Vitamin D and Colorectal Cancer

Posted on Monday, March 05, 2007
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More Vitamin D Lowers Risk of Colorectal Cancer – and Second Primary Cancers: Data indicate potential benefits, few dangers by Jeni Baker, Cancer Monthly Staff Writer

It is no secret that vitamin D promotes healthy bones and teeth, but did you know that it also can reduce your risk of developing a disease that struck more than 145,000 Americans in 2005*?

A team from the University of California San Diego reviewed data from five studies and has published its findings in the American Journal of Preventive Medicine**. The findings – as well as the most recommended preventive measure – might surprise you.

Revisited data reveal a connection

The five studies – conducted between 1966 and 2005 – each sought to identify a long-suspected relationship between vitamin D and colorectal cancer. To do this, researchers measured the serum 25 (OH)D levels of 1,448 total participants, who were tracked for between two and 25 years.

(Serum 25 (OH)D is the primary vitamin D compound found in the bloodstream, and the test for it is regarded as the most accurate clinical indicator of someone’s overall vitamin D status.)

The original studies revealed trends indicating a benefit of vitamin D, but no study was definitive. By combining the original data, the San Diego researchers strengthened its statistical reliability, and confirmed definitively that a high level of vitamin D in the blood is linked to a substantially lower risk of colorectal cancer.

Participants with serum 25 (OH)D levels of at least 33 nanograms per milliliter (ng/mL) had a 50 percent lower risk of developing colorectal cancer than people with levels at or below 12 ng/mL. In other words, the evidence suggests not only a relationship between vitamin D and colorectal cancer, but also that by increasing their vitamin D intake, people can reduce their odds of getting the disease.

The sunny side of the street

Although there are different ways people get vitamin D – vitamin supplements and diet, for example – the most effective way in terms of cancer prevention is to spend a little time in the sun, says co-author Cedric F. Garland, DPH.

Sun exposure allows our bodies to make vitamin D, which seems to be the reason behind higher colorectal cancer rates in places that see little sunshine. There’s an important distinction to make, however.

Vitamin D3 (cholecalciferol), what our bodies produce when we're exposed to sunlight, is the kind shown to help prevent colorectal cancer, Garland says. D3 is also present in most milk and some foods. Vitamin D2 (ergocalciferol) – which we get from many multivitamins and vitamin D supplements – is only one-fifth as effective as D3 at staving off the disease. Almost no foods naturally contain D2, although it is sometimes added to them.

Exercise moderation when heading out in the sun, however. People with different levels of skin pigmentation require different sun exposure times to reap the same benefits. And, Garland says, “people with skin cancer and diseases causing undue sensitivity to the sun are of course excluded from this recommendation.”

Cancer patients also see D3 gains

Vitamin D3 has significant additional benefits, as well, even for those already living with colorectal and other cancers (with the exception of non-melanoma skin cancer).

“Most cancer patients need about 2,000 IU of vitamin D3 per day, unless there are contraindications – the main one being a high serum calcium level that is sometimes present in advanced cancer,” Garland says. That level, established as the “no adverse effect level” by the Institute of Medicine “will help prevent a second primary malignancy and promote faster wound healing for patients who require surgery.”

Colorectal cancer patients, as well as those at risk for the disease, should speak with their doctors about regular serum 25 (OH)D screening – if for no other reason than trying to prevent the cancer’s spread or development another colorectal malignancy.

“The 25 (OH)D level is one of the most important data points to have, since 25(OH)D may influence your risk of metastasis – and it makes it easy to address a vitamin D deficiency with the appropriate amount of vitamin D3,” says Garland, adding a helpful hint:

If your insurance doesn’t cover the test, it may pay for one to determine your serum calcium level. Although that test is not useful for determining your current vitamin D status, a moderate intake of vitamin D3 is likely to be beneficial for you if your serum calcium is within the normal range."

Speak with your doctor about getting the dosage of vitamin D that’s right for you.

* The American Cancer Society
** Gorham ED, et al., Optimal Vitamin D Status for Colorectal Cancer Prevention (A Quantitative Meta Analysis). Am J Prev Med. 2007 Mar; 32(3):210-6.