INFORMACIÓN REQUERIDA EN EL PROSPECTO A) Portada del prospecto

1.9.1. Sedentary behaviour

Despite inconsistencies between some domains of SB and health outcomes in children and adolescents, the hazards of excessive sedentary time are more clear and consistent in adults (104,106). Preventive measures of SB during early stages of the life course are important for two reasons. Firstly, there is consistent evidence that SB during childhood tracks (defined as “a tendency of individuals to maintain their rank or position in a group over time” (137)) into adolescents and then adulthood. Secondly, daily time spent sedentary increases continuously during this transition.

Several reviews have examined SB tracking. A recent review (138) of 19 individual samples of children observed tracking of both screen time and overall sedentary time in the range of r = 0.3-0.5 (moderate-strong) during the primary-middle-high school transition. It was estimated that this equated to a 20-30 min/day increase in total sedentary time per year. A systematic review by Biddle et al (139) explored tracking of SB in young children through to adulthood. In 21 independent samples in prospective studies, follow ups ranged from one to 27 years. Across all age ranges (3-5 years; 6-11 years, 12-18 years) and lengths of follow up, there appeared to be consistent tracking at a predominantly moderate level (r = 0.30-0.49) in TV viewing, computer and video game use and screen time. Total sedentary time demonstrated moderate tracking in 3- 5 year olds after 1, 2 and 3 year follow ups and in adolescents tracking was small into early adulthood in accelerometer and questionnaire data after two years follow up (no studies were included with children aged 6-11 years). Tracking was generally stronger in studies with shorter periods of follow up in all measures of SB, and TV viewing demonstrated the strongest tracking values. The combined evidence was limited to mostly self-report measures, mostly short follow-up periods and being set across just four developed countries (mostly USA, New Zealand, Australia and the UK). Furthermore, the authors stated that almost all studies used correlation coefficients to report tracking, which was the only statistic the review authors reported for comparability purposes, which carries several potential inaccuracies (139). Nevertheless, this review

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demonstrated that different types of SB, even when measured differently, appears to track from childhood into adolescents and through to adulthood in both boys and girls. Total sedentary time, has been seen to track from childhood into adolescents and continually increase in duration during this transitional period in a UK cohort (96). In a longitudinal study with a demographically diverse sample, children wore an accelerometer for 7-days at four measurement periods; 7 years, 9 years, 12 years and 15 years of age (three follow ups). Total stationary time and breaks in stationary time tracked moderately from 7 to 15 years of age. At every follow up period, total stationary time and median stationary bout duration increased and the frequency of breaks in stationary time declined. These trends were consistent across all levels of stationary time. During waking hours the proportion of time spent stationary increased by 22.9% at 15 years old compared to 7 years old, with increases of 4.2%, 9.2% and 8.8% observed between 7 and 9, 9 and 12 and 12 and 15 years of age, respectively. The evidence taken together suggests that excessive sedentary and stationary behaviour, deleterious to health in adulthood, originates in childhood and adolescence (96,139). These trends have also been observed in self-report screen time in a prospective study with UK children (140). Between the school years of 7 and 11 (10-16 years of age), screen time increased every year, with an average increase of 2.5h/week in boys and 2.8h/week in girls (140).

Current UK evidence of sitting and stationary time in adults (office workers) consistently demonstrates that over 10 hr/day is spent sedentary in self-report (141,142), accelerometer (143) and inclinometer determined data (144). As already detailed in section 1.6, adults who spend >8h/day sitting have an increased risk of all-cause mortality of between 10% and 27%, depending on daily levels of PA. While meeting PA recommendations provides some protection from excessive daily sitting, most adults, both male and female, young and old, fail to meet PA recommendations in the UK (145), which is outlined in the next section. Furthermore, as outlined in Figure 1.3, TV viewing would appear to increase continuously from young adulthood to middle ages and beyond in UK adults (145). This all suggests that the progression from childhood into adulthood is accompanied by tracking and a continual increase in sedentary/stationary behaviour, which results in many adults in the UK being highly sedentary/stationary and probably of elevated risk of mortality and morbidity (102,104,106).

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Figure 1.3. self-reported mean TV viewing by sex and age in adults from Health

Survey for England data (2016). Source: Health Survey for England (2016) (145).

