I think it is important to have regular blood-tests done in order to pin-point exactly what vitamins/minerals you need to get more of. If not, you could end up taking supplements that your body does not really need. Since supplements are expensive, that would be a huge waste of money. The cost of having blood-tests probably would equal the amount that one migth be spending on supplements one does not really need. I find that it is a lot of hype out there about what supplements to take for this and for that, and it can get really confusing! After I had blood-tests done, it was discovered that I was very low on vit B12, as iron as well. My doctor advised me to take iron-supplements (and what dose), and I also got weekly injections of vitB12. It helped me a lot in terms of lessening symtoms of long and debilitating periodes of depression (which is my major BP-symptom).
I also think it is important to eat a diet that contains high amounts of the vitamins I typically am low on. I searched the internet to find out, and came up with a long list of foods high in vit B12, iron and vit D. I chose to eat more of those, after having determined which ones I liked. And I am a firm believer in taking vit D-supplements. I hope this was helpful! It`s a jungle out there of good and less good advice about these things!