Fish is a problem topic. Like chicken, a lot of it is served deep-fried. There is also the complication of the sheer number of types of fish. Then there are the the distinctions of salt versus freshwater; fatty versus lean; farmed versus wild-caught; the waters they were caught in; the omega-3 content; cooking heat; how high up the foodchain the species is (which affects contaminant accumulation).
In some countries, such as Iceland, fish is an important part of the diet. In others, not so much. Also, available species differ geographically, so I have not thrown the studies together.
[1] U.S. studies. This might be a problem in that coastal regions presumably have a tradition of eating what is caught locally & that would vary significantly by region. On the other hand, a large part of the country does not have access to a fresh daily catch. Studies could easily be inconsistent, depending on where the participants live.
Men who eat more fish are presumably eating less meat. Fish eaters might have other potential risk modifiers (ref: [1c]).
Fish eaters might be more health conscious & more likely to have regular PSA tests (ref: [1d]). Ironically, this could undermine a study, since PCa detection increases with PSA screening.
Note that in countries, such as the U.S., where PCa levels are high, men who believe themselves to be at risk, e.g. because of familial PCa, might modify their diets well before any diagnosis. That would tend to undermine an association with protection too.
[1a] (2012 - California)
"We analyzed data for 1,096 controls, 717 localized and 1,140 advanced cases from the California Collaborative Prostate Cancer Study, a multiethnic, population-based case-control study. "
"We observed that high white fish intake was associated with increased risk of advanced PCA among men who cooked with high-temperature methods (pan-frying, oven-broiling and grilling) until fish was well done ..."
"No associations were found among men who cooked fish at low temperature and/or just until done ..."
It looks as though no association was found between fish consumption & PCa incidence. Nor for oily versus lean. Nor for white fish, dark fish & tuna, as categories.
[1b] (2010 - U.S. - CaPSURE)
Here is Erin Richman, the egg lady, with another part of that CaPSURE study.
{"CaPSURE™ is a longitudinal, observational study of approximately 15,000 men with all stages of biopsy-proven prostate cancer. Patients have enrolled at 43 community urology practices, academic medical centers, and VA hospitals throughout the United States since 1995."}
"Intakes of ... fish ... {was} not associated with prostate cancer recurrence or progression."
"Fish included canned tuna fish, dark-meat fish (salmon, mackerel, bluefish, swordfish, sardines, etc), other fish, and shrimp, lobster, or scallops as a main dish."
There is a serious problem with this study IMO - "Starting in 1995, men with biopsy-proven prostate cancer were invited to participate at 31 sites throughout the United States and asked to complete a questionnaire ..." We don't know how much fish they were getting before diagnosis.
[1c] (2008 - U.S. - Physician's Health Study)
Here is something better. A 22-year follow-up of 20,167 men who were free of cancer in 1983.
"During 382,144 person-years of follow-up, 2,161 men were diagnosed with prostate cancer and 230 died of prostate cancer. Fish intake was unrelated to prostate cancer incidence."
"... those consuming fish ≥5 times/wk had a 48% lower risk of prostate cancer death than did men consuming fish less than once weekly ..."
"A similar association was found between seafood {omega-3} fatty acid intake and prostate cancer mortality ..." A 36% risk reduction comparing the 20% of men having the highest consumption with the 20% having the lowest.
"At baseline, fish intake was positively related to the intake of tomato products and alcohol, the use of multivitamin and vitamin E supplements, and vigorous physical activity and was inversely related to the intake of whole milk and meats. Men with a high fish intake were more likely to be white and were less likely to be smokers."
[1d] (2003 - U.S. - Health Professionals Follow-up Study)
"We followed 47,882 men" for 12 years. "2,482 cases of prostate cancer were diagnosed, of which 617 were diagnosed as advanced prostate cancer including 278 metastatic prostate cancers"
"Eating fish more than three times per week was associated with a reduced risk of prostate cancer, and the strongest association was for metastatic cancer (multivariate relative risk, 0.56 ... compared with infrequent consumption, i.e., less than twice per month)."
"Intake of marine fatty acids from food showed a similar but weaker association. Each additional daily intake of 0.5 g of marine fatty acid from food was associated with a 24% decreased risk of metastatic cancer."
"Participants in the highest intake category of fish were more often users of multivitamin and fish oil supplements and were more often tested for PSA or had had a rectal exam than men in the lower intake categories."
"The associations for the individual fish dishes (canned tuna, fish with dark meat, and other, unspecified fish dishes) were weaker, and intake of seafood (shrimp, lobster, and scallops) was unassociated with risk of prostate cancer."
[1e] (2015 - U.S. - Physicians' Health Study)
"A total of 926 men ... diagnosed with nonmetastatic prostate cancer completed diet questionnaires for a median of 5.1 years after diagnosis, and were followed thereafter to assess mortality for a median of 9.9 years since questionnaire completion."
"Two post-diagnostic dietary patterns were identified: a Prudent pattern, characterized by higher intake of vegetables, fruits, fish, legumes, and whole grains; and a Western pattern, characterized by higher intake of processed and red meats, high-fat dairy and refined grains."
"During 8,093 person-years of follow-up, 333 men died, 56 (17%) of prostate cancer."
