Large study compared people’s vitamin D levels and cancer rates: No reduction seen for other cancers, but experts note limitations and call for more study
by Craig Weatherby
The results of a large study suggest that the “seafood and sunshine” vitamin may reduce the risk of colorectal (colon) cancers by about 72 percent.
As researchers from Harvard University wrote last year in the Journal of the National Cancer Institute, “Vitamin D has potent anticancer properties, especially against digestive-system cancers” (Giovannucci E et al 2006).
Most media reports focused on the new study’s failure to find any association between higher blood levels of vitamin D and lower risk of non-colorectal cancers.
But the authors of an editorial accompanying the study emphasized that it may take longer than the six to 12 years during which people were followed in the new study to see the benefits of higher vitamin D levels, because it can take many years for a cancer to develop.
The editorialists also noted that it would have been better had the authors taken blood samples at several times, to better reflect the participants’ average vitamin D levels over time.
And in their rush to accentuate the negative, most news reports downplayed the study’s finding that higher vitamin D levels cut colon cancer risk dramatically.
Colorectal tumors are one of the leading causes of cancer-related deaths in the United States. The National Cancer Institute estimates there will have been 53,760 new cases of colorectal cancer, and 52,180 deaths from colorectal cancer in 2007.
(In most cases, early diagnosis can lead to a complete cure.)
Study finds vitamin D drops colon risk dramatically
The report, from the National Cancer Institute (NCI) and the Centers for Disease Control and Prevention (CDC), concluded that vitamin D levels in the participants’ blood were not related to overall cancer mortality.
However, the study did find that higher levels of vitamin D were associated with a substantial, 72-percent decrease in the risk of dying from colorectal cancer, and possibly with a reduction in the risk of dying from breast cancer.
It is well worth quoting these cogent comments made by J. Leonard Lichtenfeld, MD, FACP, Deputy Chief Medical Officer for the national office of the American Cancer Society (Lichtenfeld JL 2007):
- “Many other studies that have been reported to show a decrease in cancer deaths related to higher vitamin D intake or sun exposure have been done by excellent researchers from highly regarded institutions.”
- “…in this JNCI study, the numbers of certain cancer deaths may have been too small to reach an accurate conclusion. Or, perhaps the follow-up wasn’t long enough, or perhaps the impact of vitamin D would have been greater if the blood test had been performed in younger people who were then followed for many more years.”
- “…I have transitioned from being a skeptic to believing there may in fact be a role of vitamin D in reducing the risks of a variety of cancers… I can’t ignore the weight of that evidence suggesting that such a relationship exists.”
The NCI/CDC team analyzed vitamin D levels in almost 17,000 people participating in the Third National Health and Nutrition Examination Survey (NHANES), which collects raw data on Americans’ diets and health status in order to permit analyses like this one.
About 10 years after enrolling, 536 participants had died of cancer. Statistical analysis found no relationship between their vitamin D levels and their risk of dying from cancer in general.
But the analysis did reveal that people with blood levels above 80 nmol/L (nano moles per liter) were 72 percent less likely to have developed colorectal cancer, compared with participants whose vitamin D blood levels were substantially lower (i.e., less than 50 nmol/L).
It seems significant that vitamin D experts believe that optimal blood level of vitamin D is about 125 nmol/L: a level substantially higher than the 80 nmol/L associated with reduced risk of colorectal cancer in the new NCI/CDC study.
(Average adult vitamin D blood levels in the US range from 50 to 90 nmol/L, and vary widely by season, lifestyle, and state.)
Sunrays are the primary source of vitamin D for most people. The best food sources of vitamin D are oily fish (especially wild salmon; see sidebar above), with fortified dairy foods providing far less.
- Freedman DM, Looker AC, Chang SC, Graubard BI. Prospective Study of Serum Vitamin D and Cancer Mortality in the United States. J Natl Cancer Inst. 2007 Oct 30; [Epub ahead of print]
- Giovannucci E, Liu Y, Rimm EB, Hollis BW, Fuchs CS, Stampfer MJ, Willett WC. Prospective study of predictors of vitamin D status and cancer incidence and mortality in men. J Natl Cancer Inst. 2006 Apr 5;98(7):451-9.
- Lichtenfeld JL. Maybe Vitamin D Isn't The Answer After All. Accessed online November 2, 2007 at http://www.cancer.org/aspx/blog/Comments.aspx?id=174
- Scragg R, Sowers M, Bell C; Third National Health and Nutrition Examination Survey. Serum 25-hydroxyvitamin D, diabetes, and ethnicity in the Third National Health and Nutrition Examination Survey. Diabetes Care. 2004 Dec;27(12):2813-8.
- Grant WB, Garland CF, Gorham ED. An estimate of cancer mortality rate reductions in Europe and the US with 1,000 IU of oral vitamin D per day. Recent Results Cancer Res. 2007;174:225-34. Review.