I think the big picture is huge and not entirely known. One angle: A cause of ADHD is a bad gut biome. This may also affect the bioavailability of micronutrients, thus leading the deficiencies. Compensating for that by taking more, with supplements, could help with additional symptoms.

Long before I had a diagnosis or meds, I had some good runs, few years even, and even back then, I saw the link to certain foods. When fixing multiple problems at the same time, the effect was enormous.

Some caffeine, but well distributed, as a poor man’s stimulant, combined with drinking a lot, very specific foods … I think it was a mix of “medication”, hydration, gut biome (low sugar, probiotic foods) and fixing multiple deficiencies at the same time. When that extra energy results in more physical activity, additional amplification happens.

So yes, I believe that multi-vector attacks on your health problems work in synergy, better than the sum of their parts.

As for iron specifically, a lot can be done wrong. What I recall: Best in the morning before first coffee / tee and some time in-between, with Vitamin C. Personally, I can’t stomach it, so I got to ignore that rule and just take it with the biggest meal.