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Colorectal cancer Patient friendly summary

 Colon cancer was the first cancer to be associated with lack of sunlight exposure and vitamin D deficiency. Image shows an artist's rendition of colon cancer progression.

Colorectal (large intestinal) cancer affects the colon, or bowel, and rectum. It is one of the most common types of cancers in Western developed countries. Each year in the United States, more than 140,000 people are diagnosed with colorectal cancer and around 50,000 die from the disease.

Risk factors

Important risk factors for colorectal cancer include:

  • Diets high in animal products
  • Smoking
  • Alcohol consumption
  • Being overweight

Fresh fruits and vegetables and whole grains may lower disease risk.

Sunlight exposure and colorectal cancer risk

As early as 1980, colon cancer was credited as the first cancer to benefit from sunlight. Early U.S. studies noted high death rates in the Northeast. This area has limited sunshine. Low mortality rates were noted in the Southwest, which has more sunshine. Many studies since then have confirmed these findings for both colon and rectal cancer. Ultraviolet-B (UVB) light produces vitamin D. Researchers concluded that vitamin D provides the primary cancer benefit.

Vitamin D and colorectal cancer

Vitamin D levels

There are numerous studies of the link between vitamin D and colorectal cancer rates. Such studies generally find that rates drop rapidly as vitamin D levels rise above 5-10 ng/mL (12-25 nmol/L), then more slowly until levels of 40 ng/mL (100 nmol/L) are reached. 

How vitamin D works

Vitamin D blocks the growth of cancer tumors. The active form of vitamin D, calcitriol, does most of the work. Calcitriol is made in the liver and in various organs affected by cancer. This form of vitamin D offers several benefits:

  • Activates vitamin D receptors, which turn genes on and off
  • Prevents cancer from starting (Calcitriol encourages cells to either adapt to their new organ or commit apoptosis [cell suicide].)
  • Keeps surface layers of organs intact
  • Limits blood supply to the tumor
  • Reduces the spread of cancer
  • Increases absorption of calcium from the intestines (Calcium may reduce the risk of colorectal cancer.)


Based on studies of colon and rectal cancer, vitamin D levels above 40 ng/mL (100 nmol/L) may reduce the risk of cancer. Taking 1000–4000 international units (IU) (25–100 mcg)/day of vitamin D may lower colorectal cancer risk.

Vitamin D and calcium

Studies have shown that taking both vitamin D and calcium provides additional cancer protection for many types of cancer. Calcium intake of more than 1000 mg/day from either diet or supplements is recommended.

Patients in one study took daily doses of 1100 IU (27.5 mcg) vitamin D and 1450 mg calcium. These patients had a 77% reduction in all-cancer rates between the ends of the first and fourth years of the study compared to those taking a placebo.


People with higher vitamin D levels at time of colorectal cancer diagnosis have better outcomes.

Harvard University studied patients with this cancer and vitamin D levels of about 25 ng/mL (63 nmol/L) or 31 ng/mL (78 nmol/L). Patients with higher vitamin D levels had half the death rates compared of those with lower vitamin D levels. A Japanese study found a similar effect for rectal cancer but not colon cancer.

Neither of these studies used vitamin D to treat colorectal cancer. However, vitamin D supplements may increase survival rates. Some cancer treatment centers are giving patients 5000 IU/day of vitamin D3 (cholecalciferol).

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 Colorectal cancer.

Page last edited: 07 September 2011