Publication - Progress report

Growing up in Scotland: overweight obesity and activity

Published: 10 May 2012

Report describing the influences of parental factors and family and neighbourhood factors on childrens's weight and sedentary behayiour.

Growing up in Scotland: overweight obesity and activity
CHAPTER 3 OVERWEIGHT AND OBESITY

CHAPTER 3 OVERWEIGHT AND OBESITY

3.1 Key findings

  • 22% of children were overweight (including obese), 9% were obese.
  • Risk factors for children's overweight and obesity include child characteristics (higher birthweight), maternal characteristics (high BMI and poor physical health), neighbourhood characteristics (low child friendliness), dietary practices and low parental supervision
  • Children who were overweight and obesity at age 6 were very likely to have been classified as overweight or obese at age 4
  • Physical activity and sedentary behaviour were not clearly associated with children's overweight and/or obesity

3.2 Prevalence and tracking of children's overweight and obesity

3.2.1 Prevalence of overweight and obesity at age 6

Reliable height and weight measurements were obtained from 3035 children (96% of the eligible sample at sweep 6). Following standard procedures developed by ISD Scotland, children with BMI values more than three standard deviations from the mean population value were excluded ( n=43, 1%), leaving 2992 cases.

Of these, three-quarters (76%) had BMI in the healthy range, 22% were overweight including obese, consisting of 13% who were overweight but not obese, and 9% who were obese or morbidly obese (Figure 3.1). It is not possible to make a precise comparison of these figures collected in 2010-11 for GUS children approaching their sixth birthday with the prevalence of children's overweight and obesity measured in the 2010 Scottish Health Survey, SHeS (Gray and Leyland 2011), as the SHeS does not provide a detalied breakdown by age. SHeS data found that 26% of children aged 2-6 years were overweight (including 11% obese), while 31% of children aged 7-11 years were overweight (including 18% obese).

Figure 3.1 Children's BMI classification at sweep 6

Figure 3.1 Children's BMI classification at sweep 6

Note: Numbers above each histogram show estimated percentage in each BMI category, with error bars indicating 95% confidence intervals. N values for number of cases in each BMI category are unweighted values. n=2992

The prevalence of overweight (including obesity) at age 6 (22%) was slightly reduced from that at age 4 (26%). However, the prevalence of obesity was similar at both ages (see Figure 3.2).

Figure 3.2 Prevalence of children's overweight and obesity at ages 4 and 6

Figure 3.2 Prevalence of children's overweight and obesity at ages 4 and 6

Note: Numbers above each histogram show estimated percentage in each BMI category, with error bars indicating 95% confidence intervals.

3.2.2 Association between overweight/obesity and children's height

Figure 3.3 shows that there was a strong association between height and overweight or obesity, with taller children more likely to be classified as obese or overweight. Other research has recognised this association, and considered whether the BMI measure might be misclassifying taller children (Freedman et al. 2003). However, this work found that taller children had greater skinfold thickness and raised insulin levels, and that childhood BMI was more strongly linked with adult adiposity than alternative indices relating height and weight measurements. The researchers concluded that BMI was more useful than alternative ways of relating weight and height measurements, and that the association between children's height and BMI does indeed reflect greater adiposity in taller children.

Figure 3.3 Association between children's height and overweight or obesity

Figure 3.3 Association between children's height and overweight or obesity

3.2.3 Tracking of overweight and/or obesity

This section examines associations between children's overweight/obesity at age 4 and obesity/overweight two years later, referred to as "tracking" of overweight and/or obesity.

The vast majority (90%) of children classified as healthy weight at age 4 remained in this category two years later (Table 3.1), with only 8% becoming overweight or obese. There was considerable tracking of overweight and/or obesity, in that children who were overweight or obese at age 4 were much more likely than healthy weight children to have weight problems two years later. However, there was considerable movement out of the overweight and obese categories over the two-year period.

Overall, 60% of children classified as either overweight, obese or morbidly obese at age 4 (combining three columns of Table 3.1) were also overweight or obese at age 6, but 40% became of healthy weight. Almost half (48%) of children classified as either obese or morbidly obese at age 4 (combining two columns of Table 3.1) were similarly classified at age 6, 37% were reclassified as overweight and 15% became a healthy weight.

Table 3.1 Association between children's BMI at age 4 and age 6

Age 4 BMI classification
Underweight Healthy weight Overweight Obese Morbidly obese Bases
Age 6 BMI classification % % % % % Wtd Uwtd
Underweight 25 2 - - - 47 47
Healthy weight 75 90 54 21 8 2069 2136
Overweight - 6 31 45 25 351 369
Obese - 1 6 14 21 103 109
Morbidly obese - 1 9 20 47 137 120
Total 100 100 100 100 100 2707 2781

3.3 Exploration of child and family factors associated with children's overweight and obesity

Important note: From this point forward, the term "overweight" is used to include all children at or above the 85th BMI percentile ( i.e. including those who were obese or morbidly obese). The term "obese" includes all children at or above the 95th BMI percentile ( i.e. including those who were morbidly obese).

Associations between individual child and family characteristics and children's overweight and obesity were explored (Table 3.2). Note that these associations do not take account of other factors that simultaneously may play a role.

Greater birthweight (standardised for gender, gestation and parity) was strongly associated with being overweight or obese at age 6. Neither gender, ethnicity, birth order or number of siblings was clearly associated with being overweight or obese, although there was a trend for children from larger families to be at lower risk. The GUS sample contains only a small percentage of children from ethnic minority groups, so is not as well placed to explore ethnic differences in overweight and obesity as the Millennium Cohort Study, which has a boosted ethnic sample.

