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

Woman Smiling in Dappled Light On a Spring Day
Image by Sophia Hsin / Stocksy
November 27, 2020

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."*

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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.*

In fact, most people in the U.S. (we're talking 93 to 100% of adults1) do not consume modest, much less adequate, amounts of vitamin D through diet alone—and the lack of sunshine many people face during the winter certainly doesn't help with meeting those needs.

Why vitamin D insufficiencies can flare in the winter.

The two main natural sources of vitamin D are food and sunshine—but getting all of your daily vitamin D from diet alone is a challenge, since it isn't present in many major food groups. (Plus, even the better food sources of vitamin D out there, including the fortified ones, don't offer all that much.)

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. adults have suboptimal vitamin D levels that meet the definition clinical insufficiency.

"So if a person experiences any of these [signs], it would be smart to check their blood levels for vitamin D." If you're heading to the doctor this winter, ask for a serum 25-hydroxyvitamin D blood test—25(OH)D for short. Anything above 30 ng/ml is technically considered sufficient, though evidence suggests that 50 ng/ml is a more ideal level to aim for if you want to support optimal health throughout life.*

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How to get back on track.

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."*

As the challenges of sun reliance are evident, taking a high-quality, high-potency vitamin D supplement is a smart move.* To attain that ideal level of at least 50 ng/ml, many people will need at least 5,000 IU of vitamin D3 per day, and other individuals will simply need more.* With this simple routine tweak, you'll help your body help you all winter long and beyond.

If you are pregnant, breastfeeding, or taking medications, consult with your doctor before starting a supplement routine. It is always optimal to consult with a health care provider when considering what supplements are right for you.
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Emma Loewe
Emma Loewe
mbg Sustainability + Health Director

Emma Loewe is the Sustainability and Health Director at mindbodygreen and the author of Return to Nature: The New Science of How Natural Landscapes Restore Us. She is also the co-author of The Spirit Almanac: A Modern Guide To Ancient Self Care, which she wrote alongside Lindsay Kellner.

Emma received her B.A. in Environmental Science & Policy with a specialty in environmental communications from Duke University. In addition to penning over 1,000 mbg articles on topics from the water crisis in California to the rise of urban beekeeping, her work has appeared on Grist, Bloomberg News, Bustle, and Forbes. She's spoken about the intersection of self-care and sustainability on podcasts and live events alongside environmental thought leaders like Marci Zaroff, Gay Browne, and Summer Rayne Oakes.