In a study from January published in Nutrition Research, researchers established a connection between vitamin D and gut health as part of the MetA-Bone Trial, evaluating how a fiber supplement could affect the bone health of children ages nine to 14 from South Florida.

But before the 213 children and adolescents started taking the fiber supplement, researchers tested their vitamin D levels—and found that 68% of the children had suboptimal levels. 

“Because South Florida is an area with plenty of sunshine year-round, this was both startling and concerning,” wrote study co-author Jacqueline Hernandez and Cristina Palacios in a Washington Post article on the findings. That is especially alarming, as people primarily get their vitamin D from sunlight.

Roughly 15% of children and adolescents in the U.S. were vitamin D deficient in 2017, according to a study published in Pediatric Research in November 2024. While vitamin D deficiency has slightly decreased over time in the general U.S. population, it is especially high among non-Hispanic Black children.

How vitamin D impacts gut health

Research has shown that vitamin D helps receptors in your gut improve calcium absorption, and strengthens your intestinal barrier, which allows your gut to absorb nutrients while keeping out harmful bacteria.

Other research suggests that vitamin D deficiency can weaken the intestinal barrier, allowing substances from the intestine to enter the bloodstream, causing inflammation. That disruption of the intestinal barrier is linked to several diseases including liver disease, Type 1 diabetes, obesity, celiac disease, inflammatory bowel disease and colon cancer.

“We found that children with suboptimal vitamin D levels had a higher risk of damaging their intestinal barrier compared with children with optimal vitamin D levels,” the authors wrote in the Post. “This finding suggests that even in healthy children, suboptimal vitamin D levels may compromise the gut and increase the risk of developing chronic diseases at an early age.”

How much vitamin D do you need?

Vitamin D helps maintain and build bone mass, while helping support immune health, cognitive functioning, and mood regulation. The daily recommended dietary allowance for vitamin D is 600 IU for those aged one to 70, while older adults are recommended to take 800 IU per day. The American Academy of Pediatrics recommends 400 IU of vitamin D per day for infants. 

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But don’t overdo it, as too much vitamin D can be toxic. An 89-year-old U.K. man died in part from vitamin D toxicity in 2023, though he did have several underlying conditions.

The Office of Dietary Supplements also notes that vitamin D can interact poorly with certain medications, including statins and steroids, which is why consulting your doctor is important.

How to boost your vitamin D levels

Research suggests that five to 30 minutes of sun exposure between 10 a.m. and 4 p.m., either daily or at least twice a week to the face, arms, hands, and legs without sunscreen can help you meet your vitamin D needs.

You can also get vitamin D through food, including:

• Fish like salmon, trout, and tuna
• Orange juice or milk fortified with vitamin D
• Mushrooms
• Yogurt
• Egg yolks

Check with your doctor to see if you might benefit from a vitamin D supplement.

For more on nutrition and supplements:

• How vitamin D supplements may help improve energy levels
• Meet the hot new superfood—dark green algae powder that’s full of vitamins, minerals, protein, and omega-3s
• Top nutrition expert shares the No. 1 mistake he sees in American diets
• Nutritionists offer these 6 ways to get back to a healthy diet
• You might be overdoing it on protein and not getting enough of another vital nutrient
• The 7 Best Greens Powders of 2025: Tested and Reviewed 2025