RESEARCH - Eating fatty fish may cut women's kidney cancer risk

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Medpage Today

" Eating Fatty Fish May Cut Women's Kidney Cancer Risk " :

STOCKHOLM, Sept. 19 -- Dining on fatty fish at least once a week lowered

women's risk of renal cell carcinoma, but lean fish and the shrimp-lobster

tribe offered no such benefit, found researchers here.

A preliminary study found that women who consumed one or more servings of

fatty cold-water fish per week during an average of 15.3 years had a

statistically significant 44% decreased risk of renal cell carcinoma

compared with women who eschewed fish, according to a report in the Sept. 20

issue of the Journal of the American Medical Association.

For a subset of women with consistent long-term consumption of fatty fish at

baseline and 10 years later (one to three servings a month or more), the

risk was down 74%, said Alicja Wolk, D.M. Sc., of the Karolinska Institute,

and colleagues.

However, consumption of lean fish was not significantly associated with the

risk of kidney cancer in any of the follow-up periods, the researchers said.

Fatty fish included salmon, herring, sardines, and mackerel. Lean fish

included mainly cod, tuna, and sweet-water fish, as well as seafood such as

shrimp, lobster, and crayfish.

The findings came from the Swedish Mammography Cohort, a population-based

prospective cohort study of 61,433 women, ages 40 to 76, without a previous

diagnosis of cancer at baseline (March 1, 1987 to Dec. 14, 1990).

Participants filled out a 67-item food-frequency questionnaire at baseline

and in September 1997.

During 940,357 person-years of follow-up, there were 150 incident cases of

renal cell carcinoma. After adjustment for potential confounders, the

researchers found an inverse association of fatty fish consumption with the

risk of kidney cancer (P for trend=.02), but no association with lean fish

consumption.

Compared with no consumption, the multivariate rate ratio (RR) was 0.56 (95%

confidence interval 0.35-0.91) for women eating fatty fish once a week or

more.

For a subset of 36,664 women who filled out the baseline and the 1997

questionnaires, the RR was 0.26 (CI, 0.10-0.67) for women reporting

consistent consumption of fatty fish versus women who ate no fish. There

were 40 incident renal cell carcinoma cases during the 1998 to 2004

follow-up, the researchers reported.

On the other hand, the researchers said, there was no statistically

significant association with lean fish or other seafood (multivariate rate

ratio [RR], 0.71, 95% CI, 0.34-1.47) for one or more servings per week

versus no consumption. Exclusion of the first two years of follow-up did not

change the results.

No previous study has investigated the association between fatty fish and

lean fish specifically and the risk for renal cell carcinoma, Dr. Wolk said.

Previous studies of kidney cancer risk and fish consumption have had

inconsistent results and have analyzed total fish consumption not taking

into account the large differences between lean and fatty fish in the

content of omega-3 fatty acids and vitamin D, she added.

Compared with lean fish, fatty cold-water fish have up to a 20- to 30-times

higher content of marine omega-3 polyunsaturated fatty acid,

eicosapentaenoic acid, and docosahexanoic acid, all of which have been

reported to slow cancer development.

Also, the vitamin D levels in fatty fish are three to five times higher than

in lean fish, while lower serum vitamin D levels have also been linked to

the development and progression of renal cell carcinoma, the researchers

wrote.

The consumption of fatty fish in Sweden has been increasing since the

baseline time of this cohort, the researchers wrote. The consumption of

salmon, the main fatty fish, almost doubled, and the consumption of canned

herring and other fatty fish increased by 50% during the follow-up period.

Thus, the consumption of fatty fish during the two study periods may be

greater than that reported in this study, they said.

Several molecular mechanisms have been proposed for the effect of marine

fatty acids on carcinogenesis. The best known is ascribed to suppression of

arachidonic acid-derived eicosanoid biosynthesis, leading to an altered

immune response of cancer cells and modulation of inflammation, cell

proliferation, apoptosis, and angiogenesis, the researchers wrote.

As for the role of vitamin D, the researchers suggested that low serum

levels of vitamin D3, plentiful in fatty fish, may influence the development

and progression of renal cell carcinoma. Vitamin D3 exerts its biological

activity by binding to the vitamin D receptors, which are present in kidney

cells. The vitamin D receptor genotype, they said, may play an important

role in determining the risk of developing more aggressive kidney cancer.

Turning to the study's limitations, the researchers noted that the

self-administered questionnaire may have misclassified several types of

fish. Because of the observational nature of the study, it is possible, they

said, that an unevaluated risk factor for renal cell carcinoma, correlated

with fatty fish consumption, had some effect on the results.

Another limitation, they said is that because they did not analyze the

omega-3 fatty acids and vitamin D intakes directly, the explanation of the

observed results is based on speculation.

They concluded, " Our results, however, require confirmation because this is

the first epidemiological study addressing this issue. "

Primary source: Journal of the American Medical Association

Source reference:

Wolk, A. et al, " Long-term Fatty Fish Consumption and Renal Cell Carcinoma

Incidence in Women " JAMA 2006; 296:1371-1376.

http://www.medpagetoday.com/Nephrology/GeneralNephrology/tb/4142

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