Study Shows No Connection Between Vitamin D And Reduced Overall Cancer Deaths
October 31, 2007
No relationship was found between vitamin D levels and the overall risk of dying from cancer, according to a study published online October 30 in the Journal of the National Cancer Institute. However, higher vitamin D levels were associated with a decreased risk of colorectal cancer death.
Several epidemiological studies have supported the hypothesis that that vitamin D can reduce cancer mortality by decreasing cancer incidence or improving survival. Animal and cell studies suggest that vitamin D may reduce tumor growth and induce cancer cell death. Diet and exposure to sunlight are the major sources of vitamin D.
D. Michal Freedman, Ph.D., of the National Cancer Institute in Bethesda, Md., and colleagues analyzed data from the third national Health and Nutrition Examination Survey to examine the relationship between levels of circulating vitamin D in the blood and cancer mortality in a group of 16,818 participants aged 17 and older.
After about a decade of follow-up, 536 participants had died of cancer. Cancer mortality was not related to the level of circulating vitamin D for the overall group, nor was it related when the researchers looked at the data by sex, race, or age. But higher levels of vitamin D (80 nmol/L or more) were associated with a 72 percent reduced risk of colorectal cancer mortality, compared with lower levels (less than 50 nmol/L).
“To our knowledge, this study is the first to examine the relationship between measured serum vitamin D levels and cancer mortality for selected site and for all sites combined,” the authors write.
In an accompanying editorial, Cindy Davis, Ph.D., and Johanna Dwyer, D.Sc. of the National Institutes of Health in Bethesda, Md., discuss the complicated relationship between nutrients, like vitamin D, and cancer. They suggest that not enough is known about the benefits and limitations of vitamin D to use it for the prevention of disease or death.
“These findings must be put into the context of total diet and lifestyle. There are many risk factors other than diet for colorectal cancer, and there are many possible dietary risk factors other than vitamin D that have been linked to cancer risk,” the editorialists write.
Source: Journal of the National Cancer Institute
This study is of limited quality. The major weakness is that they followed the subjects for approx. 10yrs but only measured vitamin D levels (25OHD) once, at baseline. Vitamin D levels could have changed over ten years depending on diet, vacations, change in job, supplement use…etc.
This study took one blood sample only in the Southern latitudes it was taken in the cooler months and in the Northern latitudes in the warmer months.
In the UK Summer status averages 70nmol/L Winter status 40nmol/l.
Comparing winter status in southern latitudes with summer status in northern latitudes is bound to blur the differences.
We know that when cancer is diagnosed and treated in winter-late spring prognosis is worse than when similar breast/prostate/lung/colon cancers are diagnosed and treated Summer-Autumn when vitamin D status is higher.
If we want to compare cancer rates for different vitamin D status groups then we must compare like with like.
We should take blood at the same time at the different latitudes and we should ideally have 4 tests for each individual through the year so we know just how low the vitamin D status dropped.
If we were comparing road accidents and driving speed, would one observation of your driving speed be indicative of your driving speed over the following ten years and an accurate measure of your accident propensity?
Would it be fair to compare the driving speeds recorded on one occasion in summer in the north with those observed on one occasion in the south in winter?