I've googled the subject, but nothing really stood out: 

I've been vegan for about 8 or 9 years and I've noticed that the hair on the crown of my head is very thin. When I was a omnivourous teen I remember that my hair was on the thin side, but not quite like today. When I hold my bangs up it's a bit too easy to see my scalp. Needless to say, for a female, this is quite perplexing.

  Some observations: