The vitamin D in a general multivitamin is a maintenance amount, nowhere near what is used to correct a real deficiency. If your level is genuinely low, that is a prescribing conversation with blood tests behind it, not a shelf in the chemist.

You cannot patent a plant, so there is little commercial reason to fund expensive trials of one. When you read that a herb has no evidence, that often means nobody paid to look rather than that somebody looked and found nothing.

If you are testing whether a food affects you or your child, the test has to be complete. Among children with suspected sensitivity to artificial colouring, most reacted to as little as 100 mg, so a bit left in is enough to blur the answer.

Even where a herb has good evidence behind it, that evidence belongs to the plant and not to the bottle in your hand. Testing keeps turning up products that do not contain what the label says.