Growing up in Scotland: overweight obesity and activity

EXECUTIVE SUMMARY

Childhood obesity and low physical activity both have serious implications for children's health. This report had twin objectives: to explore determinants of both obesity and low physical activity in young children. Included in the investigation of obesity is an assessment of whether it is linked to low physical activity. The report also examined the extent to which mothers were aware of their child being overweight or obese and whether they were concerned by this.

Research questions

• What potentially modifiable factors are associated with children's overweight and obesity?
• What potentially modifiable factors are associated with children's low activity levels?
• Do mothers recognise overweight in their child, and what factors are linked to better recognition?

Possible influences on children's overweight or obesity and activity levels

Two main sets of possible influence on children's overweight/obesity and activity levels were considered: (1) parental factors, and (2) family and neighbourhood factors that might limit a family's ability to pursue a healthy lifestyle.

Parental factors considered included mother's overweight and her modelling of active and sedentary behaviour; child health-related practices likely to be under the parent's control such as children's snacking on unhealthy foods or playing outdoors; and general patterns of parenting.

Family and neighbourhood factors considered included socio-economic characteristics and maternal health as well as factors that might have closer link with a healthy lifestyle, such as a mother's attitudes towards a healthy lifestyle; or the provision of green spaces.

The Growing Up in Scotland ( GUS) study

The report uses data from almost 3,000 children in the Growing Up in Scotland study, a large nationally representative cohort study. Families have been surveyed every year for six years, from sweep 1 when children were 10 months old to sweep 6, conducted during 2010/11 when children were aged almost 6 years old (around 5 years 10 months).

Measuring overweight, obesity and activity

Overweight or obesity was classified using BMI cut-offs derived from national population growth charts. At age 6:

• 22% of children were overweight (including obese)
• 9% of children were obese

Most of the overweight or obese children had been similarly classified two years previously, at age 4. Despite this "tracking" of overweight and obesity, there was considerable movement of children out of the overweight and obese groups over the two-year period. Half of children who had been obese at age 4 were no longer obese at age 6, although most were still overweight.

Physical activity and sedentary behaviour were measured using mothers' reports of their child's behaviour. Physical activity covered walking, organised sport and exercise and active play, at home and at school. Screen time (watching TV, and using computers or games consoles at home) was used as an indicator of sedentary behaviour. At age 6:

• 15% of children exercised for less than the recommended level of 60 minutes daily
• 31% of children had 3 or more hours screen time on a typical weekday

Children's physical activity and sedentary behaviour at earlier ages were related to physical activity and sedentary behaviour respectively at age 6, suggesting that such behaviour may become habitual at an early age.

Factors associated with children's overweight and/or obesity

Statistical models of physical activity and sedentary behaviour allowed for a number of influences to be controlled for simultaneously. Models also allowed for a standard set of controls. These were the child's gender, ethnicity, birthweight and family size. In respect of these standard controls for child characteristics and family size, all models found a significant effect of:

• higher birthweight on an increased likelihood of overweight or obesity
• being in a family with four or more children on a reduced likelihood of being overweight or obese.

The following parental factors were associated with a greater likelihood of the child being overweight and/or obese:

• mother's overweight or obesity (mothers who were overweight or obese were more than twice as likely as mothers of healthy weight to have obese children)
• frequent snacking on sweets or crisps at toddler age
• skipping breakfast
• not eating the main meal in a dining area of the home
• low parental supervision

The strong association between mothers' overweight or obesity and children's BMI classification has been well established elsewhere. It may reflect several influences including an inherited predisposition to put on weight, continuation of the same environmental influences that led to a mother being overweight, and shared mother-child health practices related to diet and exercise.

Snacking on crisps and sweets more than once a week was very common for GUS children when they were toddlers. The measure was useful as an indicator of children at lower risk (those who had snacks and crisps once a week or less frequently), rather than predicting higher risk of overweight and/or obesity. Skipping breakfast may reflect a more general association with poor dietary habits. Not eating the main meal in a dining area (either the kitchen, dining room or a combined living/diningroom) could indicate eating more unhealthy foods, perhaps under less parental control. Low parental supervision could reflect lower monitoring of a child's health-related behaviours and less protective behaviour to shield a child from possible health risks.

Many health-related practices suggested elsewhere as important for childhood overweight and obesity were not apparent in this study. These include shorter duration or absence of breastfeeding, early introduction of solids, soft drink consumption, fruit and vegetable consumption and use of convenience or fast food for the child's main meal. Low physical activity, high sedentary behaviour or short sleep duration did not predict increased risk of overweight or obesity.

