For joints, you want to be consuming high quality fish oil along with regular consumption of collagen-based foods such as broths and stocks.
With regard to finding a high quality fish oil, I don't find the type of fish is of too much importance, and I have not seen good research on krill oil's superiority over fish oil.
I actually just wrote a 3-step buying guide for fish oil, which was published on my site and over at PrimalDocs if you'd like a more in-depth treatment of what constitutes "high quality". But briefly speaking, as long as the final product is fresh, free of toxins, in the triglyceride form, and you can get at least 1,000mg of both EPA and DHA. My article discusses exactly how to find out if it meets those criteria.
I would just eat canned fish. Wild salmon is probably the best.
Fish oil is pretty shady. I wouldn't be surprised if the majority of brands sell rancid product.
I have been using krill oil. Not sure if it's any better, but i don't get fish burps anymore which may suggest that my body is adequately digesting the contents.
Treatment of sore joints isn't on the list of known things that the active ingredients of fish oil improves. Its popularity is mostly due to development, maintenance and improvement of the nervous system (neuron sheaths love fat). So I wouldn't go overboard if your only objective is joint pain.
If most joint pain is due to inflammation (and some due to pathogens or structural injury), then an anti-inflammatory diet would be a starting point. As to how long the body takes to repair inflammation? A lot longer than drugs that mask the problem with analgesics would be my guess.
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