Trending Clinical Topic: Vitamin D

Ryan Syrek

Disclosures

November 12, 2021

Each week, we identify one top search term, speculate about what caused its popularity, and provide an infographic on a related condition. If you have thoughts about what's trending and why, share them with us on Twitter or Facebook.

From new studies on colorectal cancer and all-cause mortality (see Infographic below) to questions about vitamin D's role in combatting COVID-19, a wide variety of significant findings resulted in this week's top trending clinical topic.

A recent observational study found that women who consume higher levels of vitamin D — particularly from dietary sources — have a reduced risk of developing early-onset colorectal cancer. The study included 94,205 women (aged 25-42 years) who were followed between 1991 and 2015. Women who consumed the highest average total vitamin D (450 IU per day) demonstrated significantly reduced risk compared with those consuming < 300 IU per day. Associations between vitamin D levels and colorectal cancer have been documented over the years and are the subject of 10 recently completed or ongoing clinical trials. Few studies, however, have focused on early colorectal cancer and vitamin D intake.

Severe vitamin D deficiency has been linked to poor bone and muscle health, calcium absorption, immunity, and heart function, as well as colon, blood, and bowel cancers. This is in line with a recent prospective, population-based study of men which found that lower concentrations of vitamin D were associated with increased all-cause mortality. The research concluded that assessment of free 25-hydroxyvitamin D offers little added benefit to the current standard of total 25(OH)D, the major circulating form of vitamin D, because deficiencies in each are associated with a similar risk. The men were between 40 and 79 years of age and had a mean follow-up of 12.3 years. During that time, about a quarter (23.5%) of them died. After adjustment for key confounders, including body mass index, smoking, alcohol consumption, kidney function, number of comorbidities at baseline, and other factors, men with a total 25(OH)D level < 20 µg/L had a significantly increased risk for mortality compared with those who had normal levels of vitamin D, defined as > 30 µg/L (hazard ratio, 2.03; P < .001).

Given the potential benefits of vitamin D, questions have arisen as to whether patients with COVID-19 should be given supplementation. Findings from a randomized controlled trial earlier this year showed that high-dose vitamin D therapy had no significant effect on mortality or other key metrics in patients with moderate or severe COVID-19. For now, experts recommend incorporating regular supplementation for general health and well-being during the pandemic but have stopped short of suggesting the widespread use of vitamin D therapy in the acute setting of COVID-19.

Vitamin D supplementation may also be recommended for people of African Caribbean descent living at higher latitudes with lower sun exposure. A systematic review and meta-analysis included 19 articles published between 2005 and 2019 involving 5670 African Caribbean participants from six countries. The studies showed that average levels of 25(OH)D overall were 67.8 nmol/L, with levels > 50 nmol/L deemed sufficient. However, populations residing at high latitudes, such as the United States or United Kingdom, had insufficient mean concentrations of 40.9 nmol/L, suggesting a potential need for supplementation.

In regard to vitamin D obtained from sun exposure, a new study of more than 3000 men and women found that following sun-protective behaviors does not decrease bone mineral density (BMD) overall or increase osteoporotic fractures. The study goes a step further than previous research which found that sunscreen use does not compromise vitamin D synthesis and has little effect on circulating 25-hydroxyvitamin D levels. In the new study, researchers looked at three sun-protective behaviors: sunscreen use, staying in the shade, and wearing long sleeves. They found that the three behaviors were not associated with lower total or site-specific BMD z scores, nor were they linked with an increased risk for osteoporotic fractures.

From studies focused on associations with cancer and mortality to findings regarding supplementation and sun protection, an interest in new information on vitamin D resulted in this week's top trending clinical topic.

Read more clinical information on vitamin D deficiency.

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