- The recommended daily dose of vitamin D for adults is 600 International Units (IU).
- Without the proper amount of vitamin D, individuals may experience fatigue, muscle weakness, and bone pain.
- Experts recommend looking for vitamin D supplements with a third-party testing stamp, like NSF, USP, BSGC, and Informed-Sport.
How can you ensure your vitamin D supplement is being its most effective?
Vitamin D, the “sunshine vitamin,” serves numerous purposes in the body, from supporting healthy bones to boosting immunity. But the age-old question remains—is it possible to have too much of a good thing?
Recent debate has focused on the effects of large doses of vitamin D administered weekly, rather than the traditional smaller daily dose. Which option provides a better opportunity for absorption? Which is healthier? Researchers continue to discuss the best way to supplement this critical vitamin.
By and large, however, most experts continue to recommend smaller daily doses (outside of a few specific health circumstances). Here’s what to look for in a vitamin D supplement and why, for most people, a slow and steady dosage is often best.
What Experts Say About Vitamin D Dosage
According to the National Institutes of Health Office of Dietary Supplements, the recommended amount of daily vitamin D for adults aged 19–70 is 15 micrograms or 600 International Units (IU). The tolerable upper limit for adults—the highest amount considered safe—is 4,000 IU.
You’ll find a wide variety of vitamin D dosages in pills, gummies, and other supplements. While many contain IU in the hundreds, some contain 5,000 IU or more.
One reason for the variation in OTC amounts of vitamin D: various studies have shown that a higher vitamin D dose administered weekly could result in some positive health outcomes for certain groups.
A 2023 meta-analysis, for example, found that very high weekly dosages (up to 21,000 IU) reduced intensive care unit hospitalization and death in people with COVID-19. In another study from 2018, pregnant women deficient in vitamin D3 received either 1,000 IU daily or 50,000 IU weekly. The group who received the high weekly dose had no adverse side effects and had higher levels of vitamin D in their blood after 10 weeks.
While there may be special circumstances where a higher weekly dosage is warranted, most in the medical community remain cautious about recommending this route for the general population.
“Most patients who require vitamin D supplements should take a small daily dose,” Nate Wood, MD, Instructor of General Medicine at Yale Medicine, told Health. “For patients who are severely deficient in vitamin D, a larger weekly dose may be prescribed for the short-term.”
Vitamin expert Arielle Levitan, MD, co-founder of Vous Vitamin, agreed: “Absorption is better and more constant, and taking a daily dose gives you more flexibility with regard to actual dosing.”
Dr. Levitan also explained the variety of factors that goes into finding proper vitamin D dosage. “The exact amount each person should take varies depending on numerous factors. Things that can influence needs include where you live, ethnicity, other medical conditions such as GI illnesses, and specific symptoms,” she said.
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Vitamin D Deficiencies in the US
Vitamin D comes in endless supply from the sun, and several foods contain high amounts as well. Salmon, tuna, egg yolks, fortified cereals, and certain mushrooms are high in the “sunshine vitamin.”
Still, a surprisingly high percentage of Americans aren’t getting enough. Data from 2022 revealed that approximately 41% of the U.S. population had vitamin D insufficiency, with a higher prevalence of deficiencies in women, non-Hispanic Black Americans, and people aged 20–29.
According to Harvard’s T.H. Chan School of Public Health, the median intake of vitamin D from food and supplements in women 51 to 71 years old is 308 IU daily, with only 140 IU coming from food. That’s a far cry from the 600 IU beneficial for good health.
Vitamin D deficiency can show up with symptoms like fatigue, muscle weakness, and bone pain. But even if you’re deficient, you might not know it. The only way to determine whether your vitamin D levels are low is a blood test.
If your levels are sufficient (50 nmol/L or above), your doctor may not recommend supplementation. For lower levels, however, a regimen of daily D is likely a good idea.
“For patients who don’t spend much time in the sun, take a daily multivitamin, or regularly eat foods fortified with vitamin D, 600 to 800 IU of vitamin D per day may be recommended,” noted Dr. Wood. “Older adults and pregnant women may need more.”
How to Ensure Vitamin D Absorption
Vitamin D is one of only four vitamins that require a source of fat for absorption. For this reason, Dr. Levitan recommends taking it with a meal that contains some fat. This doesn’t have to include heavy foods like burgers or butter—any source of fat will do.
Some people prefer to take a vitamin D supplement at a specific time of day, such as first thing in the morning or right before bed, but the science isn’t clear on whether this increases effectiveness. The best time of day to take your supplement is probably whatever time works best for you and helps you stick to a routine.
Finding the Right Vitamin D Supplement
If you’ve decided to boost your vitamin D levels, you’ll have a vast array of supplements to choose from. This micronutrient is available in pills, chewables, liquids, and more. Some people even opt for vitamin D-enhancing sunlamps!
To choose a high-quality supplement, look for a label that indicates third-party testing. This means a supplement brand has allowed its product’s contents to be verified by an outside organization. Third-party testing companies include NSF, USP, BSGC, and Informed-Sport—so seek out vitamins with their seal of approval.
As for whether to choose vitamin D2 or D3, either will increase your blood levels, but most research shows that D3 increases levels to a greater extent and maintains them longer than D2. You also may want to purchase a supplement that includes magnesium, since this mineral helps activate vitamin D.
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