Study suggests fatty fish reduces women's kidney cancer risk
of fatty fish can help prevent the most common form of kidney
cancer in women, potentially providing yet another healthy point on
which to leverage sales of omega-3 products.
More than 80 per cent of all kidney cancers are accounted for by renal cell carcinoma (RCC). According to the charity Cancer Research UK, kidney cancer is the tenth most common form of the disease, with a male:female incidence ratio of 5:3. In the UK alone, around 6,600 new cases of kidney cancer are diagnosed each year, and the disease results in around 3,600 deaths.
Age, sex, obesity, smoking and several genetic and medical conditions are believed to be risk factors, but epidemiological data to support the role of diet in kidney cancer aetiology have yielded mixed results. In particular, a review of prospective cohort studies published in the Journal of the American Medical Association earlier this year (MacLean et al, JAMA 2006; 295:403-415) did not support the hypothesis that fish consumption exerts a protective influence.
But the authors of the new study, published in the same journal today (JAMA 2006, Vol 296, No 11), point out that most of the other studies on the subject, including MacLean's, did not split out fatty fish and lean fish, the former containing 20 to 30 times more omega-3 (DHA and EPA) than the latter, and three to five times more vitamin D.
Lead author Alicja Wolk and her co-investigators deemed fatty fish to be salmon, mackerel, sardines and herring. Lean fish were mainly cod, tuna and sweet water fish. Other seafood included shrimp, lobster and crab.
The researchers drew upon data gathered during the Swedish Mammography Cohort Study, which took place between March 1987 and December 1990. Of the 90,303 women who took part, 66,651 returned completed food frequency questionnaires at baseline.
A second questionnaire was sent out to the 56,030 participants who were still alive and residing in the area in September 1997, 39,664 of whom responded.
During the 15.3 years between 1997 and 2004, 150 cases of RCC were diagnosed amongst the women.
The researchers observed that those who consumed one or more serving of fatty fish each week seemed to have a 44 per cent decreased risk of RCC compared with those who consumed none at all.
Moreover, those who reported long-term consumption between baseline and the 10-year follow-up had a 74 per cent lower risk.
By contrast, no association was seen between lean fish and other seafood consumption and RCC incidence.
Wolk notes that per capita fatty fish consumption has been increasing in Sweden since the 1980s, with salmon-eating almost doubling and herring and other fatty fish by 50 per cent. Thus, the levels of consumption at follow up are more likely to give a true picture of current intake rates in the population.
"Our results support the hypothesis that frequent consumption of fatty fish may lower the risk of RCC possibly due to increased intake of fish oil rich in EPA and DHA, as well as vitamin D," wrote the researchers.
However, they added that that the results "require confirmation because this is the first epidemiological study addressing the issue."
