Your Vitamin D Levels Can Dip In The Winter — Here's What To Do

Just in case you somehow didn't know (really, though, where have you been?), vitamin D plays a major role in all sorts of essential body processes. The nutrient helps regulate the function of genes associated with the immune system, supports a healthy thyroid, contributes to strong bones, and more.* It's no wonder it's been in the news so much the past year and some change!

As mbg's director of scientific affairs Ashley Jordan Ferira, Ph.D., RDN, points out, "Whether for your bone health or immune system, adequate vitamin D is attainable—and a no-brainer investment in your wellness."*

And while getting enough vitamin D—at least 3,000 IU a day (i.e., a starting point) for healthy adults—is absolutely doable (especially with a high-quality, high-potency supplement), that certainly doesn't mean that everyone's doing it.*

That leaves us, then, with the sun. "[Vitamin D] is the 'sun vitamin', meaning that its production starts with the influence of full-spectrum sunlight," says Jeffrey Bland, Ph.D., functional medicine expert, mbg Collective member, and founder of Big Bold Health.

Though spending 30 minutes in the sun daily may be enough for many people in the warmer months, that's not necessarily the case in the wintertime. "The long nights and short days of winter, particularly in northern latitudes, result in lower vitamin D levels in the body," he says. (And those aren't the only factors that limit your ability to get vitamin D from the sun, either.)

Unfortunately, it's not necessarily obvious when your body needs more vitamin D, which makes spotting an insufficiency at home next to impossible. According to Bland, the signs are "very subtle" and could include fatigue, suboptimal immune function, changes in mood, and muscle discomfort.

And these indications become more concerning when paired with this stat: Over 40 percent of U.S. adults2 have suboptimal vitamin D levels that meet the definition clinical insufficiency.

Now that you know why vitamin D levels can dip in the winter, you're probably wondering what you can do about it. Of course, there's no reason not to get outside more this season—especially since getting some sun can also boost your mood and feel especially restorative during pandemic times. "On a clear winter day, get outside," Bland says. "Get your face and arms exposed to sunlight for at least 30 minutes."

Of course, though, if you live in a colder climate that makes baring those arms a no-go—or is far north enough that you won't be able to produce vitamin D from sun exposure—you won't be able to depend on time outside to keep that vitamin D level stable.

And Ferira explains, "when we say 'north,' that's actually still in the South, like North Carolina or higher. In other words, if you live above 35 degrees north latitude, the angle of the UVB rays from the sun aren't going to effectively photosynthesize vitamin D3 in your skin, even if you did have a bathing suit on."

She goes on to say that for those below the 35th parallel north, "you still have clothing, skin tone (melanin content), age, pollution, sunscreen, and other factors that limit the sun from being your daily, much less lifetime, go-to vitamin D source."

So what is a lifetime, go-to vitamin D source? Ferira concludes: "A robust vitamin D3 supplement taken daily is that reliable and safe source."*