Trending Clinical Topic: Vitamin D

Ryan Syrek

Disclosures

June 10, 2022

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Experts have suggested that the interest in vitamin D supplementation is so strong that it is seemingly impervious to evidence. Nevertheless, research into the connection between the nutrient and various health conditions continues. Recent findings have examined links to diabetes, obesity, breast cancer, and COVID. Interest in those studies resulted in vitamin D once more becoming the top trending clinical topic of the week. Among the notable research was a new study reiterating an old finding (see Infographic below).

The new findings come from the prospective Diabetes Prevention with active Vitamin D (DPVD) trial of more than 1200 Japanese participants with impaired glucose tolerance. Data show that vitamin D supplementation also failed to improve the rate of regression to normoglycemia compared with placebo. In an accompanying editorial, Tatiana Christides, MD, PhD, writes that the new trial is "well conducted, with rigorously defined and tested diagnostic criteria, and of sufficient duration, but it may have been underpowered to detect a small effect." She points to a recent meta-analysis of intervention trials, which found a significant 10% reduction in risk for type 2 diabetes with vitamin D supplementation. Christides adds that this was "a difference too small to be detected by the new trial...Although a 10% risk reduction is modest, it may be valuable at the population level and justifies further study."

A separate study, which has not yet been peer reviewed, found that 25-hydroxyvitamin D (25[OH]D) levels were inversely associated with glucagon and connecting peptide (C-peptide) levels in 4670 Chinese patients with type 2 diabetes and abdominal obesity. The lowest quartile had 25(OH)D levels ≤ 30.79 ng/mL; the highest quartile had levels ≥ 48.92 ng/mL. Among patients with type 2 diabetes without abdominal obesity, vitamin D levels were inversely and significantly associated with fasting plasma glucose, A1c, glucagon, and beta-cell function, after adjusting for multiple variables. Among patients with type 2 diabetes with abdominal obesity, vitamin D levels were inversely and significantly associated with A1c, glucagon, fasting insulin, fasting C-peptide, and insulin resistance. In patients with type 2 diabetes for a short time plus abdominal obesity, those with higher vitamin D levels had a lower ratio of glucagon to C-peptide; that is, they had a better homeostasis between islet alpha cells and beta cells than those with lower levels.

Another study involving vitamin D and weight, which also has yet to be peer-reviewed, found that men with overweight or obesity were significantly more likely to have inadequate 25(OH)D levels of < 20 ng/mL (50 nmol/L) independent of demographic and lifestyle factors. This was not seen among women. Compared with men who had normal weight, men with overweight were more likely to have vitamin D inadequacy (adjusted odds ratio [OR], 1.2; P = .03), as were men with obesity (adjusted OR, 1.4; P = .001), after adjusting for age, sex, place of residence, education, physical activity, alcohol consumption, and smoking.

Vitamin D deficiency was also recently tied to breast cancer risk in Hispanic and Black women. Vitamin D levels were measured from blood samples in 290 Black/African American women and 125 non-Black Hispanic/Latina women who developed breast cancer as well as 1084 Black/African American women and 461 Hispanic/Latina women who did not develop breast cancer. Over an average follow-up of 9.2 years, women with sufficient circulating 25(OH)D levels (20 ng/mL) had a 21% lower breast cancer rate than women with concentrations below this cut point, although the result fell short of statistical significance (hazard ratio [HR], 0.79; 95% CI, 0.61-1.02). The inverse association was strongest in Hispanic/Latina women (HR, 0.52; 95% CI, 0.29-0.93), with a weaker association seen in Black/African American women (HR, 0.89; 95% CI, 0.68-1.18; for heterogeneity = .13).

Earlier this year, vitamin D deficiency was also linked to increased likelihood of developing severe or critical COVID-19. In a study based on data from Israel's first two COVID waves, patients with vitamin D deficiency were 14 times more likely to have a severe or critical disease. The mortality rate among those with insufficient vitamin D levels was 25.6%, compared with 2.3% among those with adequate levels. These differences were consistent even after researchers controlled for age, gender, and history of chronic disease. Health officials in several countries have recommended vitamin D supplements during the pandemic.

From deficiency to supplementation, vitamin D research is always an incredibly popular area. With a wealth of recent research, it's no wonder that the topic has once again become the top trending clinical topic of the week.

Learn more about vitamin D deficiency.

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