I do agree that the supplement industry is fraught with fraud; however; my husband was having migraine headaches & vertigo spells...so bad that the family doctor sent him to a shrink.
(whose specialty is migraines) After it seemed like endless imaging tests & various prescribed drugs with no progress, the shrink announced that he had a magnesium deficiency & so, 'prescribed' a pretty large daily dose of OTC magnesium supplement that is available at Costco rather inexpensively.
....knock on wood...it's been a little over a year now since my husband had one of those spells.

So, we're wondering why in the hell the "expert" didn't try this before all of the BigPharma drugs that have three pages of side effects in the first place .
Don't tell me - - - more $$ in more pockets.

And so, this experience has somewhat boosted my opinion of "do-nothing" vitamin-mineral supplements.