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 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.
