Chapter 10Children’s health

Chapter overview

• Introduction

• Physical activity and physical fitness

• Obesity

• Type 2 diabetes

• CVD

• Bone health

• Summary

Introduction

• The majority of studies are observational.

• Differences in maturation may confound findings of studies where only chronological age is assessed.

• Outcome measures are invariably risk factors rather than disease endpoints.

• Childhood is considered to be the period before puberty.

• Adolescence is considered to be the period from the beginning of puberty until adulthood.

Physical activity in young people

• Active transport to school has declined.

• Sedentary behaviour is common and established at an early age.

• Few meet the guideline of at least 60 minutes of moderate-intensity activity daily.

• Activity levels typically decline from childhood to adolescence.

• There are problems making satisfactory measurements.

Moderate-to-vigorous activity levels in boys and girls followed for six

years

Physical activity levels in girls followed from 9 or 10 years of age to

18 or 19 years of age

Physical activity levels in children attending three different primary schools

Children in schools with low amounts of timetabled physical education compensate by being more active outside school.

Note: School 1 – nine hours timetabled PE/wk; school 2 – 2.2 hours timetabled PE/wk; school 3 – 1.8 hours timetabled PE/wk.

BMI values in children and adolescents that predict overweight or obesity in adulthood

BMI 25 kg m2 BMI 30 kg m2

Age (years) Males Females Males Females

11 20.6 20.7 25.1 25.4

12 21.2 21.7 26.0 26.7

13 21.9 22.6 26.8 27.8

14 22.6 23.3 27.6 28.6

15 23.3 23.9 28.3 29.1

16 23.9 24.4 28.9 29.4

17 24.5 24.7 29.4 29.7

18 25.0 25.0 30.0 30.0

Use of percentiles of BMI to indicate overweight (85th) or obesity (95th)

Note: Percentage of US children and adolescents above BMI cut-off points based on reference population, 2008.

Obesity in childhood and adolescence increases the risk for obesity in adulthood

Note: Retrospective study of 854 children born in Washington State.

• Some cross-sectional studies have found an inverse relationship between activity levels and markers for adiposity;

but• this is not a universal finding;

• prospective studies have sometimes, not always, found that higher levels of activity were related to smaller increases in BMI and adiposity.

Does inactivity influence childhood adiposity?

Mean difference in BMI and adiposity in adolescents classified as either inactive or active

Note: Girls were studied longitudinally from age 9 or 10 to age 18 or 19.

‘The evidence base on childhood obesity prevention has increased markedly in recent years … [it] remains extremely limited, and no successful, high-quality, generalizable interventions presently exist.’

(Reilly 2006)

Interventions to prevent childhood obesity

Exercise does not consistently decrease body weight or BMI but 155 to 180 mins/wk of moderate-to-high intensity aerobic exercise is effective for reducing body fat in overweight children and adolescents.

Exercise in the management of over-fatness in children and adolescents

Hospital admissions to English hospitals in children aged 0–18

Physical activity and prevention of type 2 diabetes

• There have been no trials – and there will not be, numbers would be prohibitive;

but

• high levels of activity or fitness have been positively associated with insulin sensitivity and inversely associated with insulin resistance in major studies in the US and Sweden.

Odds of having CVD risk factors in US adolescents aged 12–19 with low

(versus moderate or high) fitness

Prevalence of selected CVD risk factors at age 26 according to TV viewing

between ages 5 and 15

Note: Data from New Zealand, 2004.

BMI and CVD risk markers in obese children and controls (obese and normal weight) at baseline, after one year of intervention and one year after

the end of intervention

Note: Intervention = exercise, nutrition education, behaviour therapy.

Side-to-side differences in BMC of humerus, according to biological age of starting training in tennis/squash players

Bone mineral density in soccer players at weight-bearing and non-weight-

bearing sites

Exercise recommendations for enhancing bone mineral accrual in children and adolescents

Mode Impact activities, such as gymnastics, plyometrics, and jumping, and moderate-intensity resistance training; participation in sports that involve running and jumping (soccer, basketball) is likely to be of benefit, but scientific evidence is lacking.

Intensity High, in terms of bone-loading forces; for safety reasons, resistance training should be < 60% of one-repetition maximum.

Frequency At least 3 days per week.

Duration 10–20 min (two times per day or more may be more effective).

Summary I

• Many young people exhibit low levels of physical activity. Levels typically decline during the transition from childhood to adolescence.

• Physical activity and physical fitness are related in young people, although correlations are often low.

• Activity levels can be increased through school-based programmes which involve the family and/or community.

• The prevalence of obesity among children and adolescents has increased in many countries in recent years.

• Physical activity and adiposity may be inversely related in young people.

Summary II

• Physical activity can contribute to the prevention and management of obesity in children and adolescents, but evidence to support effective interventions is limited.

• The prevalence of type 2 diabetes has increased in children and adolescents in recent years, but remains low in children.

• High levels of physical activity are positively associated with insulin sensitivity and negatively associated with insulin resistance in children and adolescents.

Summary III

• High levels of physical activity and physical fitness are related to healthy CVD risk factor profiles. Exercise training may lead to favourable changes in CVD risk factors in children who exhibit unhealthy profiles.

• Physical activity, particularly high impact activity, promotes bone growth and strength in children and adolescents, but is unlikely to reduce the risk of fracture in old age unless physical activity is maintained.