Ulcerative colitis is one of the two main types of inflammatory bowel diseases (IBD), which are chronic inflammatory conditions of the gastrointestinal (GI) tract.

They are characterized by diarrhea, fatigue, abdominal pain, bloody stools, malnutrition, and unintentional weight loss, among other symptoms.

Vitamin D is a fat-soluble vitamin primarily known for its beneficial effects on bone health. However, evidence suggests that the vitamin also plays a vital role in immune function and offers potent anti-inflammatory effects.

Thus, it may benefit people living with inflammatory diseases like ulcerative colitis.

In fact, multiple studies show that low vitamin D levels may increase your risk of developing IBD.

People with ulcerative colitis tend to have low vitamin D levels due to malabsorption, inadequate dietary intake because of their IBD symptoms, low sunlight exposure, trouble converting the vitamin to its usable form, or increased excretion.

Therefore, some researchers believe that giving vitamin D supplements to people with ulcerative colitis may be an effective, low cost treatment.

This article reviews the research to tell you whether vitamin D may support the management of ulcerative colitis symptoms.

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Scientific evidence has linked vitamin D deficiency to an increased risk of ulcerative colitis, disease severity, hospitalization rates, need for surgery, and even colorectal cancer risk.

For this reason, researchers have focused on studying the beneficial effects of vitamin D supplementation and have found promising results.

It is believed that vitamin D may prevent the onset of the disease by positively influencing gut health.

Additionally, it may alleviate disease progression thanks to its anti-inflammatory effect, which improves immune responses.

Here’s how vitamin D may affect ulcerative colitis, according to research.

It may improve intestinal barrier function

People with IBD have increased intestinal barrier permeability — meaning that the gut’s lining is compromised, allowing food and your gut’s friendly bacteria (or microbiota) to reach intestinal tissue.

That increases the immune system’s exposure to gut microbiota, which leads to a heightened and abnormal immune response associated with inflammation and increased disease severity.

Laboratory studies show that vitamin D is critical for maintaining intestinal barrier integrity. The vitamin helps regulate proteins that can revert gaps in intestinal tissues.

It may improve gut microbiota

Aside from improving gut tissue, vitamin D may also improve gut microbiota, which is strongly linked to IBD and colon cancer.

Unlike the general population, who have a relatively stable microbiota, the microbiota of people with ulcerative colitis varies more over time. A deficiency in vitamin D may alter microbial balance.

On the one hand, vitamin D deficiency has been associated with higher concentrations of Bacteroides species, which are believed to increase susceptibility to colitis — an inflammation of the lining of the colon — and weaken anti-inflammatory responses.

On the other hand, vitamin D deficiency is associated with lower concentrations of Lactobacillus species — the type of bacteria you usually find in probiotics — which, in contrast, helps relieve colitis.

Therefore, vitamin D supplementation may help rebalance the microbiota of people with ulcerative colitis, thus helping reduce inflammation.

It may reduce inflammatory immune responses

Research suggests that vitamin D may inhibit multiple pro-inflammatory pathways.

Firstly, it helps reduce oxidative stress by regulating oxidative stress-reducing proteins, leading to reduced inflammation. In contrast, vitamin D deficiency may worsen oxidative stress in people with obesity.

Oxidative stress is a pro-inflammatory state caused by an imbalance between free radicals and antioxidants, which facilitates the onset of multiple chronic diseases.

Secondly, studies have found a direct effect of vitamin D on white blood cells — namely T cells, which are some of your body’s defense cells. They eliminate disease-causing microorganisms.

According to research, T cells with low vitamin D levels promote higher concentrations of pro-inflammatory markers, grow more rapidly, and induce more severe colitis.

In contrast, animal studies show that treating T cells with vitamin D slowed their growth, reducing inflammation. Thus, vitamin D may adjust T cells from a pro-inflammatory to an anti-inflammatory immune response.

It may reduce the risk of colon cancer

Inflammation plays a fundamental role in the development of colon cancer.

Compared to the general population, people with IBD have an increased risk of developing colitis-associated colon cancer — especially if they have vitamin D deficiency or if their inflammation is not well-managed.

Evidence shows that since vitamin D plays a key role in reducing inflammation, it may help prevent colon cancer by reducing colon inflammation before tumors develop.

As mentioned before, low vitamin D levels in people with ulcerative colitis are associated with increased disease severity and a higher risk of relapse.

