Reduced sunlight may contribute to winter weight gain

Reduced sunlight may contribute to winter weight gain

We may have a new reason, in addition to vitamin D generation, to bask in a little sunshine.

A breakthrough study by researchers has shown the fat cells that lie just beneath our skin shrink when exposed to the blue light emitted by the sun.

"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," said  senior author of the study.

"If you flip our findings around, the insufficient sunlight exposure we get eight months of the year living in a northern climate may be promoting fat storage and contribute to the typical weight gain some of us have over winter," senior author added.

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."

"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.

Based on the finding, the fat cells we store near our skin may be a peripheral biological clock, said the senior author.

"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."

The senior author explained that the molecular pathway they discovered was first identified as being activated by the eye when exposed to the blue wavelengths in sunlight.

Authors discovered a novel blue light-sensitive current in human scWAT that is mediated by melanopsin coupled to transient receptor potential canonical cation channels. This pathway is activated at physiological intensities of light that penetrate the skin on a sunny day.

Daily exposure of differentiated adipocytes to blue light resulted in decreased lipid droplet size, increased basal lipolytic rate and alterations in adiponectin and leptin secretion. 

"That's why you are not supposed to look at digital devices before bed because they emit the same blue light the sun does, that signals us to wake up," senior author explained.

"Well, 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."

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, senior author added.
"Our initial first observation certainly holds many fascinating clues for our team and others around the world to explore."