Colon cancer risk varies with different fatty acids
High plasma levels of the essential polyunsaturated fatty acids (PUFAs) linoleic and α-linolenic acids and the monounsaturated FA (MUFA) oleic acid are associated with a lower risk of colon cancer, while the reverse is seen for increased synthesis of arachidonic acid (an omega-6 PUFA), according to data from the Singapore Chinese Health Study (SCHS).
In a nested case-control study of the SCHS, 350 cases with colorectal cancers (211 colon cancer and 139 rectal cancer) were matched to equal number of control subjects by age, sex, dialect group, and date of biospecimen collection (for testing plasma levels of FAs). [NPJ Precis Oncol 2017;doi:10.1038/s41698-017-0040-z]
With increasing plasma levels of linoleic and α-linolenic acids, the risk of colon cancer decreases ─ the overall risk was more than halved with the highest quartile levels of the essential PUFAs (odds ratio [OR], 0.43; ptrend=0.008 for linoleic acid and OR, 0.41; ptrend=0.005 for α-linolenic acids).
Similarly, the risk of colon cancer was significantly lower with increasing levels of the saturated FA palmitic acid (OR, 0.41; ptrend=0.008 for the highest quartile) and the MUFA oleic acid (OR, 0.39; ptrend=0.015 for the highest quartile).
Increased activity of stearoyl-coenzyme A desaturase-1, an enzyme for oleic acid synthesis was also associated with a decreased risk of colon cancer, as indicated by the oleic:stearic acid ratio (OR, 0.42; ptrend=0.024).
The researchers believed that the mechanisms underlying the associations between FAs and colon cancer risk include modulation of inflammation, immunity, and cell signalling by the various FAs. “Our finding supports an alternative role of the essential omega-3 PUFA α-linolenic acid against the development of colon cancer by reducing inflammation and inhibiting proliferation and invasion … [as well as] a potential preventive role for the essential omega-6 PUFA linoleic acid in colon carcinogenesis that may be due in part to its effect on increasing apoptosis and decreasing cancer cell proliferation,” they said.
Conversely, increased synthesis of arachidonic acid, as reflected by the arachidonic:linoleic acid ratio, was positively associated with a more than threefold higher risk of colon cancer (OR, 3.53; ptrend=0.006). This association became particularly prominent among individuals who did not use NSAIDs regularly*.
According to the authors, arachidonic acid has been associated with colon carcinogenesis in previous studies as it is a known precursor of proinflammatory eicosanoids.
No association was found between FAs and rectal cancer risk.
“Our study is the first to demonstrate that risk associations with plasma FAs and their desaturase indices for colon cancer are different from those for rectal cancer,” said the researchers.
If confirmed, the findings that colon cancer risk differs with different FAs may “have implications for colon cancer prevention,” they noted.
“Plasma essential FAs reflect dietary intake. The primary dietary sources for α-linolenic acid are flaxseed, walnuts, and canola and soybean oils; and for linoleic acid, soybean, corn, and safflower oils, as well as nuts (ie, pine nuts, pecans, brazil nuts), and sunflower seeds,” the researchers added.