Vitamin D and Cardiovascular Disease: Jury Is Still Out

Fat-soluble vitamin D seems to be the vitamin we talk about most these days. In particular, researchers, clinicians, and pharmacists all have an opinion about whether vitamin D supplementation is necessary or wise.

Researchers from Emory University School of Medicine in Atlanta have published a paper in the Journal of the American College of Cardiology. In it, they discuss the controversy surrounding vitamin D and its potential associations with cardiovascular disease (CVD).

The authors indicated that serum levels of vitamin 25-0H D below 20 ng/mL are inadequate to maintain bone health, and are therefore diagnostic of deficiency. However, they noted that researchers and clinicians have not yet reached a consensus about the optimal level to maintain overall health. Some experts indicate that levels between 20 ng/mL and 29 ng/mL are indicative of insufficiency.

Hepatic mitochondria and their associated microsomal enzymes metabolize vitamin D, whether the patient obtains it from food sources or supplements. When patients consume too much vitamin D₂ or vitamin D₃, this process is completely unregulated and patients' vitamin D levels will rise proportionally to their intake. On the other hand, cutaneous synthesis from sun exposure allows patients levels to reach a preset point, and after that, additional sun exposure will not increase vitamin D levels.

In terms of cardiovascular disease, there seems to be some association between vitamin D deficiency and hypertension, insulin resistance, type 2 diabetes, and dyslipidemia in patients who are vitamin D-deficient. Vitamin D deficiency is also considered an independent risk factor for CVD development.

According to the study, up to 50% of all adults worldwide are vitamin D-deficient or vitamin D-insufficient. The authors reviewed potential mechanisms by which vitamin D might influence development of CVD and evidence supporting vitamin D deficiency's relationship to comorbid conditions. They proposed that CVD may cause low vitamin D levels rather than being caused by low levels.

Sometime in 2018, the VITamin D and Omega-three triAL (VITAL) will conclude its first part and provide some evidence to indicate whether vitamin D supplementation at a level of 2000 IU/day with or without omega-3 fatty acids has specific CVD effects. This large study has enrolled about 25,000 healthy, middle-aged American adults. It has also been structured to gauge long-term effects. VITAL is expected to augment the wealth of information that we possess concerning vitamin D supplementation for bone health.

Additionally, the authors stressed that patients whose vitamin D levels are lower than 19 ng/mL should be treated with 50,000 IU/week of either vitamin D₂ or D₃ for 8 weeks followed by a maintenance dose between 1500 and 2000 IU daily.

They also remind readers that patients with end-stage renal and or hepatic diseases often develop hypocalcemia related to vitamin D activation impairment and need supplementation. Patients with secondary hyperparathyroidism or hypoparathyroidism also need vitamin D supplementation.

Healthy individuals will benefit by casual sunlight exposure (10 to 15 minutes every day) and including fatty fish or fish oils in their diets in addition to vitamin D-enhanced food products. Most diets contain an insufficient quantity of vitamin D₂ or D₃, which means that patients can benefit from vitamin D supplementation.

Reference

Al Mheid I, Quyyumi AA. Vitamin D and cardiovascular disease: controversy unresolved. J Am Coll Cardiol. 2017 Jul 4;70(1):89-100. doi: 10.1016/j.jacc.2017.05.031.