Earlier quoted context omitted.
I get your joke but the concern he expresses is only relevant to the Omega-3. In the case of vitamin D, outside of sunlight exposure, supplements are basically your only practical option. Furthermore, the foods mentioned often have it added (milk nearly always does) and so one would want to be aware of that before adding it further from another supplement. At worst, the paragraph is just a poorly constructed catch al…
Here are my concerns with their statement: First, I recall warnings about too much fish consumption due to mercury levels in the fish. So how much fish consumption is necessary to get the required omega 3 and does the benefits balance out over the harm caused by the mercury? And are there any particular kinds of fish to consume to limit mercury exposure while getting the benefits of omega 3? Second, as far as I know…
Mercury bioaccumulates in the ecosystem. That means higher levels in fish that eat fish, and highest levels in fish that eat fish that eat fish. It also accumulates over a lifetime, so longer lived fish have higher levels.
Farmed fish (in this US mostly tilapia and salmon) have other issues, but mercury isn't a generally concern. For wild fish, the small ones--anchovies, herring, sardines--are low in mercury, along with catfish, pollock, shad, and haddock.
The worst for mercury that are widely eaten are tuna (sushi or steak grade, the species they used for canned tuna aren't as bad), certain types of mackerel, and grouper.