Inflammatory bowel diseasePatient friendly summary

  • UVB light from the sun is associated with lower risk of Crohn's disease and possibly Ulcerative colitis.
  • Vitamin D may reduce the risk of Crohn's disease and possibly Ulcerative colitis.

There are two forms of inflammatory bowel disease (IBD):

  • Crohn's disease (CD)
  • Ulcerative colitis (UC)
CD is an inflammatory immune disease of the intestinal tract. It causes thickening of the intestinal wall and inflammation of the intestinal lining (mucous membranes). Symptoms include abdominal pain, diarrhea, fever, and weight loss.

UC is a chronic inflammation of the colon that produces ulcers in its lining. This condition is marked by abdominal pain and cramps. UC also causes loose bowel discharges of pus, blood, and mucus.

Risk factors

Risk factors of IBD include some components of the Western diet:

  • Animal protein from meat and fish
  • Animal fat
  • Dairy products
  • Sugar

These dietary components interact with and alter the microflora in the gut. There is increasing evidence that the type of microflora may play a role in risk of IBD.

Sunlight exposure and IBD risk

International researchers have studied sunlight exposure and IBD risk:

  • European studies reported higher rates of IBD in areas of higher latitude. Countries farther from the equator have less sunlight and ultraviolet-B (UVB) radiation. The latitudinal effect is stronger for CD than UC.
  • In the United States, rates for CD and UC are highest in the Northeast. In this location, summertime solar UVB doses are lowest. Low solar UVB was linked more strongly to CD than to UC.
  • A study from India reported lower vitamin D levels in those with CD and lower sun exposure.

These studies suggest that vitamin D may reduce the risk of CD. The evidence is less clear for UC.

Vitamin D and IBD

Vitamin D levels

People with CD often have low vitamin D blood levels. The lower levels may contribute in part to CD. However, CD may also reduce vitamin D absorption from food.

How vitamin D works

Vitamin D lowers the risk of CD by:

  • Reducing inflammation
  • Maintains a strong mucosal barrier (lining of the intestines)


Studies in varied locations (Europe and the United States) came to similar conclusions. Higher vitamin D levels may reduce the risk of CD and possibly UC. Based on findings for other diseases, Vitamin D levels above 40 ng/mL (100 nmol/L) may provide a good protection.

Vitamin D and calcium

People with CD and low vitamin D levels have an increased risk for osteoporosis. These people should consider taking vitamin D and calcium.


In one study, people who took 1200 international units (IU) (30 mcg)/day of vitamin D3 (cholecalciferol) had half as many CD relapses as those taking a placebo. Vitamin D3 is the form of vitamin D produced by the skin.

IBD is sometimes treated with drugs known as thiopurines. This drug carries a small risk of nonmelanoma skin cancer. People who take thiopurines and want to increase their vitamin D levels should consider using supplements rather than UVB radiation. If choosing UVB light, expose as much of the body as possible for a short period of time. Mid-day sun is best.

Find out more...

Do you want to find out more and see the research upon which this summary is based?  Read our detailed evidence summary on Inflammatory bowel disease.

Page last edited: 06 May 2011