The Surprising Health Benefit of Vitamin D

Vitamin D is known as the “sunshine vitamin” that’s celebrated for its role in strong bones and a healthy immune system. But beyond keeping your skeleton sturdy and fending off viruses, it has a surprising benefit that goes much deeper—your gut health. 

A healthy gut does more than digestion. It also supports a healthy immune system, produces hormones, influences metabolism and keeps inflammation in check. And vitamin D is a key nutrient for a well-functioning gut. To help you learn more, we spoke with registered dietitians to unpack this often-overlooked benefit.

What to Know About The Hidden Gut Health Benefits of Vitamin D

Vitamin D isn’t just a vitamin—it’s also a hormone, and it plays a powerful role in gut health. Here’s how.

Protects Against Harmful Pathogens in the Gut

Vitamin D plays a behind-the-scenes role in protecting your digestive tract. Erin Kenney, M.S., RD, a registered dietitian, explains that it activates the production of antimicrobial peptides like defensins and cathelicidin—natural compounds that keep harmful bacteria, viruses and other pathogens in check. She adds that vitamin D also helps your immune system distinguish between invaders and your body’s own healthy cells. In doing so, vitamin D assists in reducing the risk of excessive inflammation and autoimmune disorders.

Increases Beneficial Bacteria in the Gut

Not only does vitamin D help prevent the overgrowth of harmful bacteria, but it may also encourage the growth of beneficial microbes in your gut. Hannah Van Ark, M.S., RD, a registered dietitian, explains that vitamin D is specifically linked to greater populations of friendly bacteria like Lactobacillus and Bifidobaterium. She points to a study in women with vitamin D deficiency where supplementation significantly increased gut microbial diversity. “A diverse microbiome is generally more resilient and better able to support digestion, immune balance and overall well-being. This highlights the importance of adequate vitamin D levels for many areas of health.”

Strengthens the Gut Lining

Vitamin D also helps to maintain a healthy gut lining, which is your digestive system’s protective barrier. “Our intestines are semi-permeable, allowing certain helpful things to absorb into our bloodstream (e.g., nutrients), and prevents other harmful things from entering (e.g., pathogenic bacteria). Therefore, it’s important to maintain a healthy intestinal barrier to protect ourselves,” says Meghan Pendleton, M.S., RD, a registered dietitian. Kenney further explains that vitamin D provides this protection by supporting the production of tight junction proteins in intestinal cells. These tight junction proteins help maintain the integrity of the gut lining and reduce intestinal permeability, or “leaky gut”, a condition often linked to autoimmune disease, food sensitivities and skin issues.,

Influences Gut-Brain Communication

“Vitamin D receptors are found throughout the gut and play a role in signaling along the gut–brain axis—the two-way communication system between the digestive tract and the central nervous system,” says Van Ark. 

She explains that vitamin D helps regulate gut inflammation and the production of neurotransmitters like serotonin—around 95% of which is produced in the small intestine. When the gut is stable and well-nourished, it can send steadier, more accurate messages to the brain through the gut-brain axis. “Because this connection affects digestion, mood and even stress responses, vitamin D sufficiency could help support both mental and gastrointestinal well-being.”

How to Get More Vitamin D

Vitamin D comes in a highly bioavailable form called D3 (cholecalciferol), derived from animals or algae, and a less bioavailable form, D2 (ergocalciferol), found in plants. Understanding the difference can help you make informed choices about boosting your vitamin D intake, whether through food, supplements or sunlight. Here’s a closer look at each.

From Food

Unlike other nutrients, vitamin D can be tricky to obtain from food alone. Van Ark points out that only a handful of foods contain vitamin D, including:

• Fatty fish: Salmon, mackerel, sardines and trout are among the richest natural sources of vitamin D3.
• Mushrooms: Mushrooms that have been exposed to sunlight or UV rays produce vitamin D2. While less potent than vitamin D3, it can still support overall levels.
• Fortified foods: Many dairy products, plant-based milks, orange juice and some cereals are fortified with vitamin D. Fortified dairy products typically contain vitamin D3 while plant-based milks may be fortified with either vitamin D2 or vitamin D3.
• Eggs: Eggs contain a very small amount of vitamin D, mostly concentrated in the yolk.
• Meat and Dairy: Some animal products, like beef and cheese, contain minor amounts of vitamin D.

From Supplements

If you find it difficult to get enough vitamin D from food, supplements can help fill the gap. “The most effective form of vitamin D for supplementation is vitamin D3 (cholecalciferol), as it raises and maintains serum vitamin D levels more efficiently than vitamin D2,” says Kenney. “For the best absorption, consider choosing a liposomal or soft gel form suspended in oil or an emulsified drop, especially if you have fat malabsorption or digestive issues.”  While most over-the-counter supplements provide 600–2,000 IU of vitamin D, it’s important to work with your healthcare provider to determine the right dose for you. 

To further enhance absorption, Kenney suggests taking your supplement with a meal that contains fat, since vitamin D is fat-soluble. She also recommends pairing it with vitamin K2, which may help to help direct calcium into your bones.  Ensuring adequate magnesium intake is important as well, since magnesium is required for vitamin D metabolism. Aim to get most of your magnesium through food, and consider a supplement if necessary. 

From Sunlight

“The most efficient way to get vitamin D is from the sun,” says Kenney. Sunlight contains UVB rays that can penetrate your skin and kickstart the production of vitamin D—no cooking or pill bottles required. However, the season, time of day, weather and amount of melanin in your skin can affect UVB exposure and vitamin D synthesis. Most experts agree that 5 to 30 minutes of sun exposure on the face, arms, hands and legs between 10 a.m. and 4 p.m. is enough for vitamin D production. While midday sun is best, it also poses the highest risk of sunburn and skin damage, so it’s important to limit time in the sun during peak hours and always apply sunscreen.

Our Expert Take

Vitamin D is a superhero for your health. It not only supports strong bones and your immune system, but it plays a crucial role in gut health. From supporting a balanced gut microbiome and a strong gut lining to bolstering your immune system and influencing gut-brain communication, vitamin D plays a vital role in digestive and overall health. To boost vitamin D levels, eat vitamin-D rich foods, get some safe sun exposure and consider a supplement if recommended by your healthcare provider.