The whole vitamin B-complex is important for healthy hair. The B-complex includes B1, B2, B3, B6, B12, biotin, choline, folic acid, inositol, and para-aminobenzoic acid. It's best to get these vitamins from real foods because in this way they are more bioavailable - easily digested and better assimilated. Also there may be unidentified members of the B-complex that have not yet been synthesized and put into pills. These vitamins work synergistically - the total effect is greater than the sum of the individual vitamins.
Another important factor is that taking too much of one member of the complex can throw out of balance the other members. I'm not an advocate of megadoses of any vitamin or mineral. If you get your nutrients from real food you never have to be concerned about overdosing. Of course many people who start reading about the power of vitamins get their information from the merchants who sell supplements, usually at inflated prices. And often they think that if two tablets of inositol or biotin are good for the hair, five or six tablets will be even better. I know the thinking because I thought the same way back in the stone age.
Two real foods that are rich in the B-complex are brewer's yeast powder and plain yogurt with active and live cultures. I've written a lot about the nutritional value of brewer's yeast but I recently learned about the value of a certain kind of yogurt thanks to this post on my other website about facial exercise - http://www.shapeyourface.com/syfbb/viewtopic.php?f=9&t=85
I read The Probiotics Revolution
by Gary Huffnable that Horsegirl mentions. These yogurts with live and active cultures are great sources of all the B vitamins along with many other vitamins and minerals. Don't get the yogurt with just active cultures though. Get it with live
and active cultures. Read through the thread that I gave the link to - interesting stuff.