Go to the doctor, get your yearly blood panel, and then ask them about what supplements you should take. If you have even a mildly varied diet, with occasional vegetables, you shouldn't need much in terms of supplements. The supplement industry doesn't like that answer though because they can sell turmeric at $20 a bottle as a supplement instead of the $4 a bottle it is in the spices section.

Remember that there is NO regulation on supplements, and there's no requirement they even contain the vitamin they claim.