Is caffeine a factor in subjective insomnia of elderly people?

Subjective insomnia is more prevalent in elderly than in young populations. In order to examine the relationship between caffeine and sleep quality we studied 181 community-dwelling subjects over a wide age range and 53 elderly patients receiving continuing hospital care. Subjects completed a sleep questionnaire and data concerning smoking, alcohol, use of hypnotics and caffeine-containing substances were recorded. Late afternoon plasma caffeine concentrations were measured in a sub-group of 87 of the community-dwelling subjects and in the hospitalized patients. For the group as a whole, there was a significant negative correlation between age and coffee but not tea consumption (p < 0.001). A global score of sleep quality was significantly inversely related to age (p < 0.001). For the community-dwelling population, the median plasma caffeine concentration was 1.71 micrograms/ml (range 0.10-6.74) and showed a significant correlation with sleep quality (p < 0.05). In contrast, for the hospital dwelling population, median caffeine concentration was higher in patients reporting sleep problems than in those without (p < 0.05). Self-reported consumption of coffee and tea did not correlate with plasma caffeine concentrations. It is possible that people with poor sleep quality, residing in the community, are aware of the stimulatory effects of caffeine and lower their intake accordingly, whereas hospitalized elderly patients, who have less control over their environment, do not.