Eating lots of fish may not protect men from developing prostate cancer, but it could reduce their risk of dying from the disease, a new review of the medical literature suggests.

"In the United States, one in six men will be diagnosed with prostate cancer over their lifetime," Dr. Konrad M. Szymanski of McGill University Health Center in Montreal, one of the study's authors, told Reuters Health. "One in six of these men will die of prostate cancer. Our study findings suggest that the number of men who die once diagnosed is lowered by more than 50 percent among men eating lots of fish."

While fish is known to have many health benefits, including cutting the risk of heart disease and stroke, the question of whether it could protect against prostate cancer has been "a bit controversial," Szymanski said.

To investigate further, he and his colleagues analyzed 31 studies including hundreds of thousands of patients, reporting their findings in the American Journal of Clinical Nutrition.

Seventeen of the studies were case-control, meaning they compared eating patterns among people with prostate cancer ("cases") and matched controls without the disease. The remaining 14 studies were cohort studies, which followed men over time and compared diets of those who developed prostate cancer to the diets of the men who remained free from the disease.

Overall, Szymanski and his team found no link between eating lots of fish and men's risk of developing prostate cancer. But they did find that men who ate more fish were 44 percent less likely to develop metastatic prostate cancer, meaning disease that had spread beyond the prostate gland. Higher fish consumption also was associated with a 63 percent lower risk of dying from prostate cancer.

Given that the studies included in their analysis used a number of different measurements of fish intake, the researcher said, it's impossible to say how much fish one would need to eat in order to get a protective effect. "All we can say is eating more fish can have some benefit. How many servings of fish or how many grams needed a day, unfortunately we cannot say."

It's possible, he added, that fish may reduce prostate cancer mortality by reducing men's likelihood of developing metastatic disease. The anti-inflammatory effect of fish oils could help fight cancer progression, he and his colleagues suggest in their report.

Several previous studies have indicated that the omega-3 fatty acids in oily fish and fish oil supplements may slow cancer progression by reducing inflammation and by a variety of other mechanisms. The current study did not include fish oil supplements in its analysis.

Because the analysis only describes whether the subjects ate fish and how much, this study cannot determine for sure whether some other aspect of the heavy fish eaters' lifestyles may account for some of the benefits observed.

Fish has known health benefits anyway, and the findings suggest that encouraging men to choose fish more often could have a major impact on public health, Szymanski said.

"Prostate cancer is a very common disease," he added. "If we can possibly introduce a relatively cheap and easy-to-implement policy that could have even a small impact on how this disease affects men, we could make a very big impact overall."