Everything You Need to Know about Vitamin D in the Winter

Winter is upon us. And while the risk of vitamin D deficiency is always high in the winter (less sun equals less vitamin D), you could argue it’s even higher this winter—when COVID-19 has many of us spending the majority of our time indoors.

But COVID-19 also means that staying healthy and supporting our immune systems is more important than any winter in recent memory—and that means ensuring that we’re getting enough vitamin D.

So, the question is, with COVID-19 keeping so many of us indoors—while also making it more important to maintain adequate vitamin D levels now more than ever—how can we ensure we’re getting the vitamin D we need to stay healthy this winter?

What is Vitamin D—and why is it so important?

Before we jump into how to ensure we’re getting enough vitamin D this winter, let’s quickly cover what, exactly, vitamin D is, and why it’s such an important part of staying healthy.

“Vitamin D is often called the ‘sunshine’ vitamin,” says Nicole Avena, PhD, health and nutrition author, assistant professor of neuroscience at Mount Sinai School of Medicine, and visiting professor of health psychology at Princeton University. 

And for good reason! “Instead of being a vitamin obtained from diet and ingested, like most others, the human body actually synthesizes vitamin D in response to UV rays from the sun, specifically UVB,” says Avena. “The processes that our cells undergo to synthesize vitamin D are complex and require modifications to the vitamin’s molecular structure. These modifications occur in the liver and then in the kidneys.”

So, your body synthesizes vitamin D when you expose yourself to sunlight. And, from there, the vitamin goes on to support a variety of systems and functions within the body—all of which play a critical role in keeping you strong, fit, and healthy.

“Vitamin D actually aids in the precipitation and homeostasis of calcium and phosphorous in the bones which maintains bone density and keeps them strong,” says Avena. “Vitamin D is also involved in cell proliferation and differentiation by influencing gene expression…and supports the immune system by suppressing inflammatory immune cells.”

Vitamin D deficiency in the winter

Clearly, getting plenty of vitamin D is an important part of maintaining your health. But it can be challenging to get the healthy dose of sunshine you need to keep vitamin D levels high in the winter, when the days are cold and sunshine is in short order.

“Vitamin D is produced by the sun, and during the winter, days are cloudy and the sun sets early,” says Avena. “Cold weather also pushes people indoors and forces them to wear high-coverage clothing that does not expose their skin to the sun.”

That lack of sun exposure can lead to vitamin D deficiency—which is shockingly common and can carry some serious consequences. “Over one billion people on the planet are vitamin D deficient, qualifying it as an epidemic,” says Avena. “Prevalence of serious diseases like multiple sclerosis, rheumatoid arthritis, or diabetes can be associated with long-term and severe vitamin D deficiency, but more mild cases can still result in higher infection risk and a depressed mood.”

How to get the Vitamin D your body needs this winter

It’s a bit of a conundrum; getting enough vitamin D is a must in the winter—but getting enough vitamin D is more challenging in the winter because of the lack of sunshine. “If you are between the ages of 1-70, you should be getting about 15 mcg of vitamin D a day,” says Avena.

So, the question is, how can you make sure you’re getting the vitamin D your body needs this winter—even on the cloudiest, coldest, and most overcast day? Luckily, sunshine isn’t the only way to get vitamin D—you can also get your daily dose of vitamin D from your diet.

“Besides sunlight, vitamin D can also be found in some foods,” says Avena. “A great source of vitamin D is Chilean-farmed salmon, as in addition to having vitamin D, it contains omega-3 fatty acids, and doesn’t contain mercury. Other options include cod liver oil, trout, and some fortified milks and cereals.”

It can be challenging to get enough vitamin D from diet alone (particularly if you’re a vegetarian)—so if you’re having trouble hitting your 15mcg a day, you should also consider adding a vitamin D supplement to your regimen. (Vitamin D supplements come in a variety of forms and concentrations, so talk to your doctor to figure out the best supplement for you.)

And, if you can, get outside! While it won’t give you all the vitamin D you need to stay healthy until spring, it’s certainly not going to hurt. “Of course, it isn’t a bad idea to spend a little time outdoors getting some fresh air and sun exposure during winter months,” says Avena. “But you shouldn’t rely too heavily on getting vitamin D from the sun.”