Vitamin D Status in Cats with Cardiomyopathy

In the literature

Ware WA, Freeman LM, Rush JE, Ward JL, Makowski AJ, Zhang M. Vitamin D status in cats with cardiomyopathy. J Vet Intern Med. 2020;34(4):1389-1398.

The Research …

Vitamin D is a fat-soluble vitamin. Severe vitamin D deficiency can cause rickets or osteomalacia, and even subclinical vitamin D deficiency can have detrimental effects.¹ In humans with cardiovascular disease, low vitamin D levels have been associated with progressive disease and poorer outcomes. Vitamin D levels in cats, particularly cats with cardiomyopathy, have not been well-studied.

The biologically active form of vitamin D is calcitriol (1, 25[OH]₂D₃). Dogs and cats must obtain precursors for vitamin D from their diet, as they cannot convert precursors in the skin to vitamin D with exposure to ultraviolet light.² Dietary precursors include cholecalciferol (25[OH]D₃; vitamin D₃) from animal food sources and ergocalciferol (25[OH]D₂; vitamin D₂) from plant-based sources. Cats also form a C3 epimer of vitamin D₃ (3-epi).³ This epimer has also been observed in humans, rats, and dogs but at very low levels.^2,4,5 Assessment of vitamin D status is generally based on serum levels of precursors, as calcitriol is less stable in circulation.

The primary goal of this cross-sectional observational study was to determine if vitamin D status is lower in cats with cardiomyopathy.

As a secondary goal, this study also evaluated whether vitamin D levels were associated with certain patient variables or severity of cardiomyopathy.

Clinical cases of cats with echocardiographic evidence of left atrial enlargement secondary to any type of cardiomyopathy (n = 44), including hypertrophic, restrictive, dilated, or unclassified/nonspecific, were recruited. A group of normal cats (n = 56) was also enrolled for comparison. All cats had to be primarily fed a commercial cat food, and a detailed dietary history was obtained for each cat. A venous blood sample was collected from each cat and submitted for measurement of 25(OH)D₂, 25(OH)D₃, and 3-epi. Only 25(OH)D₃ and 3-epi levels were included in the final analysis; 25(OH)D₂ was below detectable limits for both groups.

Increasing age was significantly associated with decreasing levels of both 25(OH)D₃ and summation vitamin D levels (ie, 25[OH]D₃ combined with 3-epi), whereas left ventricular fractional shortening and survival times were positively correlated with 25(OH)D₃ and summation vitamin D levels. Cats with cardiomyopathy had significantly lower summation vitamin D levels. The cardiomyopathy group had higher estimated levels of dietary vitamin D intake, but no correlation between intake and serum levels of 25(OH)D₃, 3-epi, or summation vitamin D levels was noted.

Overall, older cats had lower levels of vitamin D. In addition, summation vitamin D levels were lower in cats with cardiomyopathy as compared with normal cats. Both 25(OH)D₃ and summation vitamin D levels were positively associated with fractional shortening and survival time. Of note, there were substantial levels of the epi-3 metabolite detected in both groups of cats, suggesting this metabolite is important in this species, and summation vitamin D may be a potentially more useful clinical index for assessment of vitamin D status in cats as compared with 25(OH)D₃ alone.

… The Takeaways

Key pearls to put into practice:

• Both vitamin D₃ and its C3 epimer (3-epi) can be measured in cats, and levels of 3-epi appear to be higher in cats as compared with humans and dogs.

• Age appears to have a significant effect on vitamin D levels in cats, and lower levels may be noted in older cats, regardless of cardiomyopathy status.

• Vitamin D₃ and the summation of vitamin D₃ and 3-epi appear to be positively correlated with survival; lower levels may be noted in cats with more advanced cardiomyopathy and congestive heart failure.