"Comparing men in the highest versus the lowest quartile of the Western pattern, the HRs {hazard ratios} were 2.53 ... for prostate cancer–specific mortality and 1.67 ... for all-cause mortality."
[1f] (2012 - U.S. - National Institutes of Health (NIH)-AARP Diet and Health Study)
Big study: "293,464 US men". "Between 1995 and 2006, we ascertained 23,453 incident cases of prostate cancer, including 2,251 advanced cases and 428 fatal cases."
"We examined the association between 3 diet quality indices—the Healthy Eating Index-2005 (HEI-2005), Alternate Healthy Eating Index-2010 (AHEI-2010), and alternate Mediterranean diet score (aMED)—and prostate cancer risk."
The aMED is the only one that captured fish intake.
"the fish component of aMED {was} inversely associated with fatal prostate cancer" 21% reduction in risk.
[2] Japan. A country with high fish intake & low PCa rates.
I came to the conclusion, some years ago, that I might have avoided much medical unpleasantness had I been the son of a Japanese fisherman.
A weakness of studies is the relatively small number of cases.
[2a] (2009 - Japan)
"We investigated the relationship between the intake of fish and the risk of death from prostate cancer."
"Fish consumption obtained from a baseline questionnaire was classified into the two categories of 'low intake' and 'high intake'. "
"Data for 5589 men aged 30-79 years were analysed." "... twenty-one prostate cancer deaths were observed during 75 072 person-years of follow-up."
High intake, versus low, was associated with an 88% less chance of dying from PCa.
[2b] (2004 - UK study of data from Hiroshima and Nagasaki)
"Subjects completed a food-frequency questionnaire at baseline (1963, 1965 and/or 1979) and were followed for incident prostate cancer until the end of 1996."
That's a long time without followup questionnaires.
Contrary to what one might have expected:
"men who consumed fish more than four times per week had a 54 increased risk of developing prostate cancer compared with men who ate fish less than twice per week"
Out of 18,115 men, only 196 cases in all that time.
[3] Sweden. A country with high fish intake & high PCa rates.
[3a] (2001 - Sweden)
"We studied the association between fish consumption and prostate cancer in a population-based prospective cohort of 6,272 Swedish men. During 30 years of follow-up, men who ate no fish had a two-fold to three-fold higher frequency of prostate cancer than those who ate moderate or high amounts did."
[4] Iceland. A country with high fish intake & high PCa rates.
[4a] (2013 - Iceland - the AGES-Reykjavik cohort study)
"Among the 2,268 men, we ascertained 214 prevalent and 133 incident prostate cancer cases, of which 63 had advanced disease."
"High fish consumption in early- and midlife was not associated with overall or advanced prostate cancer."
"Men consuming fish oil in later life had a {57%} lower risk of advanced prostate cancer"
"High intake of salted or smoked fish was associated with a 2-fold increased risk of advanced prostate cancer"
[5] UK.
[5a] (1996 - SW England)
Small study, included because the wording made me smile.
"... the central hypotheses for this study related to diet (fat and green vegetables), sexual activity and farming as an occupation."
"some statistically significant associations were found". "These included apparent protective effects of circumcision and high fish consumption." Both together?
...
I feel comfortable in saying that there is probably significant survival benefit from fish in the diet. I expect that to be true even in metastatic disease.
One thing I noticed when supermarkets in the U.S. put in fish counters 35+ years ago, is that the fish that sold well, was the type of fish that could be cooked like a steak. There are many ways to cook fish, but you wouldn't notice by ordering fish in a restaurant. An expensive piece of fish is likely to be slapped on the grill for a few minutes. Perhaps not the safest preparation.
It used to be that one bought fish intact. A quick inspection of the eyes, gills & skin would let one know if the fish was fresh. Even if the fishmonger fileted the fish, you could take home the head & backbone & make a quick stock for a tasty sauce. These days, most fish is 'conveniently' presented ready to cook. Head & skin are long gone. This has led to a lot of fraud at the distributer level. Sometimes, mislabeled fish is from an unrelated species. The mislabeling is always of a cheaper fish to a more expensive one.
There is fraud with farmed salmon. A sufficient number of people know that farmed salmon is inferior to the wild, that it has driven up the price of Alaskan salmon. The farms can easily manipulate the fat content via the feed, & the flesh color depends on pigments added to the feed. Once the fish is fileted, who can tell? The fraud itself happens at the distributor level. Retailers & restaurants are not skilled enough to spot the deception. & neither is the average customer.
The fraud is so widespread that I only buy Alaskan salmon in cans. The cans all have the odd shape that makes for nesting (when empty) & cheaper shipping to Alaska.
"Sardine" can be a meaningless term, but when the fish are baby herring, there is going to be a good omega-3 content. The fish are too far down the chain to have worrisome contaminants, IMO.
I don't touch canned tuna.
-Patrick
[1a] ncbi.nlm.nih.gov/pubmed/222...
[1b] ajcn.nutrition.org/content/...
[1c] ajcn.nutrition.org/content/...
[1d] cebp.aacrjournals.org/conte...
[1e] cancerpreventionresearch.aa...
[1f] aje.oxfordjournals.org/cont...
[2a] ncbi.nlm.nih.gov/pubmed/186...
[2b] ncbi.nlm.nih.gov/pubmed/155...
[3a] ncbi.nlm.nih.gov/pubmed/114...
