A 16-year study, which dove into the data of almost half a million men and women, concludes that a diet rich in fish predicts a longer life.

Consuming fish has long been recommended as part of a nutritious diet. Rich in high-quality proteins, vitamins, and healthful oils, fish is roundly considered a healthful choice.

Oily fish are rich in omega-3, and, over recent years, this oil has received a great deal of attention from medical researchers and supplement manufacturers alike.

Evidence is far from overwhelming, but scientists have already searched for any associations it might have with lower cancer risk, improved cardiovascular health, and reduced inflammation.

Other studies have tried to find links between omega-3 and mental health, aging, and vision. Work is ongoing, but because findings are often contradictory or weak, the relationship between a fish-heavy diet, omega-3 intake, and good health are still up for debate.

Fishing for details

Recently, a team of researchers set out to gain more clarity on the important question, "Does eating fish impact mortality risk, and how does omega-3 fit in?"

The scientists delved into data from the NIH-AARP Diet and Health Study, which is the largest study on health and diet ever carried out. In all, they followed 240,729 men and 180,580 women for 16 years.

Participants provided information about their dietary habits, and their health was monitored. Over the course of the study, 54,230 men and 30,882 women died. The results have been published recently in the Journal of Internal Medicine.

The main finding is that consuming more fish and long-chain omega-3s reduces total mortality.

And, looking further into these data, the researchers found that men who ate the most fish had a 9% lower mortality risk than those who ate the least.

When the researchers drilled down into specific causes of death, they found that males who ate the most fish, compared with those who ate the least fish, had a:

• 10% reduction in cardiovascular disease mortality
• 6% reduction in cancer mortality
• 20% reduction in respiratory disease mortality
• 37% reduction in chronic liver disease mortality

Comparing the highest and lowest fish consumers among female participants, they measured an 8% reduction in overall mortality and a:

• 10% reduction in cardiovascular disease mortality
• 38% reduction in Alzheimer's disease mortality

The scientists switched their analysis to look specifically at the level of omega-3 intake calculated from the participants' food intake surveys. They discovered that men and women who consumed the most omega-3 had 15% and 18% reductions in cardiovascular mortality, respectively.

The results are intriguing and add to the evidence for the health benefits of omega-3 and fish in general. However, not all fish was protective.

Avoid the frier

Importantly, these results did not apply to fried fish. Among men, the consumption of fried fish had no impact on mortality risk. Among women, however, higher consumption of fried fish increased the risk of cardiovascular mortality, respiratory disease mortality, and overall mortality.

This is probably for a number of reasons. For instance, frying the fish creates trans-fatty acids and also increases the energy density of the end product, both of which could potentially undo any good work that omega-3s carry out.

Overall, the authors conclude:

"Consumption of fish and [omega-3s] was robustly associated with lower mortality from major causes. Our findings support current guidelines for fish consumption while advice on non-frying preparation methods is needed."

The study does have some shortfalls, though. For example, it was observational, so it is difficult to tease apart cause and effect. Also, the participants—on average—did not consume a great deal of fish when compared with those in other studies.

However, the project was large—it is the largest study to investigate dietary fish and mortality to date—and the long follow-up duration was key; similarly, there were a relatively high number of deaths, making the analysis more robust.

For these reasons, the results provide a welcome boost to the evidence in favor of the protective power of fish-based foods.