This is a great comment, and hits the nail on the head.

I've spent much of the past 10 years trying to understand and overcome a somewhat mysterious fatigue illness that seems most likely to be a general autoimmune condition.

One of the approaches I've tried along the way is to consume large amounts of various supplements, including vitamins, minerals, amino acids and herbs (basically, whatever was the latest thing I heard some convincing-sounding "expert" recommend).

What I ended up realising was that any high-dose supplement intake might initially make me feel better, but after a while it would actually make me feel worse.

As I understand it now, having devoted a lot of time to researching and experimenting with this, is that a deficiency in any nutrient is less to do with a lack of it in the diet and more to do with the body's ability/willingness to absorb and utilise it [1].

And so the more of any given nutrient that you try and shove into the body, the more you actually throw it out of balance, as it now has to deal with an excess of something it was already struggling with or resisting, as well the increased presence of that nutrient relative to other important nutrients.

More recently I've had much better success at improving my condition by learning how to match my nutrient intake to what my body actually needs and can handle at any given time (via diet and very sparing, selective supplement intake), and that seems to now have me on a steady path to full recovery.

[1] Sure there are many people in the world who are ill due to inadequate intake of certain nutrients from their diet, but that's more of an issue in poverty-stricken societies, as opposed to developed-world societies where most people have access to healthy-enough diets yet many still suffer from chronic illness.