Vitamin D Levels Linked to Lower Colorectal Cancer Risk

A study by an international group of researchers from organizations including the American Cancer Society finds that higher levels of vitamin D in the blood is associated with a lower risk for getting colorectal cancer. Previous studies have suggested a link but were inconclusive. The new study was published online June 14, 2018 in the Journal of the National Cancer Institute.

The researchers combined data from 17 prospective studies, which is a type of study that follows people over time to try to determine why some of them get a certain disease, in this case colorectal cancer. The analysis is the largest to date, using data from about 12,800 people. All participants were tested for vitamin D levels in their blood before diagnosis. Often, this measure was taken when they initially joined the study. They became part of the new analysis because they developed colorectal cancer. Another group was matched to the study group by age, race and date of blood draw. These “matched” controls were people who did not have colorectal cancer. All the blood was tested or re-tested using the same method at the same medical laboratory for consistency.

The importance of vitamin D

Vitamin D has long been known to be needed for bone health. Participants in the study were considered to have enough levels of vitamin D in their blood if they met the National Academy of Medicine (NAM) suggested levels of circulating vitamin D based on evidence for maintaining healthy bones.

The study found that people with deficient serum vitamin D levels according to the NAM definition had a 31% higher risk of colorectal cancer during the length of time they were followed, which was an average of 5 ½ years (the full range was 1-25 years). The lowest colorectal cancer risk was found in people who had circulating vitamin D levels even higher than the NAM recommendation for sufficient concentrations. However, the risk did not continue to decrease for the very highest levels of vitamin D concentrations the study looked at.

According to Marji McCullough, ScD, RD, American Cancer Society epidemiologist and co-first author of the study, the findings indicate there may be a target range of circulating vitamin D levels that may be associated with lowest risk for colorectal cancer. She said, “What’s optimal for colorectal cancer may be different for what’s optimal for bone health.” In the US, laboratories often use different methods when measuring vitamin D status than were used in this study, and may have different definitions from NAM of how much is needed to be healthy.

However, these findings do not change current public health policy. “This large study can contribute to the evidence that is reviewed by scientific committees that determine nutrient recommendations,” said McCullough.

How to get vitamin D

People can get vitamin D from their diet, from supplements, and from the sun. However, staying out in the sun without protection exposes people to harmful UV rays, which is a strong risk factor for skin cancer. And getting too much vitamin D, for example, from taking very high doses of supplements, can be harmful. McCullough offers these tips:

• Include naturally vitamin-D-rich foods in your diet. These include fatty fish such as salmon, trout, sword fish, and tuna. Eggs and mushrooms also contain small amounts of vitamin D.
• Milk, including soy and almond milk, is fortified with Vitamin D. Some other dairy products, orange juice, and cereal also can have vitamin D added. Read labels to be sure.
• People ages 1 to 70 should get the recommended daily allowance (RDA) of 600 IU. Children younger than age 1 should get 400 IU and adults older than age 70 should get 800 IU.
• If you take a calcium supplement, you may already be getting added vitamin D. Many calcium supplements contain vitamin D.
• The study does not suggest that high dose supplements are needed and does not suggest that most people need to have their vitamin D levels checked. However, if you are concerned about your levels of vitamin D, check with your health care provider.
• Do not give up sunscreen or try other ways to get vitamin D from the sun. Sun exposure raises your risk for skin cancer.

How to lower your risk for colorectal cancer

McCullough points out there is already strong evidence that several important ways to lower the risk for colorectal cancer are to adopt certain lifestyle habits. They include:

• Maintaining a healthy body weight throughout life
• Staying physically active
• Limiting alcohol
• Not smoking
• Eating a healthy diet low in red meat and processed meat, and high in dietary fiber, including whole grains, vegetables, and fruits
• Following guidelines for colorectal cancer screening

Adopting healthy lifestyle habits can also lower your risk for other diseases including heart disease and type 2 diabetes.