A Nutrition PhD Explains (& Debunks) A Common Vitamin D Myth

At team mbg, we can always count on our vice president of scientific affairs, Ashley Jordan Ferira, Ph.D., RDN, to weigh in on our burning food and nutrition queries. What's up with the new Dietary Guidelines for Americans? What's the deal with vitamin K2? What's the best form of zinc to take? And, on a much more juicy level: Are there any nutrition myths you see online that make you cringe? 

Vitamin D is one of the most well-documented players for immune support—an "old-school" nutrient, if you will.* However, it skyrocketed in popularity during the pandemic, after cross-sectional studies found vitamin D deficiency was higher in COVID patients than in the control groups1. As such, vitamin D finally got the recognition it deserved—although, says Ferira, it's important to truly digest what you're reading online. 

Most of us are deficient in vitamin D, says Ferira. And the research backs it up: 29% of U.S. adults are considered straight-up vitamin D deficient2, while 41% are vitamin D insufficient2. That's a huge nutrient gap—and yet, most health media outlets provide a single solution: Eat vitamin-D-rich foods. 

"That's a huge myth that I'd like to bust," Ferira notes. (She explains her reasoning further here, in case you're curious). "Telling someone to meet their vitamin D requirement through food is like giving you a quart of paint to go repaint your entire house."

To consistently achieve a 25(OH)D blood level greater than 30 ng/mL, research shows you need a minimum of 2,000 to 3,000 IU of vitamin D3 every day4. That's because 100 IU of vitamin D3 daily raises your 25(OH)D level by about 1 ng/mL. Ferira adds, "By the way, this rule of thumb applies to individuals with a healthy weight; those struggling with overweight or obesity will need two to three times more5 vitamin D3 daily." You can now see why it's pretty difficult to get through food alone.