Still, evidence on whether vitamin D supplementation is beneficial is mixed.

On one hand, studies have found that vitamin D supplementation leads to reduced inflammation, disease activity, and symptoms, thus improving quality of life.

In addition, higher vitamin D levels have been linked to higher remission rates — which is why some experts suggest that people with ulcerative colitis who have vitamin D deficiency should receive supplementation, seeing that they are less likely to consume adequate amounts of the vitamin through foods.

But on the other hand, further research indicates that vitamin D supplementation in people with IBD is challenging because impaired nutrient absorption means that higher doses are needed. High doses could lead to vitamin D toxicity.

Vitamin D toxicity can lead to hypercalcemia — when calcium levels in your blood are too high — which may cause nausea, muscle weakness, pain, disordered brain function, dehydration, and kidney stones.

Therefore, while evidence on vitamin D supplementation for ulcerative colitis seems promising, more research is needed.

The recommended amount of vitamin D to consume per day — also known as the daily value (DV) — for healthy people is 20 mcg or 800 International Units (IU).

However, people with ulcerative colitis need a higher dose, which may vary depending on whether they are deficient or insufficient in the vitamin. Even so, an adequate and safe dose is still undetermined.

Some studies suggest that dosages between 1,000–2,000 IU per day can improve quality of life and are safe for people with mild deficiency. Once sufficient vitamin D levels are reached, an intake of 1,000 IU per day may be recommended for maintenance.

Yet, while some studies recommend that people with severe deficiency consume between 2,000–4,000 IU per day, others up the dosage to 1,800–10,000 IU per day.

Vitamin D supplementation has been shown to be safe for most people. Its most common side effects include nausea, headaches, dry mouth, upset stomach, drowsiness, and fatigue.

A note on choosing high quality supplements

While research suggests there are health benefits, the Food and Drug Administration doesn’t monitor or regulate the quality of supplements in the same way that it regulates clinical medications.

It’s important to talk with a healthcare professional before you begin using supplements and be sure to research the quality of a brand’s products.

Adding the following nutrients to your diet may help you manage ulcerative colitis:

  • Vitamin D-rich foods: Sources include oily fish, such as herring, mackerel, salmon, and sardines, as well as beef liver, egg yolks, and fortified milk products. Try adding some of these to your diet to increase your vitamin D intake.
  • Calcium: Experts suggest that people receiving steroids — a common treatment for ulcerative colitis — should increase their calcium intake because the drugs reduce calcium absorption from the gut, which may increase the risk of osteoporosis. Here are some foods that are high in calcium (including dairy-free options).
  • Iron, zinc, and vitamin B12: Levels of iron, zinc, and vitamin B12 are frequently low in people with IBD and should be monitored closely to avoid deficiencies.
  • Fiber: According to research, following a fiber-rich diet — namely from fruit sources — may protect against IBD development. Learn more about the link between fiber and ulcerative colitis here.
  • Omega-3 fatty acids: Adding omega-3 fatty acids to your diet may reduce flare-up periods or prolong remission duration due to their anti-inflammatory activity. Consider supplements or these food sources.
  • Low FODMAP diet: Following a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) can benefit some people with ulcerative colitis by decreasing abdominal pain, flatulence, and diarrhea. Be sure to work with a healthcare professional like a registered dietitian if you want to reduce your FODMAP intake, as a low FODMAP diet can be restrictive and lead to some nutrient deficiencies if not planned carefully.

On the contrary, high intakes of alcoholic beverages, high-fat foods, sweets, and artificial sweeteners may increase the risk and symptoms of ulcerative colitis.

Lastly, research suggests getting enough sunlight exposure is key to helping with your body’s vitamin D production. However, be sure to avoid excessive exposure, which may lead to the degradation of vitamin D and increase your risk of skin cancer.

Vitamin D is a fat-soluble vitamin that may play a key role in the prevention and management of ulcerative colitis.

According to research, vitamin D may benefit gut health and improve immune response through its anti-inflammatory activity.

In contrast, its deficiency may increase ulcerative colitis disease severity, hospitalization, need for surgery, and even cancer risk.

Nevertheless, evidence on whether vitamin D supplementation is beneficial is mixed, and an adequate and safe dose is yet to be determined. Be sure to talk with a healthcare professional before trying vitamin D to manage your symptoms.