According to a study published in the journal Frontiers in Physiology, extra vitamin D can restore good bacteria in the gut, giving hope in the fight against risk factors for diabetes and heart disease.

It is well known that a diet high in fat can trigger a metabolic syndrome, characterized as obesity, insulin resistance, and non-alcoholic fatty liver diseases.

An international team of researchers from the United States and China has now discovered that vitamin D deficiency is necessary for this syndrome to progress in mice, with underlying disturbances in gut bacteria.

If the findings can be validated in humans, sun bathing and vitamin D supplements may be feasible and affordable approaches to improve or even prevent metabolic syndrome.

“A sufficient dietary vitamin D supplement can partially but significantly antagonize metabolic syndrome caused by high fat diet in mice,” said study co-lead author Professor Stephen Pandol, from Cedars-Sinai Medical Center.

“These are amounts equivalent to the dietary recommendations for humans.”

More specifically, the researchers have shown that a high fat diet affects the balance between good and bad bacteria in the gut. This induces modest fatty liver and slightly raises blood sugar levels in mice.

Remarkably, an insufficient supply of vitamin D aggravates the imbalance in gut flora, contributing to full-scale fatty liver and metabolic syndrome.

Vitamin D deficiency decreases the production of defensins, which are anti-microbial molecules essential to maintain healthy gut flora. As expected, an oral supply of a synthetic defensin recovers gut bacteria balance, decreases blood sugar levels and improves fatty liver.

In summary, a high fat diet alone is not enough to cause metabolic syndrome but it is needed in combination with vitamin D deficiency.

Accordingly, vitamin D supplementation improves metabolic syndrome in mice. The next step would be to validate the results in humans.

“Few studies have indicated that vitamin D supplementation may not improve metabolic disorders in humans,” said study co-lead author Dr. Yuan-Ping Han, a researcher at Sichuan University in Chengdu, China.

“However, these studies are largely based on long-term surveys, which may be hampered by poor compliance and insufficient dosage.”

“We are planning a clinical study to confirm the link of vitamin D deficiency with gut bacteria disruption, and its association with metabolic syndrome.”

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Danmei Su et al. Vitamin D Signaling through Induction of Paneth Cell Defensins Maintains Gut Microbiota and Improves Metabolic Disorders and Hepatic Steatosis in Animal Models. Front. Physiol, published online November 15, 2016; doi: 10.3389/fphys.2016.00498