Drinking alcohol before sleep can be viewed as having both a positive and negative influence on sleep. Most research suggests that consumption of alcohol before sleep has a detrimental impact on sleep quality and quantity. Due to alcohols fast metabolism, the effects of alcohol on sleep can change between the first and second half of the night. In the first half of sleep research has shown that there is a decrease in sleep latency, reduction in REM sleep (Rapid Eye Movement) and an increase in non REM sleep. In the second half of the night, sleep can be interrupted with frequent wakings and increased REM sleep and dreaming. Recent research has looked at the effects of alcohol consumption on blood alcohol levels and sleep. The researchers looked at two blood alcohol levels which were 0.03% which was considered normal consumption or 0.1% which was considered abuse of alcohol. The researchers found that when participants blood alcohol levels were 0.1% there was a decrease in sleep latency. When the researchers examined the nights sleep in two halves there were a number of differences between the high and low alcohol dose. In the first half of sleep, the higher alcohol dose resulted in reduced wakings, increase slow wave sleep and decreased REM. However in the second half of sleep, this high dose resulted in increased light sleep. This research supports data which suggests that in the first stage of sleep, high doses of alcohol will give an individual a hypnotic like effect. However in the second half of sleep a high dose of alcohol will lead to sleep disturbance. Alcohol should not be viewed as a suitable hypnotic and it is likely to overall cause impairment in sleep.
Caffeine is a mild central nervous stimulant which can be found in a range of products with coffee and tea being the most common. Most research suggests that caffeine impairs sleep, although it is important to acknowledge that there are individual differences among tolerance levels. In a study looking at the effects of caffeine on sleep, it was found that when caffeine is administered 2 hours before bedtime it can increase the time it takes a person to fall asleep and decrease total sleep time. These effects occur with doses of 100mg or greater. Several researchers have looked at the effect of caffeinated coffee on sleep onset latency, sleep quality and quantity. From research it has been found that when one cup of coffee was taken 30 minutes before sleep this had little effect on sleep. When two cups of coffee were taken this results in small changes in the early night of sleep. However when four cups were taken this showed major impairment in all major measures of sleep.
In a naturalistic investigation of day-long consumption of tea and coffee, Hindmarch et al (2000) provided participants with equal-volume drinks equivalent to either one or two cups of tea (containing 37.5 or 75 mg caffeine) or one or two cups of coffee (containing 75 or 150 mg of caffeine), or water in a randomized cross-over design, four times per day. In this study, there was a dose-dependent relationship between caffeine and sleep onset, sleep time, and sleep quality. There was some indication that the individuals with the lowest habitual intake of caffeine were most influenced by the caffeine intake, evidenced by greater disturbances in sleep.
The negative influence of caffeine on sleep is a big concern for athletes who use high doses to improve performance, especially for events which are held in the evening. Evidence suggests that this is a concern, with athletes reporting that they struggle to fall asleep following caffeine ingestion. We know how important sleep is for recovery and therefore athletes should be aware of how caffeine can affect performance.
Another nutritional factors which can be linked to sleep quality and quanity can be related to hydration. In a recent survey looking at the sleep habits of athletes, a major reason for sleep disturbances was waking up in the middle of the night to urinate. One reason for this is because of the need to rehydrate your body after an evening of training sessions which can result in hyper hydration. Therefore athletes must be aware of the amount of fluid they are drinking in evening training sessions.