1.9.2. Physical activity

As already stated in section 1.1, the evidence for the importance of regular PA on health outcomes during all stages of the life course are compelling (10,146). Unfortunately however, unfavourable trends in PA from childhood into later years are apparent. In a recent review of reviews, longitudinal studies and data from the ICAD, the evidence seems to suggest that a decline in MVPA first occurs around early childhood (i.e. five years of age) in both sexes and not during adolescence as previously thought (97,147). In agreement with Janssen (96), the overall evidence also suggested that an increase in sedentary/stationary time first occurs during this stage. Reductions in PA and increases in sedentary/stationary time occurring around early childhood have also been observed in other recent prospective studies with objective data in UK samples (148,149). For example, accelerometer data (N = 545) from the Gateshead Millennium Cohort study demonstrated a continuous reduction in MVPA every two years from age 7 to 15 years. Between these ages, MVPA reduced by 24mins/day (from 76 mins/day to 51 mins/day) in boys and by 22mins/day (63 mins/day to 41 mins/day) in girls. In 1299

Base: Aged 16 and over

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children from a city in England, Jago et al. (149) observed annual reductions in MVPA of 7 min/day in girls and 3 mins/day in boys as well as an annual increase in stationary time of 84 mins/day in girls and a 74 mins/day increase in boys between year 1 and year 4 of primary school.

The continual decline in PA from early childhood to late adolescents outlined in these studies is a trend that continues through adulthood. Figure 1.4 represents the self- reported proportion of men and women meeting aerobic and muscle strengthening recommendations within the PA guidelines from Health Survey for England data in 2016 (145). The figure clearly demonstrates that in both males and females, there is a continual decline in health-enhancing PA from early adulthood through middle age and older ages.

Figure 1.4. Self-reported proportions of men and women meeting aerobic and muscle

strengthening recommendations within the UK PA guidelines from Health Survey for England data (2016). Source: Health Survey for England (2016) (145)

1.9.3. Obesity

The development of obesity during childhood not only influences impaired health (i.e. hyperinsulinemia, impaired glucose tolerance) at this stage of life (150,151), but also increases the risk of cardio-metabolic health issues in later life (152). Rates of obesity

Men Women 50 40 30 20 10

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(defined by BMI z-scores) have increased in recent decades in children in developed countries (153,154) and currently one in six children internationally is overweight or obese (5). There is longitudinal evidence that BMI increases continuously from childhood into adolescents (129) and national survey data in England (HSE) clearly demonstrates that obesity rates increase from childhood through to adulthood, with BMI and waist circumference generally highest during the later stages of middle age (155). It is important to consider the development of obesity during the life course within the context of SB and PA because some domains of SB and low levels of PA contribute to the development of obesity during childhood (11,42). Furthermore, these relationships may be bi-directional where obesity in children influences more time spent sitting (15) and less PA (156). Figure 1.5, taken from HSE data in 2016 (145), highlights how sedentary time increases as BMI category increases from normal weight to overweight to obese in adults.

Figure 1.5. Self-reported proportions of adults that were sedentary for four hours or

more per day on weekdays by BMI category and sex. Source: Health Survey for England (2016)

Base: Aged 16 and over

Men Women 60 50 40 30 20 10

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1.9.4. The need for lifestyle interventions during childhood

Low levels of PA and some domains of SB are negatively associated with obesity and other health outcomes during childhood (9,10,42). Furthermore, adulthood is when common NCDs typically manifest clinically (157) and when excessive SB/stationary time, low PA and obesity typically have a greater attenuating health effect. With SB/stationary time and obesity rates continually increasing (96,155) and PA decreasing beyond childhood (147), and the initial development of many NCD risk factors occurring during childhood (8), it would seem critical for healthy lifestyle strategies to be implemented during an early stage of life. This includes SB, not only by reducing time spent in more harmful behaviours (TV viewing), but also by reducing total daily sedentary time and breaking prolonged periods of sitting. Interventions during childhood can create positive daily SB profiles before SB patterns become entrenched into adult living habits (41). Furthermore, early modification can limit the number of life years that are spent exposed to potentially harmful sedentary time. The need for this preventative action is reflected in the worldwide development of policy and research interventions to reduce SB in children currently taking place (96).

1.10. UK Sedentary behaviour and physical activity guidelines for