Analysis across 177 countries reinforces relationship between higher vitamin D levels and reduced cancer risk
by Craig Weatherby
Almost 30 years ago, University of California professor Cedric Garland—and brother Frank Garland of the the Naval Health Research Center—published landmark research linking reduced cancer risk to greater exposure to the sun, whose UV rays produce vitamin D in skin cells.
After decades of neglect by the biomedical community, a steady stream of striking epidemiological findings by the Garland brothers and others finally triggered a flood of research.
And the uniformly positive results published in recent years support vitamin D’s cancer-prevention potential very persuasively.
(Fish are the best food sources of vitamin D. And Sockeye Salmon ranks as the richest food source by far, with a 3.5 oz serving providing more than the US RDA of 400 IU and six times more than a glass of D-fortified milk; see "Fish Fit the Bill", below.)
Peruse our coverage of this topic by searching our newsletter archive for “vitamin D”, and see the related article in this issue about the common vitamin D deficiency in pregnant women and the serious risks it may pose (“Pregnancy Danger Linked to Low Vitamin D Levels”).
Now the Garlands have published what appears to be the first analysis that demonstrates and details a strong “dose-response” relationship between higher vitamin D blood levels and reduced cancer risk.
The analytical team included three other leading lights of vitamin D research: epidemiologists Edward Gorham, PhD and Sharif Mohr, MPH of San Diego’s Naval Health Research Center and former NASA scientist William Grant, PhD, who founded SUNARC: the Sunlight, Nutrition and Health Research Center in San Francisco.
Novel analysis defines anti-cancer power of vitamin D
The Garland team compiled data from observational studies, in which researchers follow a group of people over time recording their diets, lifestyles, and rates of disease. And they cherry-picked studies in which blood tests had been performed over time.
This freed the analysis from the usual pitfall of observational studies: reliance on people’s unreliable memories—of how much sun exposure they got or how much of every vitamin-D food source they ate—and the very crude estimates researchers must make based on these shaky memories.
Fish Fit the Vitamin D Bill; Sockeye Salmon Stand Out
Certain fish rank among the very few substantial food sources of vitamin D.
Among fish, wild sockeye salmon may be the richest source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent:
Vitamin D per 3.5 ounce serving*
Sockeye salmon—687 IU
Albacore tuna—544 IU
Silver salmon—430 IU
King salmon—236 IU
*For our full test results, click here.
As expected, the results showed that the people with the highest vitamin D levels had the lowest risk. And the relationship was linear, demonstrating the classic dose response that indicates, persuasively, the kind of cause-and-effect relationship hard to confirm from standard observational studies.
The findings confirm what well-informed public health researchers long ago concluded: that people do not consume enough vitamin D.
Scientists familiar with the research say that at minimum, we should double the US recommended daily allowance from 400 international units (IU) to 800 IU, and many support an RDA of 1,000 IU to 2,000 IU.
The study's projections indicate that in North America, colon cancer rates would be cut in half if people consumed 2,000 IU per day, and that breast cancer rates would be cut in half were women to consume 3,500 IU per day: amounts considered completely safe.
As the authors noted, citing recent research in this area, “…[there is] no established adverse effect of vitamin D3 intake below 10,000 IU [per day].”
Chronic vitamin D deficiency is usually linked to indoor occupations and lifestyles or living at latitudes located substantially north of the Mason-Dixon line.
People in Canada and northerly regions of America, Russia, and Europe usually display very low levels of vitamin D, because most of the vitamin D in our bodies stems not from foods—very few of which are substantial sources—but when sunlight strikes our skin.
Low vitamin D levels are decidedly dangerous, as they raise the risk of osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases, and cardiovascular diseases.
According to the Garland group’s analysis, the average American adult consumes only 230 IU per day, versus the widely (if not yet officially) recommended 2,000 IU per day.
In addition, they called into question the type of vitamin D used: “Use of ergocalciferol (vitamin D2), which is popular in Europe and is used in some major US brands of multivitamins, should be discontinued immediately in favor of vitamin D3.”
Vitamin D3 (cholecalciferol)—the most “bio-active” form—is produced in skin exposed to UVB radiation and is found in animal foods, primarily fatty fish and especially wild Sockeye Salmon. Vitamin D2 (ergocalciferol) is derived from plants and is less effective in the body.
For 177 countries, the Garland group obtained cancer-rate estimates, vitamin D blood levels, and data on the amount of wintertime ultraviolet B sunrays.
The scientists calculated that if people needing more vitamin D adopted their recommendations, it would raise their blood levels to 55 ng/ml or more.
And this rise, the analysis showed, would prevent at least 60,000 cases of colorectal cancer and 85,000 cases of breast cancer every year in North America alone.
- Garland CF, Grant WB, Mohr SB, Gorham ED, Garland FC. What is the dose-response relationship between vitamin D and cancer risk? Nutrition Reviews 65;8 (Suppl):91-95.
- Garland CF, Gorham ED, Mohr SB, Grant WB, Giovannucci EL, Lipkin M, Newmark H, Holick MF, Garland FC. Vitamin D and prevention of breast cancer: pooled analysis. J Steroid Biochem Mol Biol. 2007 Mar;103(3-5):708-11.
- Gorham ED, Garland CF, Garland FC, Grant WB, Mohr SB, Lipkin M, Newmark HL, Giovannucci E, Wei M, Holick MF. Optimal vitamin D status for colorectal cancer prevention: a quantitative meta analysis. Am J Prev Med. 2007 Mar;32(3):210-6.
- Gorham ED, Garland CF, Garland FC, Grant WB, Mohr SB, Lipkin M, Newmark HL, Giovannucci E, Wei M, Holick MF. Vitamin D and prevention of colorectal cancer. J Steroid Biochem Mol Biol. 2005 Oct;97(1-2):179-94. Epub 2005 Oct 19.