One point I've been making for a long time now involves the difficulty of determining exactly what is causative in the finding of "major studies." Today, a report appeared that explains one example of this problem (and thus the need to consider molecular-level evidence, not just statistical correlations):
QUOTE: Contrary to expectations, diets high in the nutrient choline were associated with an increased risk of some colorectal polyps, which can--but do not always--lead to colorectal cancer, according to a study published online in the August 7 Journal of the National Cancer Institute.
Major food sources of choline include red meat, eggs, poultry, and dairy products. Choline is involved in a biochemical process known as one-carbon metabolism. Studies have shown that people with increased intake of other nutrients required for one-carbon metabolism, such as folate, are at a decreased risk for colorectal polyps...
"Although our results were contrary to expectation based on choline's role [in one-carbon metabolism], there is a potential biologic basis for the positive association that we observed...Once a tumor is initiated, growth into a detectable [polyp] depends in part on choline availability because choline is needed to make membranes in all rapidly growing cells," the authors write. However, because this was the first study of choline and colorectal polyps, and other components of diets high in choline may be responsible for the association, the finding needs to be replicated in other studies.
In an accompanying editorial, Regina Ziegler, Ph.D., and Unhee Lim, Ph.D., of the National Cancer Institute in Bethesda, Md., describe the complexity of the relationship between one-carbon metabolism and the development of cancer.
"Clearly, one-carbon metabolism and its role in [cancer development] is more complicated than originally anticipated, and our understanding of the underlying mechanisms is probably incomplete... UNQUOTE.
Source: http://www.sciencedaily.com/releases/2007/08/070807172435.htm |
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