I've experienced higher-than-usual levels of anxiety recently. Today it occurred to me that I've been taking Emergen-C daily for the last couple weeks (about the duration of the elevated anxiety).
I found this blog post, which says (emphases my own)
It is well known that deficiencies or excess amounts of certain vitamins and minerals can cause symptoms of anxiety and panic attacks. Most vitamins and minerals are harmless and if you get more than you need, the extra just gets excreted, mainly via urine.
However, there are some minerals such as copper, manganese and selenium that are stimulatory in excess and can cause neurological symptoms (again levels are different for each person).
Vitamins B-complex are also stimulating and may cause anxiety and even panic attacks in some people taking higher doses. Particularly people who have gene mutations of the MTHFR genes need to seek advice on which form of B vitamins (activated or otherwise) are suitable for them, as they can experience side effects.
However, I can't really find supporting information on this. I have found multiple articles that state B12 intake can reduce anxiety if you are deficient.
I have also found multiple instances of other people correlating increased anxiety with multivitamin intake, but in every instance (other than the article quoted above) the consensus seems to be that it is not caused by the multivitamin.
So I guess my question is, are there any studies or documented cases of a multivitamin causing increased anxiety? It seems too many people have made this correlation (myself included) for it to be a coincidence. Maybe not?