Childhood obesity is one of the world's foremost current public health challenges. This challenge is particularly acute for Scotland, along with the UK as a whole, which has one of the highest levels of obesity amongst OECD countries (OECD, 2014).
The Growing Up in Scotland study (GUS) has collected data which provides a unique opportunity to further understand patterns of childhood overweight and obesity and to inform policy development.
This report explores rates of overweight and obesity amongst 10 year old children in Scotland and examines how these vary between children with different characteristics. It also investigates whether the level of overweight/obesity changes as the children grow older (from 6 to 10 years of age), and whether the changes are associated with the children's demographic and socio-economic characteristics. Uniquely, using the study's longitudinal data, the report illustrates how individual weight status changes - that is, what proportion of children move into or out of overweight/obesity between the age of 6 and 10 – and identifies the demographic, socio-economic and related characteristics associated with those changes.
In this report, children's BMI has been classified using the national BMI percentiles classification (Cole et al, 1990; Cole et al, 1998). The 85th / 95th percentile cut-off points are commonly accepted thresholds used to analyse children's overweight and obesity, respectively. The terms 'overweight (including obese)', 'overweight or obese' and 'overweight/obese' are used interchangeably throughout the report to describe children whose BMI was at or above the 85th percentile.
What proportion of children are overweight/obese at age 10, compared with age 6, and what proportion move into and out of healthy weight/overweight/obese categories during that period?
- Children are more likely to be overweight or obese at age 10 than age 6. At age 6, 24% of children were overweight including 11% who were obese. By age 10, 34% of children were overweight including 19% who were obese. On average, BMI had increased by 2.5 BMI points for all children over the period from age 6 to age 10.
- Most (79%) children who were a healthy weight at age 6 remained a healthy weight at age 10. However, around 12% became overweight and a further 8% became obese.
- Children already overweight or obese at age 6 were more likely to remain so or to see their BMI increase over the following four years than to see their BMI decrease. Amongst children who were overweight at age 6, 34% remained overweight and 33% became obese at age 10. Around 34% returned to a healthy weight.
- The vast majority (79%) of children who were obese at age 6 remained so at age 10. Thirteen percent became overweight and just 8% became a healthy weight.
- Even amongst those children who remained in the same BMI category at both ages, BMI increases are evident. For children who remained a healthy weight, BMI increased by an average of 1.4 points. For those who were overweight and those were obese at both time points BMI increased by 2.3 and 4.8 points respectively.
How does overweight/obesity vary amongst 10 year old children according to demographic and socio-economic characteristics and is there any change in the social gradient of overweight/obesity between age 6 and age 10?
- Between age 6 and age 10, rates of overweight and obesity increased similarly both for boys and girls, and for children of white and other ethnicities. For example, overweight/obesity amongst boys increased from 25% to 34% and amongst girls from 23% to 34%. There were no significant differences in the proportion of children overweight/obese by sex or ethnicity at any age point.
- Levels of overweight and obesity also increased amongst children with all types of social background.
- However, levels of overweight including obesity increased more amongst children in more disadvantaged groups than amongst children in more advantaged groups. As children in more disadvantaged groups were more likely to be overweight or obese at age 6, this means that inequality in levels of overweight and obesity according to social background widens between age 6 and age 10.
- For example, rates of overweight including obesity amongst children living in the 20% least deprived areas rose by just 3 percentage points from 22% at age 6 to 25% at age 10. In contrast, the proportion of children living in the 20% most deprived areas that were overweight including obese increased by 15 percentage points from 24% to 39%.
- Similarly, amongst children in the lowest income group overweight including obesity increased from 23% at age 6 to 36% at age 10 and for children in the highest income group from 20% to 29%.
What other factors are associated with overweight/obesity at age 10?
- Children whose mothers are overweight or obese are significantly more likely to be overweight or obese themselves at age 10 than children whose parents have a healthy BMI. For example, 29-32% of children whose mother was obese were also obese compared with 11% of children whose mother was a healthy weight.
- Higher typical screen time and irregular breakfast habits were associated with overweight/obesity. For example, 34% of children with between 14 and 21 hours per week of screen time were overweight or obese compared with 25% of children with less than 14 hours, and 31% of children who always ate breakfast were overweight or obese compared with 44% of those who only occasionally ate breakfast. Both factors also varied considerably by social background. For example, children in lower income households were more likely than those in higher income households to have higher screen time and irregular breakfast habits.
- Children with a television in their bedroom were more likely to be overweight or obese than those without – 38% compared with 26%. Having less than the recommended amount of sleep was also associated with overweight/obesity. Thirty-seven percent of children who had less than the recommended amount of sleep were overweight or obese at age 10 compared with 32% of those who had the recommended amount of sleep.
- Child longstanding illness, frequency of unhealthy snacking for children or parents, level of physical activity at age 6, participation in sport were not statistically significantly associated with child overweight/obesity at age 10.
