Vitamin A boosts fat burning in cold conditions, research finds
Cold ambient temperatures increase vitamin A levels in humans and mice, which his helps convert "bad" white adipose tissue into "good" brown adipose tissue, stimulating fat burning and heat generation, according to new research published in the journal Molecular Metabolism. This fat transformation is usually accompanied by enhanced energy consumption and is therefore considered a promising approach for the development of novel obesity therapeutics, the researchers said.
In humans and mammals, at least two types of fatty depots can be discerned, white and brown adipose tissue. During obesity development, excess calories are mainly stored in white fat. In contrast, brown fat burns energy and thereby generates heat. More than 90 percent of the body fat depots in humans are white which are typically located at the abdomen, bottom, and upper thighs. Converting white into brown fat could be a new therapeutic option to combat weight gain and obesity.
For the study, the researchers found moderate application of cold increases the levels of vitamin A and its blood transporter, retinol-binding protein, in humans and mice. Most of the vitamin A reserves are stored in the liver and cold exposure seems to stimulate the redistribution of vitamin A towards the adipose tissue. The cold-induced increase in vitamin A led to a conversion of white fat into brown fat or browning, with a higher rate of fat burning, according to the study.
When the researchers locked the vitamin A transporter retinol-binding protein in mice by genetic manipulation, both the cold-mediated rise in vitamin A and the browning of the white fat were blunted. Fat oxidation and heat production were perturbed so that the mice were no longer able to protect themselves against the cold. In contrast, the addition of vitamin A to human white fat cells led to the expression of brown fat cell characteristics, with increased metabolic activity and energy consumption, the researchers said.
"Our results show that vitamin A plays an important role in the function of adipose tissue and affects global energy metabolism,” said Florian Kiefer, lead author of the study from the Medical University of Vienna, in a statement. “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. 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."