Altered Diurnal Serum Melatonin Rhythm in Blind Men

Visual Impairment and Circadian Rhythm Sleep Disorders

“…The first report of melatonin rhythms In the blind was made by Smith and colleagues who showed that four blind men had higher day - than night-time melatonin levels, 44 the opposite of what would be expected in sighted subjects (Figure 1) . Subsequently, Lewy and Newsome 45 Investigated plasma melatonin profiles In 10 blind subjects (9 NPL, 1 LP) and showed that six subjects had an abnormally timed melatonin rhythm, three of these being phase-advanced and three being phase-delayed.…”

Melatonin and Human Chronobiology

“…Accordingly, we proposed that blind people can be categorized into three types: Those who are entrained at the normal phase, those who are entrained at an abnormal phase, and those who are free-running. Smith et al (1981) reported that serum melatonin values in four blind people were greater at 1400 (86-142 pg/ml) than at 2300 (64-72 pg/ml). However, these data should be interpreted with care, because high daytime levels were routinely found with the nonspecific RIAs in use at the time (Smith et al 1977).…”

Melatonin in Circadian Sleep Disorders in the Blind

“…Environmental light acting via retinal photoreceptors and the retinohypothalamic tract entrains suprachiasmatic nuclei activity to 24 h. Blind people, in particular those with no light perception (NPL), may lack entrainment by light and exhibit disturbed circadian rhythms (melatonin, cortisol, sleep-wake cycle, core body temperature). Studies of blind subjects have confirmed the presence of disrupted rhythms of melatonin [1][2][3][4][5][6][7][8][9], cortisol [4,[10][11][12][13][14][15][16], core body temperature [4,6,9,17] and the sleepwake cycle [4,7,[18][19][20][21][22].…”