Plenty of us are familiar with the holiday weight phenomenon. But while it is true that during the holidays we're more exposed to delicious food than the rest of the year, some studies have shown that in winter, we continue to pack on the pounds despite conscious efforts to lose them. Why?
A new study — by researchers at the University of Alberta in Edmonton, Canada — reveals an unexpected culprit for winter weight gain: the absence of sunlight.
The researchers, who were led by the auspiciously named Peter Light — from the Alberta Diabetes Institute — examined the effect of sunlight on subcutaneous fat cells, or white fat cells that can be found right beneath our skin.
The results of their investigation make this a breakthrough study, and it was recently published in the journal Scientific Reports.
How sunlight 'burns' fat
Light and team examined the so-called subcutaneous white adipose tissue (scWAT), which, as the authors explain, is the "major fat depot in humans and a central player in regulating whole body metabolism."
Accidentally, they discovered that scWAT cells tend to shrink under the effect of the sun's so-called blue light — that is, the visible type of light that boosts attention and mood during the day.
To further test their discovery, the scientists took samples of scWAT from patients undergoing weight loss surgery and examined the effect of the sun's blue light on the fat cells.
This is what they found:
"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."
Winter weight gain explained
"If you flip our findings around," Light says, "the insufficient sunlight exposure we get 8 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."
"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 adds.
The findings may pave the way for new weight loss strategies or light-based therapies in the treatment of obesity and diabetes.
However, Light cautions against taking these findings too literally and pursuing sunlight exposure in order to lose weight, as there are still many variables that remain unknown.
"For example," he explains, "we don't yet know the intensity and duration of light necessary for this pathway to be activated."
Additionally, he notes, "[T]here 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."
Either way, this exciting discovery "certainly holds many fascinating clues for our team and others around the world to explore," Light concludes.