Who knows? But people think it helps their health, and they're taking a lot of it. But, turns out it can be really bad for the environment, because the fish most brands use-called menhaden-it is an important cleaner of algae. Now that they use the fish to make the oil capsules, there aren't that many of the fish around to do their other job. Oops. There are ways around this, like flax oil and high-quality fish oil that use sustainably harvested fish. Consider switching.