Twenty-one-hour melatonin plasma profiles were studied in 15 normal elderly volunteers from the community, and eight who had been in hospital for more than six weeks and who had not been exposed to strong natural lighting. The hospital group had significantly higher daytime plasma melatonin levels, an earlier nocturnal rise, and the timing of their secretory profiles was more variable.These results suggest that currently used artificial and supplementary natural lighting may not be sufficient to suppress melatonin secretion adequately during daylight hours nor act efficiently to entrain day/night secretion of melatonin in a physiological circadian manner. Raised melatonin levels by day and variable secretory profiles at night may account for certain mood and sleep disorders observed in institutionalized people.
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