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Long touted for its role in keeping bones strong — vitamin D also may be important in preventing colon cancer.
New research from the American Cancer Society and other public health groups finds people with higher than recommended blood levels of vitamin D have a lower risk of developing colorectal cancer. The finding was particularly significant for women.
The opposite may also be true: people with a vitamin D deficiency were found to have an increased risk for the disease.
The new research project combines data on more than 12,000 people in Europe, Asia and the U.S.
“Participants who had vitamin D levels that were higher than the recommended levels had a statistically significant 22 percent lower risk of colorectal cancer,” said Marjorie McCullough, senior scientific director at the American Cancer Society.
But some outside experts say more research is needed before doctors recommend vitamin D supplements specifically for colon cancer prevention.
Dr. Zhaoping Li, director at the UCLA Center for Human Nutrition, said the research is informative, but does not prove increasing vitamin D levels would prevent colon cancer. Instead, “this gives us a good reason to invest time and effort to see whether vitamin D can have an impact on colon cancer incidence,” said Li.
“This is not the smoking gun,” she said. Li was not involved with this latest American Cancer Society study.
Colorectal cancer is the third most common cancer and third leading cause of cancer-related deaths in the U.S. And there’s been a worrisome rise in the number of younger adults diagnosed with the disease.
That’s why the American Cancer Society recently lowered the recommended age to begin colorectal screening from 50 to age 45. It’s one of the few cancers that can be prevented with screening tools like colonoscopy.
But could vitamin D be another path to prevention? Dietary guidelines suggest most adults get at least 600 international units (IU) of vitamin D a day. This new research finds even larger amounts would offer stronger protection against colorectal cancer. However, study authors warn there’s a limit on the apparent benefit.
“It's worth noting that people who had the highest levels that we looked at did not continue to see a lower risk of colorectal cancer, so there does appear to be this sweet spot,” said McCullough.
It’s unclear where that sweet spot is, though.
True cancer prevention likely comes from multiple lifestyle changes: exercise, maintaining a healthy weight, not smoking and a healthy diet rich in fiber, as well as, yes, vitamin D.
Li almost always recommends at least 1,000 IU a day. She said there’s emerging evidence that vitamin D not only regulates calcium for bone health — it also may impact the immune system and cell growth.
Sunlight is the easiest way for the body to absorb D, but of course too much UV light can increase the risk for skin cancer. Experts say casual exposure to the sun — a short walk down the street or running to catch a bus, for example — is generally sufficient.
Vitamin D is also found in a few foods: cod liver oil, fatty fish like salmon, tuna, egg yolks and fortified cereal, milk and orange juice.
Experts aren’t suggesting everyone should rush to their doctors to get their vitamin D levels checked.
“People who are at higher risk of having lower levels are people who are never exposed to the sun, people who have dark skin who live in northern latitudes, and who don't eat the foods that are fortified by vitamin D and who don't like fatty fish,” said McCullough.
The American Cancer Society predicts more than 140,000 people will be diagnosed with colorectal cancer this year, and more than 50,000 will die from the disease.