I've been working out consistently for the past 7 years so it's hard for me to say if it's had an effect. What I HAVE noticed is that when I do more CARDIO (in non competition season I do very little, MAYBE twice a week) and eat more veggies/salads, my hairs to grow much faster.
I'll be able to update my response to this in about a month or so as I'm making a transition from doing bodybuilding to doing figure competitions. I have to lose a bunch o'weight and stay leaner (and less muscular) in the off season. I'm currently doing cardio, 20-30 minutes a day, 6 days a week.