Prediagnostic level of fatty acids in serum phospholipids: n-3 and n-6 fatty acids and the risk of prostate cancer

Ecological and case-control studies have demonstrated a positive correlation between consumption of fat and the risk of prostate cancer. Two recent human studies have focused on alpha-linolenic acid as a risk factor for prostate cancer. Animal experiments have shown that dietary n-6 polyunsaturated fatty acids have generally stimulated tumour development, whereas n-3 polyunsaturated fatty acids have diminished it. The aim of our study was to investigate the association between these fatty acids and the subsequent risk of prostate cancer. Blood donors to the Janus serum data bank in Norway, who later developed prostate cancer, were matched to blood donors without prostate cancer (141 matched sets); the proportional level of fatty acids measured before diagnosis in the donors� serum was examined. The risk of later prostate cancer was analysed by conditional logistic regression. Increasing risk for prostate cancer was found with increasing quartiles of palmitoleic, palmitic and alpha-linolenic acid. An inverse risk association was found with increasing levels of tetracosanoic acid, for the ratios of linoleic to alpha-linolenic acid and arachidonic to eicosapentaenoic acid. There was no clear association between the risk effect of total n-3 and total n-6 fatty acids. There were no indications of a relationship between fatty acids and more aggressive cancers. Our results verify recent findings of a positive association between alpha-linolenic acid and a negative association between the ratio of linoleic to alpha-linolenic acid and the risk of prostate cancer. (Author's abstract)
Ecological studies first demonstrated a correlation between consumption of fat and death from prostate cancer and case-control studies have added support to a positive association with dietary fat, particularly saturated and animal fat. The direct effect of n-3 FAs, including alpha-linolenic acid on cancer is not clear. Varying results in cohort and case-control studies on diet and prostate cancer may be attributed to difficulties in the proper recording of dietary data.  The aim of this study was to investigate the association between serum phospholipid FA levels, particularly the long-chain polyunsaturated n-3 and n-6 FAs (PUFAs), and the subsequent risk of prostate cancer. A positive association was found between both n-6 linoleic acid (LA) and alpha-linolenic acid (ALA) and prostate cancer.  Prostate cancer risk was positively associated with the saturated myristic and palmitic acids. Overall the findings  could not confirm the hypothesis that saturated fat may increase the risk of prostate cancer, and that unsaturated fat may reduce this risk. There was no association between deaths from prostate cancer and the various FAs.  Studies of dietary fat and cancer risk are necessary since much controversy in the results exist and little is known about causal mechanisms. (Editor's comments)