A new animal study published in the journal Frontiers in Physiology suggests vitamin D may play a crucial role in the prevention of metabolic syndrome by modulating the gut microbiome.
Metabolic syndrome (MetS) refers to a prediabetic syndrome that includes obesity, hypertension, elevated plasma glucose and elevated lipids. MetS raises the risk of heart disease, diabetes and stroke. It may lead to non-alcoholic fatty liver disease (NAFLD). Studies show that up to 34% of the American population has MetS.
A diet high in saturated fat or carbohydrates may contribute to MetS. Other important risk factors include genetics, aging, sedentary behavior, low physical activity, disrupted sleep, mood disorders, psychotropic medication use and excessive alcohol use. An imbalance of gut flora is also thought to be involved in MetS.
Studies have shown a relationship between low vitamin D levels and obesity, insulin resistance and NAFLD. In addition, research has suggested that vitamin D may modulate the gut microbiome by reducing the levels of harmful bacteria. Due to these findings, researchers recently conducted a study to investigate the role vitamin D may play in the development of metabolic syndrome among mice.
The mice were divided to receive one of four diets for 18-20 weeks:
- Group 1: Vitamin D, low fat diet
- Group 2: Vitamin D depleted, low fat diet
- Group 3: High fat with vitamin D diet
- Group 4: High fat, vitamin D depleted diet
After 18 weeks of feeding, the mice in groups 2 and 3 developed moderate NAFLD; whereas, the mice in group 4 developed severe NAFLD.
The mice that were fed a high fat diet depleted of vitamin D developed a more severe case of glucose intolerance and insulin resistance. The vitamin D depleted, low fat diet did not significantly affect glucose intolerance and insulin resistance.
The study discovered that mice fed a vitamin D depleted and high fat diet had significantly elevated levels of inflammatory markers compared to moderate increases in the mice fed with a high fat diet or vitamin D depleted diet alone.
The researchers stated,
“These findings indicated that lacking dietary vitamin D might exacerbate the high fat diet-exerted systemic inflammation, which consequently could cause insulin resistance and non-alcoholic steatohepatitis (NASH).”
The researchers also found that intestinal integrity was moderately disrupted in groups 2 and 3, but severely disrupted group 4.
The study also evaluated the effects of a high fat diet and/or vitamin D deficiency on the production of defensins, the anti-microbial molecules needed to maintain healthy gut flora. The researchers found that the mice given a high fat diet had moderately decreased levels of defensins; whereas, the mice given either of the vitamin D depleted diets showed severe reductions in defensins. Supplying the mice with synthetic defensins restored the balance of gut flora, decreased blood sugar levels and improved NAFLD.
The researchers concluded,
“Taken together, our results demonstrate that high fat diet feeding initiates fatty liver and insulin resistance in mice, but additional vitamin D depleted diet worsens the impact and results overt MetS and even NASH…”
As always with animal studies, it’s important to remember that the results may not be replicable in humans. Thus, we must wait for further clinical studies in humans to confirm these findings.
A researcher from the study, Dr. Yuan-Ping Han at Sichuan University, China, announced that a clinical study in humans is already underway. “We are planning a clinical study to confirm the link of vitamin D deficiency with gut bacteria disruption, and its association with metabolic syndrome,” stated Han.
Tovey, A. & Cannell, JJ. New animal study suggests vitamin D may play crucial role in the prevention of metabolic syndrome. The Vitamin D Council Blog & Newsletter, 2017.
Su, D. et al. Vitamin D Signaling through Induction of Paneth Cell Defensins Maintains Gut Microbiota and Improves Metabolic Disorders and Hepatic Steatosis in Animal Models. Frontiers in Physiology, 2016.