Can You Get Vitamin D Through A Window? Experts Reveal The Truth


When it comes to food, fortified milk and orange juice, as well as egg yolks and some kinds of (UV-irradiated) mushrooms contain small (as in, practically obsolete) amounts of vitamin D2 (the much less bioavailable and efficacious form of the micronutrient). Native food sources of vitamin D3 include some fatty fish—like salmon, for example.

Even just to meet the baseline recommended dietary allowance (ie, 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 milk a day, 12 whole eggs, or a 3.5-ounce serving of sockeye salmon, 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%, respectively. But racial inequities clearly exist, with 82% of Black Americans and nearly 70% of Latino Americans 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 93% and 100% of the US 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 (ie, 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 research 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.)


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