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The pounds mount for most people during the winter – the slacks or skirts getting just a bit snug around the middle as the cold months draw on. Traditional wisdom holds that it’s due to less activity, and more so-called “comfort foods.”

But one underlying cause may be a loss of a specific part of the spectrum of sunshine that shrinks fat cells just beneath the surface of our skin, according to a new study in the journal Scientific Reports.

Between one and five percent of blue light wavelengths invisible to the human eye penetrate skin and reduce the size of lipid droplets, thereby reducing the amount of fat they can hold, according to the scientists at the University of Alberta, in Edmonton.

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

The white adipose tissue was tested from human and rodent sources, with the human samples coming from patients undergoing abdominoplasties (“tummy tucks”).

All the samples were exposed to hours of chronic blue light exposure – showing the effects of the shrinkage, they report. The current in the tissue is mediated by melanopsin, which is coupled to transient receptor potential canonical cation channels, according to the paper.

“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,” said Peter Light, senior author, a pharmacologist who heads the Alberta Diabetes Institute.

The scientists did not set out to find a potential weight-loss mechanism in the biochemistry of the lipids. Instead, they had set out to bioengineer fat cells to produce insulin for diabetes patients based on light responses.

“It was serendipitous,” said Light. “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.”

The blue-spectrum light may be tied to circadian rhythms – meaning the body naturally stores more fat to contend with colder climes, Light added, in a school statement on the work.

The connection is only preliminary, Light and his colleagues caution – adding that pursing sunshine exposure merely for weight gain is not yet safe or recommended until more research better delineates the blue-light effects. 

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