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We aimed to obtain reliable reference charts for sleep duration, estimate the prevalence of sleep complaints across the lifespan and identify risk indicators of poor sleep. Studies were identified through systematic literature search in Embase, Medline and Web of Science (9 August 2019) and through personal contacts. Eligible studies had to be published between 2000 and 2017 with data on sleep assessed with questionnaires including ≥100 participants from the general population. We assembled individual participant data from 200,358 people (aged 1-100 years, 55% female) from 36 studies from the Netherlands, 471,759 people (40-69 years, 55.5% female) from the United Kingdom and 409,617 people (≥18 years, 55.8% female) from the United States. One in four people slept less than age-specific recommendations, but only 5.8% slept outside of the 'acceptable' sleep duration. Among teenagers, 51.5% reported total sleep times (TST) of less than the recommended 8-10 h and 18% report daytime sleepiness. In adults (≥18 years), poor sleep quality (13.3%) and insomnia symptoms (9.6-19.4%) were more prevalent than short sleep duration (6.5% with TST < 6 h). Insomnia symptoms were most frequent in people spending ≥9 h in bed, whereas poor sleep quality was more frequent in those spending <6 h in bed. TST was similar across countries, but insomnia symptoms were 1.5-2.9 times higher in the United States. Women (≥41 years) reported sleeping shorter times or slightly less efficiently than men, whereas with actigraphy they were estimated to sleep longer and more efficiently than man. This study provides age- and sex-specific population reference charts for sleep duration and efficiency which can help guide personalized advice on sleep length and preventive practices.

Data from two screening projects on cardiovascular risk factors were used to analyze the trend in serum total cholesterol level in the Netherlands between 1974 and 1986. Cholesterol levels were measured in a single reference laboratory of the World Health Organization throughout the entire study period. Between 1974 and 1980, about 30,000 men and women aged 37 to 43 years (mean age, approximately 40 years) were screened. A decrease in mean serum total cholesterol level was observed until the end of 1977, when it was followed by an increase. This resulted in a net change over the entire study period of -0.07 mmol/liter (3 mg/dl) in men and -0.03 mmol/liter (1 mg/dl) in women. Between 1981 and 1986, about 80,000 men aged 33 to 37 years (mean age, 35 years) were screened. During this period, a decrease of 0.20 mmol/liter (8 mg/dl) in the mean total cholesterol level was observed. In spite of the decline in the mean total cholesterol level, the prevalence of cholesterol values of greater than or equal to 6.5 mmol/liter (greater than or equal to 251 mg/dl) in young adult men was still high in 1986 (16 percent). A further reduction is therefore desirable. The decline in the mean total cholesterol level in young adults might indicate that a further decline in mortality from coronary heart disease can be expected.