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Too Little Or Too Much Sleep?

Updated May 2008 - A study just published in the journal SLEEP has attempted to quantify the relationship between duration of sleep and obesity for both children and adults using cross-sectional research from around the world. The study shows that children and adults who are short sleepers have a consistent increased risk of obesity.

Francesco P. Cappuccio, MD, of Warwick Medical School and colleagues identified 12 studies on children and 17 studies on adults that included the following criteria: report of duration of sleep as exposure, body mass index (BMI) as continuous outcome and prevalence of obesity as categorical outcome, number of participants, age and gender.

Dr. Cappuccio said that the study showed a consistent pattern of increased likelihood of being a short sleeper for people who are obese, both children and adults.

"By appraising the world literature, we were able to show some heterogeneity amongst studies in the world. However, there is a striking consistent overall association, in that both obese children and adults had a significantly increased risk of being short sleepers compared to normal weight individuals. The size of the association was comparable (1.89-fold increase in children and 1.55-fold increase in adults). This study is important as it confirms that this association is strong and might be of public health relevance. However, it also raises the unanswered question yet of whether this is a cause-effect association. Only prospective longitudinal studies will be able to address the outstanding question," said Dr. Cappuccio.

Sleep and cardiovascular disease

Research from the University of Warwick and University College London published in SLEEP found that both lack of and too much sleep can more than double the risk of death from cardiovascular disease.

Researchers studied the impact of sleep patterns on mortality among 10 308 civil servants included in the "Whitehall II" cohort at two points in their lives (1985-1988 and 1992-1993). Having adjusted for factors such as age, sex, marital status, employment grade, smoking status, physical activity, alcohol consumption, self-rated health, body mass index, blood pressure, cholesterol and other physical illness researchers were able to identify the effect of changes in sleep patterns. They found that those who had cut their sleeping time from the recommended seven hours when first recorded to five hours or less demonstrated by 2004 a 1.7 fold increased risk in mortality from all causes and a two-fold increased risk of death from cardiovascular disease.

Professor Francesco Cappuccio of Warwick Medical School said:

"Fewer hours sleep and greater levels of sleep disturbance have become widespread in industrialized societies. This change, largely the result of sleep curtailment to create more time for leisure and shift-work, has meant that reports of fatigue, tiredness and excessive daytime sleepiness are more common than a few decades ago. Sleep represents the daily process of physiological restitution and recovery, and lack of sleep has far-reaching effects."

The researchers also found that too much sleep was associated with increased mortality with individuals describing an increase in sleep duration to 8 hours or more a night more than twice as likely to die but predominantly from non-cardiovascular causes.

Dr Jane E. Ferrie from University College London Medical School analysed data from 10 308 volunteers between 35 and 55 years of age. Baseline screening (Phase 1) conducted between 1985 and 1988 involved a clinical examination and a self-administered questionnaire. Data collected at Phase 3 (1992-1993) also included a clinical examination (8104 participants) and questionnaire (8642 participants).

Results indicated U-shaped associations between sleep at Phase 1 and Phase 3 and subsequent cardiovascular and non-cardiovascular mortality from all causes. A 110 per cent excess risk was identified in both cases: cardiac mortality associated with a decrease in sleep duration among those sleeping six, seven or eight hours at Phase 1; and non-cardiac mortality with increase in sleep duration among those sleeping seven or eight hours. These associations remained largely the same after adjustment for socio-demographic factors, existing mortality and health-related behaviors.

Francesco Cappuccio explained:

"Short sleep has been shown to be a risk factor for weight gain, hypertension and Type 2 diabetes sometimes leading to mortality but in contrast to the short sleep-mortality association it appears that no potential mechanisms by which long sleep could be associated with increased mortality have yet been investigated. Some candidate causes for this include depression, low socioeconomic status and cancer-related fatigue."

"In terms of prevention, our findings indicate that consistently sleeping around 7 hours per night is optimal for health and a sustained reduction may predispose to ill-health."

Optimum Sleep

The American Academy of Sleep Medicine offers the following advice on how to get an optimal night's sleep:

  • Follow a consistent bedtime routine.
  • Establish a relaxing setting at bedtime.
  • Get a full night's sleep every night.
  • Avoid foods or drinks that contain caffeine, as well as any medicine that has a stimulant, prior to bedtime.
  • Do not go to bed hungry, but don't eat a big meal before bedtime either.
  • Avoid any rigorous exercise within six hours of your bedtime.
  • Make your bedroom quiet, dark and a little bit cool.
  • Get up at the same time every morning.

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