The truth is, the body can produce vitamin D on its own. However, regular and adequate exposure to ultraviolet rays (like those found in certain UVB wavelengths of sunlight during certain times of the year at key latitudes and depending on your skin tone, how much you’re wearing, your sunscreen coverage—you get the point, vitamin D from sun isn’t as simple as it seems) is required to kick-start the process. But with key and essential roles in bone1, thyroid2, and immune3 health (to name just a few benefits), vitamin D seems to make the case for spending more time outdoors.* We consulted experts in nutrition science to see exactly how the sunshine-to-vitamin-D pipeline works, plus how much sun exposure is needed to support sufficient vitamin D status. But as we alluded to before, even direct sun exposure isn’t a foolproof way to produce vitamin D. As Holick explains, sunscreen and shade (which are important for protection against other skin health concerns) will get in the way, and location, altitude, season, skin tone, age, and time of day have to be considered as well. She notes also that an SPF of just 15 can slash vitamin D production by over 90%6. (And to be clear: We are fans of smart and intentional sun protection practices.) Season and location can limit vitamin D production even more severely. “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,” Holick explains. “Unless you’re going to be a lifeguard or a hunter-gatherer, you’re not going to make very much vitamin D.” (And even the lifeguard and forager aren’t making vitamin D from the sun in the northern latitudes for several months of the year). For people with darker skin tones, sunlight is an even less reliable source of vitamin D, as the presence of melanin naturally reduces vitamin D production in the skin. While 29% of U.S. adults7 are deficient in vitamin D, Black Americans are 15 to 20 times more likely8 to be extremely deficient [i.e., have serum 25-hydroxyvitamin D levels—that’s 25(OH)D for short—below 10 ng/ml]. For reference, 25(OH)D is your serum biomarker (i.e., from a blood test) of vitamin D status in your entire body. So, the answer is no—you can’t get vitamin D through a window. Ultimately, the question isn’t even that consequential, considering experts agree we shouldn’t be relying on sunlight as our sole source of vitamin D anyway. Unless, perhaps, you live close to the equator and spend most of your day in a bathing suit on the beach, you’ll have to turn to other high-quality, daily sources of D to reach sufficient vitamin D levels—and to reach truly optimal vitamin D status (i.e., at or above 50 ng/ml), smart supplementation is the way to go.* Even just to meet the baseline recommended dietary allowance (i.e., 600 IU for healthy adults, per the National Academies) to avoid bone health problems, one would have to drink more than six glasses of fortified milk9 a day, 12 whole eggs10, or a 3.5-ounce serving of sockeye salmon11, and experts agree—600 IU is not remotely enough of the fat-soluble nutrient to move the needle on vitamin D status in order to reach (and maintain!) healthy levels. As mentioned earlier, nationwide rates of frank vitamin D deficiency and insufficiency [i.e., 25(OH)D blood test results less than 20 ng/ml or 30 ng/ml] among adults is 29% and 41%7, respectively. But racial inequities clearly exist, with 82% of Black Americans12 and nearly 70% of Latino Americans12 experiencing D deficiency. If we just look at how much vitamin D we put in our mouths each day, nationally representative research demonstrates that between 9313% and 100% of the U.S. population fails to consume even a piddly 400 IU of vitamin D per day. With this in mind, Holick recommends all his clients take a vitamin D supplement daily, no matter the season. Drake agrees, stating the Linus Pauling Institute recommends generally healthy adults take 2,000 IU of supplemental vitamin D every day but noting that reaching ideal blood levels of vitamin D (i.e., above the 30 ng/ml “danger zone” for insufficiency and into that coveted 50 ng/ml range) may require an even higher dosage of supplementation. mbg’s vice president of scientific affairs Ashley Jordan Ferira, Ph.D., RDN, breaks down exactly how much vitamin D we need to achieve healthy serum levels: “Pharmacokinetic research14 shows that it takes 100 IU of vitamin D to increase a normal-weight adult’s serum D levels by about 10 ng/ml. So, that means that in order to achieve 50 ng/ml, you need 5,000 IU of vitamin D per day.” She elaborates, saying “Given that two-thirds of our nation is dealing with overweight or obesity, our daily vitamin D needs as a country are actually higher—but 5,000 IU is a great starting point.” If you’re trying to do some quick mental calculations to determine how many servings of milk, eggs, or fish you’d need to eat to consume 5,000 IU of vitamin D daily, we’ll save you the trouble—it’s a lot. Too much, one would be fair to argue. Simply put, daily vitamin D supplementation is the most effective way to reach sufficient vitamin D levels and maintain whole-body health.* (Looking for a truly effective D3 supplement that will help you achieve sufficient vitamin D status and keep it there? Check out our vitamin D supplement roundup.) As Ferira previously shared with mbg, this micronutrient is both a “vitamin and immunomodulator that wears many hats. Involved in innate and adaptive immune responses, the vitamin D receptor has been discovered in the majority of immune cells, and vitamin D demonstrates immunosuppressant, anti-inflammatory, antibacterial, and antiviral actions.”* More recently, a groundbreaking study conducted in Germany21 found vitamin D supplementation can literally add years to life and health span in older adults deficient in the essential vitamin.* In another study from the Journal of Internal Medicine, the potential mood-supporting effects of vitamin D supplements were tested against a placebo in over 300 Norwegian adults. After one year, those who received the vitamin D supplement showed significant improvements in their mood, while those in the control group (i.e., no vitamin D supplement) experienced no such benefits.* Experts recommend turning to high-quality vitamin D supplements to achieve and sustain sufficiency levels, and we’re partial to mindbodygreen’s own vitamin D3 potency+.* With 5,000 IU of vitamin D3 sourced from organic algal oil and thoughtfully paired with an organic trio of flax, avocado, and olive oils to support optimal absorption, our vitamin D is hard to beat.*
