Vitamin D is essential in part because we need it to absorb calcium into our bones.
But the functions and benefits of this hormone-like nutrient range far and wide, with growing evidence linking higher vitamin D levels to better cardiovascular and immune health.
What about cancer?
During the 1940’s, researcher Frank Apperly discovered that cancer death rates were lower in sunnier southern latitudes, and higher in northern climes.
Vitamin D plays a key role in immunity, including inflammation, which is believed to promote colorectal cancer growth.
And because sun exposure triggers production of vitamin D, professor Apperly thought this might explain the statistical link between more sun and less cancer.
Since we started reporting on this topic back in 2007, growing evidence has linked higher blood levels of vitamin D to reduced rates of certain cancers — especially colon and breast tumors (you’ll find links to those reports at the end of this one).
In America, colorectal cancer accounts for about eight percent of new cancer cases annually and it’s the second-biggest cause of cancer death in the United States, behind lung cancer.
(In terms of annual cancer diagnoses, colorectal cancers come in fourth, behind breast, lung, and prostate cancers — but as the death statistics show, it’s deadlier than breast or prostate cancer.)
The U.S. National Institute of Health projects that in 2018, America will witness more than 140,000 new cases of colorectal cancer and more than 50,000 deaths.
And the American Cancer Society estimates that about 1 in 22 (4.49%) men and 1 in 24 (4.15%) women will develop colorectal cancer during their lifetime.
Seven years ago, Chinese researchers reviewed the evidence from nine epidemiological studies, and linked higher vitamin D levels with reduced colorectal cancer risk. As they wrote, “Vitamin D intake and blood levels were inversely associated with the risk of colorectal cancer in this meta-analysis.” (Ma Y et al. 2011)
Now, an even larger evidence review affirms hopes that higher blood levels of vitamin D can help prevent colorectal cancers.
New study reviewed the best epidemiological evidence
The new evidence review is the largest ever published, making its outcome worthy of close attention.
An international research team examined data from 17 epidemiological studies, looking for statistical links between vitamin D blood levels and the risk of colorectal cancer.
The evidence review was performed by researchers at the American Cancer Society, the National Institutes of Health, Emory University, Harvard Medical School, Boston University, Johns Hopkins University, and Italian cancer research centers.
Collectively, the 17 studies involved 5,706 colorectal cancer patients and 7,107 people who were free of colorectal cancer, and matched the patients for age, race, and date of blood draw (McCullough ML et al. 2018).
For consistency, all the blood was tested or re-tested using the same method at the same medical laboratory.
The participants were followed for an average of 5½ years, with the 17 studies ranging in length from 1-25 years.
Evidence review's results link vitamin D to reduced colorectal cancer risk
The new analysis strongly suggests that higher vitamin D levels reduced the risk of colorectal cancer.
In other words, the cancer-free people in the 17 studies had higher average vitamin D levels, compared with the colon cancer patients.
The authors of the new review also wanted to see how the seemingly protective vitamin D levels compared to those considered “adequate” by the National Academy of Medicine (NAM).
The lowest levels of cancer risk were found among people who had vitamin D levels higher than the NAM recommendation. However, there was a level beyond which the risk didn't drop any lower.
And the analysis showed that people with vitamin D levels below the NAM’s recommended level were 31% more likely to develop colorectal cancer.
The average lifetime risk of colorectal cancer is about 4%, so a 31% increase in risk raises the lifetime risk to a little above 5%.
Study leader Marjorie L. McCullough, ScD, RD of the American Cancer Society drew this conclusion: “What’s optimal for colorectal cancer may be different for what’s optimal for bone health.”
Although epidemiological studies cannot prove a cause-effect relationship between a nutrient and the risk for a disease, the results of the new review echo those of the prior studies listed below.
Vitamin D requirements
The recommended daily allowance (RDA) for people aged 1 to 70 is 600 IU. Children younger than age 1 should get 400 IU daily, and adults older than age 70 should get 800 IU per day.
When it raised the RDAs for vitamin D back in 2010, the Institute of Medicine set its recommended minimum blood level at 20 nanograms per milliliter (ng/mL).
However, leading vitamin D researchers recommend a minimum of 30 ng/mL or more, because levels at or above that are associated with lower risk of diverse diseases.
For example, leading vitamin D researcher Michael F. Holick, Ph.D., M.D., of Boston University Medical Center says the evidence supports the wisdom of vitamin D levels above 30 ng/mL and he says that levels up to 100 ng/mL are “perfectly safe” … unless you have an uncommon inflammatory disease called sarcoidosis.
And the results of the new evidence review seem to support his and other expert recommendation.
Vitamin D sources
You can get vitamin D from sunrays, foods, and/or supplements.
And get your vitamin D blood levels tested, so you know where you stand.
Excessive sun exposure — especially for people with fair skin — is a risk factor for skin cancer.
However, standard advice concerning sun exposure and use of sunscreens is controversial, because moderate sun exposure is linked to lower risk for cancer in general.
For more on that, see Sunscreen Advice Called Overkill and Cancer Society's Anti-Sun Ads Decried as Deceptive.
Diet can play a significant role in your body’s ability to fend off cancer-promoting DNA damage from UV sunrays — see Smart Eating to Discourage Sun Damage.
Fish fit the vitamin D bill; Sockeye salmon stand out
Certain fatty fish are the richest food sources of vitamin D, by far.
Among fish, wild sockeye salmon rank as the richest source, with a single 3.5 ounce serving surpassing the U.S. RDA of 600 IU:
Vitamin D per 3.5 ounce serving*
Ways to lower your risk for colorectal cancer
The available evidence supports the wisdom of simple lifestyle changes:
The same lifestyle habits can also reduce your risk for other major health threats, including heart disease and type 2 diabetes.
Learn more about vitamin D and cancer
You’ll find these and other articles in our newsletter archive: