Can sunlight make you skinny?

Winter is a bummer. Not only do you have to deal with bone-chilling temps, icy roads and rampant viral infections, but your jeans get extra tight thanks to winter weight gain.

It seems pretty obvious why so many of us pack on the pounds in the winter. We eat richer, high-calorie foods (especially during the holidays). And we snuggle up on the couch every night instead of venturing out in the cold for a walk or a run. It’s the perfect recipe for skyrocketing scales.

But what if there’s a hidden cause for your winter weight gain that you’ve never considered? A cause that could easily affect your weight in the winter but might even affect your weight other times of year depending on your lifestyle?

The cause I’m referring to is sun exposure.

It’s no secret that many of us get little to no sun in the winter months. This can take a toll on our vitamin D levels and contribute to seasonal affective disorder. But the latest research shows it may be contributing to winter weight gain too…

Peak D3

When you step out into the sunlight, your body begins the process of making vitamin D. But getting the ideal amount can be difficult because some of us can’t effectively absorb it. That’s just one of many reasons the vitamin D deficiency is an epidemic… MORE⟩⟩


Sunlight shrinks fat cells

Researchers from the University of Alberta recently found that the fat cells just beneath your skin shrink when they’re exposed to the sun.

According to researchers, this happens because sunlight contains blue light wavelengths. These blue light wavelengths seep into your skin and make their way to the fat cells just below the skin’s surface. When the sunlight reaches these fat cells, the lipid droplets inside of them begin to shrink and are released from the cell.

What does this mean? Well, it simply means that sunlight causes your cells to store less fat. That’s why researchers believe sunlight (or lack thereof) could play a role in winter weight gain.

“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 of the study, who is a professor of pharmacology and the director of University of Alberta’s Alberta Diabetes Institute.

This research was performed on cells in a lab. But Peter Light (whose name is a fun coincidence) and his fellow researchers believe it could have major consequences in several areas of human health. For one, Light thinks sunlight exposure in childhood could play a role in how many fat cells we develop during childhood — a number which likely persists into adulthood. He also thinks that maybe there’s a strong connection between sunlight, our circadian rhythm and our body fat.

“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,” said Light. “You gain weight in the winter, and then burn it off in the summer.”

Striking a sunlight balance

Not getting enough sunlight is bad for you. Besides its potential role in obesity, it also contributes to vitamin D deficiency, which heightens your risk for a bunch of chronic diseases. But getting too much is bad for you too because of the increased sun cancer risk. So when it comes to sunlight exposure, it’s all about striking the right balance.

The question is… how much sun is the perfect amount?

Well, that varies depending on your skin tone, the time of day, how much of your body is exposed and where you live. But for most people, sitting in the sun for 10-20 minutes per day without sunscreen in the spring and summer would do the trick.

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  1. Reduced sunlight may contribute to winter weight gain — MedicalXpress. Retrieved January 11, 2017.
  2. Ondrusova, et al. “Subcutaneous white adipocytes express a light sensitive signaling pathway mediated via a melanopsin/TRPC channel axis.” — Scientific Reports, 2017.
  3. How much sun is good for our health? — ScienceDaily. Retrieved January 11, 2017.
  4. Maria-Antonia Serrano, et al. “Solar ultraviolet doses and vitamin D in a northern mid-latitude.” — Science of The Total Environment, 2017; 574: 744.
Jenny Smiechowski

By Jenny Smiechowski

Jenny Smiechowski is a Chicago-based freelance writer who specializes in health, nutrition and the environment. Her work has appeared in online and print publications like Chicagoland Gardening magazine, Organic Lifestyle Magazine, BetterLife Magazine,, and