SLEEP
A large number of studies have demonstrated that caffeine increases the time needed to go to sleep (1) and reduces (2) the duration of sleep. However, there are large individual differences in the effects of caffeine on sleep. For example, in one study caffeine given in the early morning had effects on the subsequent nights sleep (3) whereas in a second study consumption of caffeine at bedtime had no adverse effects on sleep the same night (4). One explanation for these individual differences is that habitual consumers of caffeine are less likely to report sleep disturbances than infrequent consumers of caffeine (5). Another explanation may be that tolerance to the effects of caffeine on sleep develops in habitual consumers (1) and there are no withdrawal effects when caffeine consumption is discontinued (6). Even when caffeine consumption produces sleep disturbances this may not be translated into changes in mood and performance the following day (7).
There is little evidence for associations between caffeine consumption and sleep. A survey of 760 nurses showed that age and family factors were more important determinants of sleep than caffeine consumption (8). A second study could find no association between caffeine consumption and sleep in 72 shift workers (9). A study of sleep in elderly women could find no differences in levels of caffeine consumption between good and poor sleepers (10).
A 2002 review came to three conclusions about effects of caffeine on sleep “First, large amounts of caffeine (e.g. over 3 mg/kg body weight in a single beverage) consumed in the late evening will prevent individuals from going to sleep and reduce sleep duration. Effects of smaller doses show large individual variation, with high consumers being more resistant to effects of caffeine on sleep. Secondly, the impact of caffeine-induced changes in sleep on behaviour the next day and long-term health is not known. Finally, high levels of caffeine consumption do not appear to be strongly related to sleep parameters.”
This is an area in which there has been very little research so a review published in 2009 (11) is a welcome addition to the available science. The aim of the review was to assess the effects of caffeine abstinence on the quality of sleep. Insomnia is a common problem and abstinence from caffeine is one of the most popular components in sleep hygiene advice. However, to date there have been inconsistent results relating to the effectiveness of caffeine abstinence in improving sleep. The authors of this review conclude that caffeine abstinence for a whole day can improve the quality of sleep and thus recommend that health practitioners include caffeine abstinence as an instruction in sleep hygiene advice for insomniacs.
References:
1. Zwyghuizen-Doorenbos, A. et al. Psychopharmacology, 100, 36-39, 1990.
2. Hicks, R.A. et al. Bulletin of the Psychonomic Society, 21, 24-25, 1983
3. Landolt, H.P. et al. Brain Research, 675, 67-74, 1995.
4. Levy, M. and Zylber-Katz, E. Clinical Pharmacology and Therapeutics, 33, 770-775, 1983.
5. Snyder, S.H. and Sklar, P. Journal of Psychiatric Research, 18, 91-106, 1984.
6. Searle, G.F. Journal of Intellectual Disability Research, 38, 383-391, 1994.
7. Smith, A.P. et al. Journal of Psychopharmacology, 7, 203-206, 1993.
8. Lee, K.A. Sleep, 15, 493-498, 1992.
9. Greenwood, K.M. et al. Work and Stress, 9, 262-271, 1995.
10. Bliwise, N.G. Psychology and Aging, 7, 83-88, 1992.
11. C W M Sin et al, Journal of Clinical Nursing, 18, 13-21, 2009