- Thirty-five percent of parents whose children were obese and 88% of those whose children were overweight perceived them to be of normal weight. Children also misperceived their weight status: 63% of children who were obese and 78% of those who were overweight perceived themselves to be 'about the right size'.
- Children who were obese were less likely to be very happy about the way they looked than healthy weight children (53% compared with 62%). Differences in body satisfaction between children who were overweight and healthy weight were not statistically significant.
- Analysis was undertaken to explore which factors were most closely associated with being overweight or obese at age 10 when all factors of interest were taken into account. The results show that being overweight or obese at age 6, having a mother who was obese, an average weekly screen time of 14 hours or more, only occasionally eating breakfast and having a TV in the child's bedroom were all associated with being overweight/obese at age 10. Of these, BMI status at age 6 was by far the strongest predictor of overweight/obesity at age 10.
Which factors are associated with a move out of or a move into overweight and obesity between ages 6 and 10?
- Using a child's BMI status at age 6 and at age 10, a new variable was derived which captured transitions in BMI status between the two age points. This variable had the following categories:
- Remain healthy weight: children whose BMI was classified as healthy weight at both ages
- Move out of overweight: children who were overweight or obese at age 6 and healthy weight or underweight at age 10
- Move into overweight: children who were healthy weight or underweight at age 6 and overweight or obese at age 10
- Remain overweight: children who were overweight or obese at age 6 and age 10
- Other: children who were underweight at age 6 and age 10 or who moved between being underweight and healthy weight
- Fifty-eight percent of all children were a healthy weight at age 6 and age 10. Fifteen percent moved into overweight whilst 5% moved out of overweight. A significant minority (19%) remained overweight whilst 3% fell into the 'other' category.
- A higher proportion of children living in more deprived areas moved into overweight than did children living in less deprived areas. Seventeen percent of children living in areas in the most deprived quintile became overweight or obese compared with 11% of those living in areas in the least deprived quintile.
- Higher rates of moving into overweight were also seen amongst children whose mothers were obese, children who reported eating breakfast 'occasionally' or 'quite often' (rather than 'always'), those with higher weekly screen time and those with a TV in their bedroom. For example, 16% of children with a TV in their bedroom moved into overweight compared with 11% of those who did not have a TV in their bedroom.
- A greater proportion of children with heavier birth weights than those with lighter birth weights moved out of overweight. Higher rates of moving out of overweight were also seen amongst those who snacked on unhealthy items less frequently and children who did not have a TV in their bedroom. For example, 10% of children who ate unhealthy snacks up to once a day moved out of overweight compared with 4% of those who consumed unhealthy snacks more often.
- As previously, analysis was undertaken to explore which factors were most closely associated with moving into overweight when all factors of interest were taken into account. The results found that having a higher weekly screen time and a mother who was overweight or obese were statistically significantly associated with moving into overweight. The results also tentatively suggest that having a TV in the child's bedroom and not always eating breakfast may also be associated with moving into overweight, though the relationship was not statistically significant.
- Similar analysis was also undertaken to identify which factors were most closely associated with moving out of overweight. The results indicate that moving out of overweight was associated with lower household income, less frequent consumption of unhealthy snacks and not having a TV in the child's bedroom. The relationship with lower household income is opposite to that found in the other analysis where it has been associated with BMI increase. This may have occurred because a higher proportion of lower income children were overweight/obese at age 6 thus providing greater scope for a reduction in BMI amongst children in that group by age 10.
This report demonstrates a notable increase in rates of overweight and obesity in children between age 6 and age 10. Indeed, BMI increased by an average of 2.5 BMI points for all children over the four years. The findings also show that inequalities in levels of overweight/obesity between children from different social backgrounds – which already exist at age 6 – have widened by age 10. This makes subsequently reducing that inequality more difficult as children move into adolescence and through onto adulthood.
A key factor predicting overweight and obesity at age 10 was being overweight or obese at age 6. Similarly, the majority of children who were a healthy weight at age 6 were also a healthy weight at age 10. This suggests that addressing factors associated with being overweight in the early years and thus increasing the proportion of younger children of healthy weight would have a knock on effect, reducing levels of overweight in later childhood.
The findings further confirm existing evidence on some of the key influencing factors amongst children's day-to-day environments and experiences which may be modifiable in order to prevent and tackle increasing levels of overweight and obesity between early and middle childhood. These include mother's overweight/obesity, poor diet and inactivity including, particularly, a home environment which facilitates higher levels of inactivity. Parental recognition of child overweight/obesity is also problematic suggesting many parents are ill-informed or find it hard to recognise. Thus interventions to reduce child overweight and obesity would benefit from the involvement of parents and the wider family along with steps to address issues in the home environment.
Email: Ewan Patterson