Vitamin D helps regulate calcium and phosphate in the body to maintain our bones, teeth, and muscles. Nowadays, studies confirm the beneficial effects of Vitamin D on the bowel, heart, skin, cell overgrowth, and blood sugar.
Vitamin D and maintaining immune defenses are also correlated . Current research found that over 80% of 200 COVID-19 patients in Spain had Vitamin D deficiency . Further limited studies and meta-analyses have observed that Vitamin D seems to reduce symptoms of COVID-19 as compared to standard care . However, more substantial data is needed to support its impact in decreasing mortality rates of hospitalized patients.
We now know that there is evidence to back up the benefits of Vitamin D in the body. Still, the research community debates its ability to prevent diseases. In particular, one study concluded that Vitamin D supplementation did not improve the bone strength of old adults in the US . Another clinical trial concluded that Vitamin D supplementation did not prevent cancer and cardiovascular disease in aging adults .
These mixed findings on the benefits of Vitamin D have been a mystery to scientists, until now. Researchers at the University of California (UC) San Diego recently revealed a possible explanation for this discrepancy and a new understanding of Vitamin D bioavailability .
The Inactive Form of Vitamin D
Like any other substance, Vitamin D comes in several forms. Typically, researchers determine Vitamin D levels in the body by conducting standard blood tests, which only detect an inactive form of Vitamin D stored in the body called 25 hydroxyvitamin D or 25(OH)D.
The body benefits from Vitamin D only when the inactive precursor metabolizes into its active form - 1,25 dihydroxyvitamin D or 1,25(OH)D. So no matter the amount of sun exposure or supplementation you take in, you only gain the benefits once activation of Vitamin D occurs in the body.
UC San Diego researchers have suggested that the Vitamin D paradox, where studies failed to establish a correlation in Vitamin D supplementation, blood inactive Vitamin D status, and positive health outcomes, might be due to scientists measuring in the blood 25(OH)D, the inactive form of Vitamin D, rather than its active form 1-25(OH)D.
Gut Microbiome and Vitamin D Link
In addition, UC San Diego researchers found a consistent association between 1-25(OH)D levels, the active form of Vitamin D, and the diversity and number of bacteria in the gut microbiome. In contrast, 25(OH)D, the precursor form of the vitamin, had a weak correlation with the “friendly” gut bacteria. The link between active Vitamin D levels and gut microbiome trumps other factors investigated in the study, such as antibiotic use, ethnic background, and even location.
Butyrate and Vitamin D Metabolism
The study also pointed out that participants with the highest levels of active Vitamin D have the most gut bacteria that produce butyrate. This short-chain fatty acid results from bacteria feeding on fibre and has been known to have potential benefits to support the gut lining, maintain the gut microbiome, and further support a competent immune system .
Researchers believe that butyrate-producing gut bacteria, rather than high quantities of inactive Vitamin D, control Vitamin D activation, which could explain these seemingly contradicting findings
Contrary to prior logic, participants living in sunnier places did not have significantly higher levels of active Vitamin D as other participants, despite synthesizing high amounts of inactive Vitamin D through the skin. Researchers believe that butyrate-producing gut bacteria, rather than high quantities of inactive Vitamin D, control Vitamin D activation, which could explain these seemingly contradicting findings.
Moreover, there is increasing evidence that the microbiome and immune system are interconnected and that active Vitamin D and butyrate may play extensive roles in this dynamic .
All of this points to butyrate helping our body transform the inactive precursor to the active form of Vitamin D, allowing us to reap all the benefits for optimal well-being.
Vitamin D supplementation and sunlight appear to be insufficient for optimal Vitamin D bioavailability and turnover. We need to encourage our bodies through gut microbial diversity, including butyrate-producing bacteria, to directly influence Vitamin D metabolism to its active form. Consequently, supplementing Vitamin D with butyrate ensures that we get all the benefits of Vitamin D to promote a sound mind and body while maintaining a favourable gut microbiome to support our immunity and overall well-being.