Increasing omega3 was a major one for me, definitely decreased chronic inflammation. The problem occurs if one's omega6:omega3 ratio is off, and most westerner's diets are very high in predominantly omega6 fatty acids[0] (such as olive oil, and most other oils). Though if you choose to supplement omega3, make sure it is controlled for mercury-contaminants.

With fat-soluble vitamins such as Vitamin D, be vary of vitamin toxicity (Hypervitaminosis[1]), as they accumulate in the body. But you'd probably have to take a huge amount over a long time to get there.

Another interesting supplement might be L-Carnitine[2], especially if you eat little/no meat.

[0] https://pubmed.ncbi.nlm.nih.gov/12442909/

[1] https://en.wikipedia.org/wiki/Hypervitaminosis

[2] https://examine.com/supplements/l-carnitine/#effect-matrix

How did you figure out the change decreased chronic inflammation? Was there a change in inflammatory markers or something? Or more of a hunch?

I'm a bit shy to admit, but the most objective marker was a significant reduction in acne (on my shoulders). But overall I also feel a lot calmer, I digest food better, I sleep better, and some other things that are hard to pinpoint. I just have an overall greater feeling of well-being. I know this is only n=1 and hard to prove that it's due to omega3, but I just really feel like it is closely related.

I also have to point out that I've eaten a vegetarian diet since about 2008. I always thought I had a pretty healthy diet and blood work confirmed that, but it appears that it didn't control for omega3 concentrations. Part of that diet was that I consumed large amounts of (in particular) olive oil (omega6), and almost negligible amounts of omega3.

If you're feeling that much better overall, it's probably much healthier for you regardless of why that happens to be. Sounds like a good deal. :)