Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review

Risks and benefits of omega-3 fatty acids on cancer risk

19 April 2006

Risks and benefits of omega-3 fatty acids on cancer risk

Editor - Hooper et al1 systematically reviewed cohort studies and randomized controlled trials to examine whether intake of omega-3 fatty acids (FAs) or n-3 polyunsaturated fatty acids (PUFAs) is beneficial for prevention of cardiovascular disease and cancer, and concluded that n-3 PUFAs have little effects for reducing the risk of cancer.

We here would like to discuss most frequently probed associations between consumption of n-3 PUFAs and risk of colorectal cancer. Seven articles cited as negative effects, except one, of n-3 PUFAs on colorectal carcinogenesis were reported from the USA (3 articles), Norway (2 articles), Sweden (1 article) and the Netherlands (1 article).1

Consumption of total FAs and saturated FAs seemed greater in those people than that in Japanese, but no differences for the intake of arachidonic acid (AA) and alpha-linolenic acid. Intake of highly unsaturated FAs (n-3 HUFAs) or fish FAs in Japanese, on the other hand, was far greater than those people, indicating that the consumption of n-3 HUFAs by those people is only approximately 1/10th of Japanese. Because n- 3 PUFAs compete with n-6 PUFAs (or AA) in various metabolic processes, the absolute intake of n-3 PUFAs (or n-3 HUFAs) may be crucial for colorectal carcinogenesis.2 Consumption of n-3 HUFAs in those people appears insufficient to exert pharmacologic influence.

The ratio of n-3 PUFAs/n-6 PUFAs (or specifically n-3 HUFAs/AA) may also be critical. The ratios in those people appear to be far less than those in Japanese. Plasma concentration of phospholipids in those people would be expected to be highly saturated with n-6 PUFAs, linoleic acid and AA, in particular, and the concentrations of n-3 PUFAs and n-3 HUFAs might not effectively compete in the arachidonate cascade.3

As seen in our observational study4 and randomized controlled trial,5 omega-3 FAs, n-3 PUFAs and/or n-3 HUFAs may indeed be favorable for the prevention of colorectal adenomas/tumors in populations, including Japanese, who consume appreciable amounts of fish and marine foods. (317 words)

Shinkan Tokudome,1 Masayo Kojima,1 Chiho Goto,2 Nahomi Imaeda,3 Yuko Tokudome,2 Kiyonori Kuriki,4 Sadao Suzuki,1 Hiromitsu Ichikawa,1 Ryosuke Ando,1 Nami Hattori,1 and Harumi Okuyama5

1Department of Health Promotion and Preventive Medicine, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan, 2School of Health and Human Life, Nagoya-bunri University, Inazawa, Japan, 3Faculty of Human Life and Environmental Sciences, Nagoya Women�fs University, Mizuho-ku, Nagoya, Japan, 4Division of Epidemiology and Prevention, Aichi Cancer Center Research Institute, Chikusa-ku, Nagoya, Japan, 5Kinjogakuin University College of Pharmacy, Moriyama-ku, Nagoya, Japan

References

1. Hooper L, Thompson RL, Harrison RA, Summerbell CD, Ness AR, Moore HJ, et al. Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review. BMJ, 2006; 332: 752 -60.

2. Nkondjock A, Shatenstein B, Maisonneuve P, Ghardirian P. Specific fatty acids and human colorectal cancer: an overview. Cancer Detect Prev, 2003; 27: 55-66.

3. Lands WEM, Libelt B, Morris A, Kramer NC, Prewitt TE, Bowen P, et al. Maintenance of lower proportions of (n-6) eicosanoid precursors in phospholipids of human plasma in response to added dietary (n-3) fatty acids. Biochim Biophys Acta, 1992; 1180: 147-62.

4. Kojima M, Wakai K, Tokudome S, Suzuki K, Tamakoshi K, Watanabe Y, et al. Serum levels of polyunsaturated fatty acids and risk of colorectal cancer: a prospective study. Am J Epidemiol, 2005; 161: 462-71.

5. Cheng JL, Ogawa K, Kuriki K, Yokoyama Y, Kamiya T, Seno K, et al. Increased intake of n-3 polyunsaturated fatty acids elevates the level of apoptosis in the normal sigmoid colon of patients polypectomized for adenomas/tumors. Cancer Lett, 2003; 193: 17-24.

Competing interests: None declared

Competing interests: None declared

Shinkan Tokudome, Professor

Masayo Kojima, Chiho Goto, Nahomi Imaeda, Yuko Tokudome, Kiyonori Kuriki, Sadao Suzuki, Hiromitsu Ichikawa, Ryosuke Ando, Nami Hattori, and Harumi Okuyama

Nagoya City University Graduate School of Medical Sciences, Mizuho-ku, Nagoya 467-8601, Japan

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