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

BMJ 2006; 332 doi: http://dx.doi.org/10.1136/bmj.38755.366331.2F (Published 30 March 2006) Cite this as: BMJ 2006;332:752

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

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: No competing interests

19 April 2006
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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