCM in the paediatric population is shown in Table 17.1.