The Underrated Link Between Gut Health & Vitamin D

To fully support our gut health, it seems wise to address vitamin D status—after all, a staggering 29% and 41% of American adults2 are deficient or insufficient, respectively, in vitamin D.

"The vitamin D pathway is important in the regulation of immune responses and gut health. There are different genes regulated by the vitamin D receptor that can affect the integrity of the gut barrier and the immune defenses in the gut. With deficiency of vitamin D, one could hypothesize that changes in these aspects of the gut could lead to changes in the composition of the microbiota," says Adrian F. Gombart, Ph.D., a professor of biochemistry at Oregon State University's Linus Pauling Institute.

A healthy gut deserves the hype too. A diverse gut microbiome, which is a key indicator of a healthy gastrointestinal tract, protects against unwelcome invaders, helps to optimize the extraction of nutrients and energy, and contributes to healthy immune function3. Yes, it means better digestion but also better mood and cognition and much more.

And it's a two-way street. Not only does vitamin D influence the gut, but the gut also influences vitamin D—particularly, how well it's absorbed. Though it was previously thought to be a passive process, research suggests the absorption of vitamin D4 is affected by the upper digestive tract and proteins in the intestinal membrane. In other words, a healthier gut is able to absorb vitamin D more effectively. (That, and throwing some healthy fats in the mix.)

A vast number of American adults (93%, to be specific5) aren't consuming enough vitamin D daily. Because numerous factors affect the body's ability to synthesize vitamin D in the skin during exposure to sunlight, diet and high-quality supplementation are key to achieving optimal vitamin D status (and even diet isn't the most efficient way to get enough D—more on that later).*

These sun-confounding factors include time of day, time of year, location, skin tone, wearing SPF, air pollution, and even age. Combined with the reality of our lives—which are mostly spent indoors, these factors make getting enough D from the sun unrealistic. 

When it comes to dietary sources of vitamin D, it's not as simple as eating your vegetables. The only "veggie" (it's really a fungus) that contains the essential nutrient is irradiated mushrooms, which are exposed to UV light to get their vitamin D2 (a significantly less potent form of vitamin D).

Other modest sources of D include a list of animal products (like cod liver oil and eggs) and fortified foods like milk, O.J., and cereal. These are all fine, but the problem comes when you consider how much of those food items you actually need to consume for an optimal dose of 5,000 IU or more a day. According to mbg's vice president of scientific affairs, Ashley Jordan Ferira, Ph.D., RDN, that shakes out to 294 cubes of Cheddar cheese or 7 cups of irradiated mushrooms every single day. (Yikes!)