Vitamin D and Gut Microbiome
Several studies have suggested that a person’s vitamin D levels have an important impact on overall, long-term health. A study from the University of California San Diego explored the connection between the gut microbiome and a person’s levels of active vitamin D. The research team learned that there is an important link between the two, and without a healthy gut, vitamin D may not work. (1, 2)
This study also contributed new understandings about vitamin D and how it’s measured. Although vitamin D can appear in different ways in the body, we usually only measure one of its forms because it’s the only one that appears on standard blood tests. This form is an inactive precursor, which the body has the ability to store. But in order to use it, the body has to metabolize the precursor form of vitamin D into an active form. (1, 2)
Measuring Vitamin D
Deborah Kado, MD, is a senior author on the study and director of the Osteoporosis Clinic at UC San Diego Health. “We were surprised to find that microbiome diversity — the variety of bacteria types in a person’s gut — was closely associated with active vitamin D, but not the precursor form,” Kado told UC San Diego News. “Greater gut microbiome diversity is thought to be associated with better health in general.” (1)
Kado believes that only measuring the precursor form of vitamin D is the reason for disparities in studies on vitamin D and health. Many studies have demonstrated that low vitamin D levels are connected to an increased risk of heart disease, cancer, and other diseases. But a large randomized clinical trial, with 25,000 subjects, found that vitamin D supplements don’t have any effect on these or other health outcomes. (1)
“Our study suggests that might be because these studies measured only the precursor form of vitamin D, rather than active hormone,” Kado said to UC San Diego News. “Measures of vitamin D formation and breakdown may be better indicators of underlying health issues, and who might best respond to vitamin D supplementation.” (1)
Active Vitamin D and Microbiome Diversity
The UC San Diego study involved 567 male participants whose average age was 84 years. The participants lived in six cities in the United States and were described as very physically active. The majority of the men reported taking vitamin D supplements. (1, 2)
By analyzing the participants’ blood and stool samples, the research team found that there is a connection between active vitamin D and microbiome diversity. They also noticed that the men with the highest levels of vitamin D more often had 12 specific types of bacteria in their gut microbiomes. (1, 2)
The men living in the sunniest city involved in the study, San Diego, CA, had the most precursor form of vitamin D. However, there was no connection between the amount of sun exposure in the cities where the participants lived and their levels of active vitamin D. (1, 2)
“It seems like it doesn’t matter how much vitamin D you get through sunlight or supplementation, nor how much your body can store,” Kado stated. “It matters how well your body is able to metabolize that into active vitamin D, and maybe that’s what clinical trials need to measure in order to get a more accurate picture of the vitamin’s role in health.” (1)
More studies are necessary to gain a greater understanding of the connection between the microbiome and vitamin D. But this study raises exciting possibilities in learning how our bodies can better use vitamin D to lower disease risk and improve overall health.
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