Additional family and neighbourhood risk factors for healthy weight management were:

• poor maternal physical health
• low "child-friendliness" of the neighbourhood, based on mothers' assessments of the overall social and physical environment

The effect of poor maternal physical health requires further investigation, and could be linked to longstanding overweight in mothers. It seems unlikely that low child-friendliness is simply acting through constraints on physical activity, since children's activity levels as measured in GUS did not have clear associations with obesity. Further research is needed using objective measures of neighbourhood quality to see how they relate to mothers' perceptions.

Factors associated with children's low activity levels

Statistical models of physical activity and sedentary behaviour allowed for a number of influences to be controlled for simultaneously. These models also allowed for a standard set of controls. These were the season of the year and various child characteristics: gender, ethnicity and family size.

Risk factors for low physical activity were:

• a less physically active mother
• a less warm mother-child relationship
• mother thought children require less than 60 mins/day physical activity
• no nearby swimming pool

Risk factors for high screen time were:

• mother's high screen time
• TV in the child's bedroom
• fewer mother and child shared activities
• fewer parental rules to guide behaviour
• greater social deprivation
• poor quality local green spaces

More work is required to see whether objective measures of green space quality align with mothers' views, but it seems plausible that without attractive local green spaces, families may spend more time indoors using screen entertainment.

Mothers' recognition and concerns for a child's overweight

Most mothers with an overweight or obese child described their child's weight as "normal", with only 14% recognising their child as overweight. Mothers' recognition of overweight was improved if:

• their child was obese rather than overweight
• their child was a girl
• mothers were overweight or obese themselves

Mother's recognition of overweight was associated with greater concern for the child's weight. However, greater maternal recognition and concern at age 4 were not associated with child weight loss by age 6.

Strengths and limitations of the study

This study was able to examine a wide range of potential risk factors for overweight and/or obesity and low activity in a large sample of Scottish 6 year olds.

Most, but not all, potential risk factors were measured in previous sweeps. However, it is important to note that the associations found do not necessarily show causal relationships. Associations may be due to other confounding factors that have not been studied, including influences that pre-date the birth of the child and inherited effects.

Although children's and mothers' BMIs were based on researchers' measurements of weight and height, most measures, including those for activity, rely on mothers' reports. The study did not include some relevant information, including detailed dietary information for children and parents, mother's BMI measured at earlier time points, and partner's BMI.

Comparison with other studies

The study extends previous research on children's obesity using other cohort studies (such as the Millennium Cohort Study) by incorporating a wider range of children's health behaviours related to diet and exercise, as well as more information on parenting. While this study found no evidence for some risk factors identified elsewhere (such as maternal smoking, breastfeeding, short sleep duration and television viewing), several findings, such as the influence of maternal BMI and dietary practices, are consistent with previous work. The Growing Up in Scotland data also suggest that low parental supervision may contribute to children's obesity, although other general aspects of parenting did not show a clear association with overweight and obesity.

In terms of risk factors for low activity levels, the study found no evidence for some risk factors identified in other work, such as maternal overweight, but it echoed other research indicating the role of parental modelling of active or sedentary behaviour, bedroom TV (for high screen time) and aspects of general day-to-day patterns of parenting.

Policy implications

Many risk factors identified for young children's overweight and low activity are potentially modifiable, or would at least allow risk groups to be identified. The "tracking" of child overweight and activity from earlier ages suggests that early intervention may be most valuable.

The strong association between mother and child overweight, together with the importance of other parental factors, suggest that interventions to reduce child overweight and obesity may be most sucessful if they treat the family as a unit, rather than focusing exclusively on the child's weight. Improving mothers' recognition and concern for a child's overweight is likely to be only a first step in tackling the problem, since greater awareness may not translate into better weight management without addressing other aspects of parental behaviour. In terms of parenting, improving dietary practices and overall parental supervision appear to offer a promising approach.

For physical activity, there are also signs that interventions should be at the family rather than child level, to encourage parents and children to share a similar active lifestyle with a close parent-child relationship and structured behaviour management. Increasing mothers' awareness of desirable levels of physical activity for their children may also have a positive effect on parental encouragement and support for their child.

Better access to places where children can be physically active, including attractive green spaces, may increase activity levels and reduce sedentary behaviour. Further investigation is required to understand how the "child-friendly" aspects of the neighbourhood are associated with a lower level of child obesity.