I take vitD everyday Nov-March and C, for a few days after I've been around anyone who is sick. I think it helps. I made it almost 3 years without a cold or stomach bug.
Past that, though, the body only absorbs a fraction of what is in supplements compared to getting it from food. If the diet is lacking nutritious foods, it probably helps. With a good diet, it's probably pointless but not harmful. Like with the C, I think I'd be better off if I ate C rich foods for a stretch instead, but I'm not real fond of potatoes or oranges😅 that's my thoughts anyway.