How To Achieve Healthy Vitamin D Levels Throughout The Winter

It's winter, which means for those of us living in cold parts of the country, days are short and access to sunshine is…unreliable, at best. This time of year, I get a lot of questions about vitamin D levels. 

Considering vitamin D deficiency and insufficiency impact a significant number of U.S. adults year-round (29% and 41%1, respectively), concerns over maintaining healthy vitamin D status are incredibly valid. 

While a large portion of our nation struggles with vitamin D sufficiency year-round, vitamin D status notoriously dips during the winter, especially for those in higher latitudes. 

In the 1980s, professor of medicine, physiology, and biophysics at Boston University medical center Michael Holick, M.D., Ph.D., authored foundational research on vitamin D synthesis2 that has continued to lead the evidence-based conversation on vitamin D throughout seasonal changes. 

In this research, Holick discovered the cutaneous vitamin D production (i.e., in the skin) of individuals living in Boston, Massachusetts during winter months was nonexistent. "If you are in Boston in the wintertime and you go outside for 15 minutes, you make zero vitamin D. In fact, you make no vitamin D from about November until the following March," he previously explained to mindbodygreen. 

And while this logic makes sense during the wintertime, sunshine isn't a sufficient source of vitamin D for most individuals any time of year (even during sunny summer months). Our exposure to sunshine and ability to convert it to vitamin D is impacted by numerous factors—including geographic location, season, climate, UV levels, pollution, clothing, sunscreen, age, and skin tone. 

Underscoring the importance of taking an (actually) effective dose of vitamin D in supplement form, in a 2021 study conducted in Korea, researchers found that a low-dose oral vitamin D supplement (i.e., 1,000 IU of D3 taken daily) helped modestly improve vitamin-D-deficient participants' serum 25(OH)D levels (i.e., the blood biomarker for vitamin D status) levels, only by an average 11 ng/ml after three months. (Comparatively, participants with vitamin D deficiency that chose sunlight exposure had no significant increase in average serum 25(OH)D levels.) 

That said, not all vitamin D supplements are created equal—many feature sub-efficacious doses, inadequate forms, and don't include fats to increase bioavailability. 

The sun isn't a sufficient source of vitamin D for most people, most of the year. Unless you happen to live close to the equator and spend plenty of time in the sun sans sunscreen (which we don't recommend, for the record), it's practically impossible to get adequate sunlight to maintain optimal vitamin D levels. (And if you live in a place with freezing temperatures and snow through the winter, forget about it!)