Is it true that excessive amounts of stress can lead to premature graying of the hair?

Premature Gray: Seeing photos of our presidents before and after their terms in office, you'd have to wonder about stress graying their hair. Still, science so far hasn't documented a direct relationship between stress and hair graying. Graying is usually genetically determined, along with multiple biochemical changes. Hair may be more likely to fall out with stress -- perhaps leaving more gray ones behind.

Yes: Graying of hair is related to genetic predisposition. Age of initial graying is largely a matter of genetics. However stressors: nutritional deficiencies, chemotherapy, traumatic head injuries, low vitamin B levels, zinc deficiency, severe illness, surgery & marked emotional stress may impact earlier depigmentation in people who are already predisposed to gray hair. Aging is a significant factor.