According to a leading hair loss clinic in Britain, The Belgravia Centre, a lack of sleep has been shown to affect the body's immune function, hormone secretion, and physical and mental stamina. "Hair is very sensitive to changes within the body, and hair loss is nearly always the consequence of an internal disturbance," they state on their web site.
How Lack Of Sleep Leads To Hair Loss--And Worse
How Lack Of Sleep Damages Your Hair