The study in Nature Communications also revealed a new understanding of vitamin D and how it is commonly measured.
“We were surprised that the diversity of the microbiome – the diverse types of bacteria in a person’s gut – was closely related to the active vitamin D, but not the precursor form,” said senior researcher Deborah Cadeau, director of the Osteoporosis Clinic. At UC San Diego Health.
“Greater diversity in the gut microbiome is thought to be associated with better overall health,” Cadeau added.
Cadeau led the study for the Research Group to Study Osteoporosis in Men (MrOS), funded by the National Institute on Aging, a major multi-site effort that began in 2000.
Collaborated with Rob Knight, Ph.D., professor and director of the Microbiome Innovation Center at the University of California, San Diego, and co-authors Robert L Thomas, MD, Ph.D., Fellow in the Department of Endocrinology at UCSD, and Serene Linging Jiang, graduate student Graduated in biostatistics program at Herbert Wertheim School of Public Health and Human Longevity Sciences.
However, the largest randomized clinical trial to date, involving more than 25,000 adults, concluded that taking vitamin D supplements had no effect on health outcomes, including heart disease, cancer, or even bone health.
“Our study suggests the reason for this is that these studies measure only the elemental form of vitamin D, not the active hormone,” said Cadeau, who is also a professor at UC San Diego School of Medicine and Herbert Wertheim School of Public Health.
“Measures of vitamin D composition and breakdown may be better indicators of underlying health problems, and who is more responsive to vitamin D supplementation,” Cadeau added.
The team analyzed stool and blood samples contributed by 567 men enrolled in MROS. The participants lived in six cities in the United States, with an average age of 84 years and most of them reported being in good or excellent health.
The researchers used a technique called 16s rRNA sequencing to identify and measure the types of bacteria in each stool sample based on unique genetic identifiers. They used a method known as LC-MSMS to identify vitamin D metabolites (precursor, active hormone, and hydrolytic product) in each participant’s blood serum.
In addition to discovering a link between active vitamin D and the overall diversity of the microbiome, the researchers also noted that 12 specific types of bacteria were more common in the gut microbiomes of men who had too much active vitamin D. Beneficial fatty acids that help to maintain a healthy intestinal wall.
“The gut microbes are very complex and differ greatly from person to person. When we find associations, they are usually not as different as here,” Jiang said.
Because they live in different regions of the United States, the men in the study are exposed to different amounts of sunlight, a source of vitamin D. As expected, the men living in San Diego, California got the most sunlight and also had the most most vitamin D precursors.
But the team unexpectedly found no link between where the men lived and their levels of the active vitamin D hormone.
Cadeau added, “It’s important to what extent your body can metabolize that into active vitamin D, and perhaps this is what clinical trials should measure to get a more accurate picture of the vitamin’s role in health.”
Thomas added, “In medicine, we often find that more is not necessarily better. So in this case, it may not be about how much vitamin D you supplement, but how you encourage your body to use it.”
Cadeau pointed out that the study was based on a single, timely uptake of the microbes and vitamin D found in the participants’ blood and feces, and that these factors can fluctuate over time depending on the environment , the diet, the sleeping habits, medicines, etc.
More studies are needed to better understand the role bacteria play in vitamin D metabolism and to determine whether a microbiome-level intervention can be used to improve current treatments to improve bones and possibly other health outcomes, the team said.