I took Omega-3 supplements for years. Then my doctor told me that it was bad for me. She also told me that Vitamin E supplements are bad for us, and cause prostate cancer in men.
Because I'm "that guy," I didn't accept her word for it. I started researching. I did find that the Omega-3 studies didn't show much support for taking it. I also found that the information she had about Vitamin E was only partially correct. There are several types of Vitamin E. Most of the supplements contain only D-Alpha Tocopherol. By itself, D-Alpha Tocopherol apparently may contribute to prostate cancer. But supplements that contain multiple types of Tocopherol don't contribute to prostate cancer. So, rather than stop taking Vitamin E supplements, I switched from the one I had been taking (which was a D-Alpha type) to a "mixed Tocopherol" type.
The Vitamin E studies were somehow related to the fish oil studies, but it's been a few years so I don't remember which one I was researching that led me to the other.