A potential explanation for winter weight gain – Fat cells are sensitive to sunlight: study

11 Jan 2018 --- A breakthrough study by University of Alberta researchers has shown that the fat cells that lie just beneath our skin shrink when exposed to the blue light emitted by the sun. According to the researchers, the insufficient sunlight exposure people living in a northern climate get eight months of the year may be promoting fat storage and contribute to the typical weight gain some of us have over the winter.

“When the sun's blue light wavelengths – the light we can see with our eye – penetrate our skin and reach the fat cells just beneath, lipid droplets reduce in size and are released out of the cell. In other words, our cells don't store as much fat,” says Peter Light, senior author of the study, who is a professor of pharmacology and the director of UAlberta's Alberta Diabetes Institute.

Light cautions the finding is only an initial observation and that pursuing exposure to sunlight is not a safe or recommended way to lose weight. “For example, we don't yet know the intensity and duration of light necessary for this pathway to be activated.”

However, he adds the novel discovery opens up new avenues of future scientific exploration which could someday lead to pharmacological or light-based treatments for obesity and other related health issues such as diabetes.

“Maybe this mechanism contributes to setting the number of fat cells we produce in childhood – thought to stay with us into adulthood,” he speculates.

“Obviously, there is a lot of literature out there suggesting our current generation will be more overweight than their parents and maybe this feeds into the debate about what is healthy sunshine exposure.”

The researchers made the discovery while investigating how to bioengineer fat cells to produce insulin in response to light to help Type 1 diabetes patients.

“We noticed the reaction in human tissue cells in our negative control experiments, and since there was nothing in the literature, we knew it was important to investigate further,” explains Light. Based on the finding, the fat cells we store near our skin may be a peripheral biological clock.

“It's early days, but it's not a giant leap to suppose that the light that regulates our circadian rhythm, received through our eyes, may also have the same impact through the fat cells near our skin."

He explains that the molecular pathway they discovered was first identified as being activated by the eye when exposed to the blue wavelengths in sunlight.

“Perhaps that pathway – exposure to sunlight that directs our sleep-wake patterns – may also act in a sensory manner, setting the amount of fat humans burn depending on the season. You gain weight in the winter, and then burn it off in the summer,” Light says, adding that this could be evolutionary process, supported by the fact that unlike many other mammals, our fat is spread out all over our bodies just underneath our skin.