Researchers have recently discovered that benefits of tuna contains the mineral selenium in an unusual form called selenonein. This form of selenium plays an important role in fish health by serving as an antioxidant and protecting fish’s red blood cells from damage by free radicals. Interestingly, it can also bind with mercury compounds in the fish’s body (including methylmercury or MeHg) and reduce the risk of mercury related problems. Because there are approximately 20-30 micrograms of selenoneine in a 4-ounce serving of tuna, we are likely to get some of this same antioxidant protection when we eat tuna. Equally interesting, tuna may turn out to be a fish that, even when contaminated with mercury, could present a lower risk of mercury than might otherwise be expected due to the presence of selenonein. There is some evidence showing that lower concentrations of selenoneine and selenium itself may be present in fresh tuna that lacks its characteristic reddish color and is more watery and softer in texture at the time of purchase. However, more research is needed to determine exactly how the selenium content of tuna relates to both its appearance and its potential mercury risk.
A single category of nutrients has not been more clearly determined to have anti-inflammatory health benefits than omega-3 fatty acids, and tuna is equally well established as an important food source of omega-3s. In an average 5-ounce can of tuna, you’re likely to get about 7-28 milligrams of EPA (eicosapentaenoic acid) and 140-850 milligrams of DHA (docosahexaenoic acid). Both EPA and DHA are critical omega-3 fatty acids for proper regulation of the body’s inflammatory system and prevention of excessive inflammation. Generally speaking, you are likely to get more omega-3s from canned albacore than canned “light” tuna made from other species of tuna like skipjack (but also sometimes including yellowfin, tongue or bigeye). But you are also likely to get more mercury from canned albacore because albacore is generally larger and older, as it has had more opportunities to accumulate mercury from polluted ocean waters.