Vienna, Austria—Cold ambient temperatures increase vitamin A levels in humans and mice, according to a new study published inMolecular Metabolism. The vitamin A helps convert white adipose tissue into brown adipose tissue, which, a press release notes, stimulates fat burning and heat generation.

There are two types of fatty depots in humans and other mammals, the press release explains: white and brown adipose tissue. Excess calories are mainly stored in white fat, a process seen during obesity development. Brown fat, on the other hand, burns energy and generates heat. More than 90% of the body fat depots in humans are white; this fat is often found at the abdomen and upper thighs. Converting white fat to brown could be a therapeutic option to combat weight gain and obesity.

A research group led by Florian Kiefer, Division of Endocrinology and Metabolism, Department of Medicine III, MedUni Vienna, demonstrated that the moderate application of cold increases the levels of vitamin A in humans and mice, the press release says. Most vitamin A reserves are stored in the liver, and cold exposure appears to stimulate the redistribution of vitamin A towards the adipose tissue, leading to a higher rate of fat burning.
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When Kiefer and his team blocked the vitamin A transporter in mice via genetic manipulation, the cold-mediated rise in vitamin A and the conversion of white fat to brown were both blunted. The addition of vitamin A to human white fat cells, on the other hand, led to the expression of brown fat cell characteristics, with increased metabolic activity and energy consumption.

"Our results show that vitamin A plays an important role in the function of adipose tissue and affects global energy metabolism. However, this is not an argument for consuming large amounts of vitamin A supplements if not prescribed, because it is critical that vitamin A is transported to the right cells at the right time," explained Kiefer in the press release. "We have discovered a new mechanism by which vitamin A regulates lipid combustion and heat generation in cold conditions. This could help us to develop new therapeutic interventions that exploit this specific mechanism."