Table 3.2 Child and family characteristics: associated with with children's overweight and obesity at age 6, bivariate analyses

% overweight or obese p % obese p Bases
Wtd Uwtd
Gender Male 23 NS 8 NS 1502 1521
Female 22 10 1433 1471
Ethnicity White 22 NS 9 NS 2814 2892
Minority group 20 11 120 99
Birthweight (standardised) 1 - lowest decile 12 *** 7 ? 325 300
2 14 6 311 298
3 15 7 300 293
4 23 12 294 303
5 23 8 289 295
6 23 9 292 301
7 25 11 288 302
8 26 9 283 299
9 32 14 269 296
10 - highest decile 32 11 279 298
Birth order First born 23 NS 9 NS 1472 1445
Not first born 21 9 1463 1547
Number of children in household One 25 ? 11 ? 585 552
Two 22 9 1538 1643
Three 22 9 621 635
Four or more 14 5 192 162

Notes: p=probability of difference between groups based on adjusted F where NS=not significant, † p<0.1, * p<0.05, ** p<0.01, *** p<0.001.

3.4 Exploration of parental factors associated with children's overweight and obesity

There were a number of statistically significant associations ( p<0.05) between individual parental factors and children's overweight and/or obesity, shown in Table 3.3. Note that these associations do not take account of other possible confounding influences. Significant associations with children's overweight and/or obesity included:

  • Mother's overweight or obesity
  • Nutritional practices related to
    • Infant nutrition including duration of breastfeeding and the timing of solids
    • Frequency of consumption of sweets and crisps as a toddler (age 2)
    • Eating the main meal in a room without a dining area (ages 2 and 5)
    • Skipping breakfast (age 5)
    • Use of a local take-away (age 6)
  • Sedentary behaviour related to
    • TV in the child's bedroom
    • Screen time from sweep 4 onwards
  • Low levels of parental supervision

Parental factors that were not significantly associated with children's overweight and/or obesity at age 6 are not shown in Table 3.3. These included parental sedentary behaviour and exercise, children's pattern of eating at age 2 (snacking between meals, composition of snacks), children's fruit and vegetable consumption, children's soft drink consumption, children's frequent eating of sweets and crisps at age 5, frequent use of a take-away, restaurant or convenience food for main meal at ages 3 and 5, children's physical activity, children's sleeping duration, patterns and problems; as well as most aspects of general patterns of parenting including warmth, joint parent-child activities, rules, household chaos and conflict.

Table 3.3 Parental factors associated with children's overweight and obesity at age 6, results of bivariate analyses

% overweight p % obese p Bases
Wtd Uwtd
Parental example
Mother's BMI (sweep 6) Underweight or healthy 16 *** 5 *** 1147 1200
Overweight 22 10 808 845
Obese 29 14 619 606
Health-related practices - nutrition
Breastfeeding duration (age 1) None 24 NS 11 *** 1147 973
<4 months 21 8 1210 1329
4 months plus 20 6 578 689
Introduction of solids (age 1) <4 months 28 ** 12 ? 434 384
4 months or later 21 9 2498 2603
Crisps - frequency (age 2) Once a week or less 17 * 5 * 538 585
More than once a week but not every day 23 9 1079 1139
Daily 24 11 975 966
More than once daily 24 10 342 301
Sweets - frequency (age 2) Once a week or less 17 * 4 ** 628 685
More than once a week but not every day 24 10 1070 1136
Daily 22 11 888 870
More than once daily 25 10 347 299
Where child eats main meal (age 2) Kitchen/dining room/combined living and dining room 20 * 8 * 1784 1994
Other room (living room, bedroom, other) 25 11 1031 880
Eats breakfast (age 5) Yes 22 ? 9 *** 2791 2860
No 29 19 144 131
Where child eats main meal (age 5) Kitchen/dining room/combined living and dining room 20 *** 8 *** 1901 2109
Other room (living room, bedroom, other) 27 13 928 793
Use of local take-away/fast food outlet (age 6) I don't use it 16 * 7 NS 314 345
I use it sometimes 23 10 2046 2073
I use it often 22 8 364 330
There isn't one in this area 22 7 211 243
TV in bedroom (age 4) Yes 24 * 10 * 1332 1180
No 21 8 1574 1783
TV in bedroom (age 5) Yes 25 *** 11 *** 1512 1368
No 19 7 1414 1613
Weekday TV time (age 4) None 21 * 9 * 152 165
Up to 30 minutes 16 6 78 84
30 minutes to 1 hour 21 9 155 170
1 to 2 hours 21 8 1120 1189
2 to 3 hours 25 11 843 852
3 to 4 hours 21 7 319 297
4 to 5 hours 21 9 130 115
5 or more hours 34 17 104 86
Weekday screen time (age 5) Under 1 hour 20 * 8 NS 279 314
1 to under 2 hours 19 8 876 956
2 to under 3 hours 22 9 904 918
3 to under 5 hours 26 11 691 656
5 hrs plus 23 13 157 125
Weekday screen time (age 6) Under 1 hour 19 * 8 ? 190 212
1 hr to under 2 hours 19 7 734 803
2 hrs to under 3 hours 24 9 744 757
3 hrs plus 25 11 763 698
General patterns of parenting
Supervision (age 4) Low 27 * 15 *** 568 534
Medium - low 21 8 923 908
Medium - high 21 7 1015 1065
High 21 9 430 485

Notes: p=probability of difference between groups based on adjusted F where NS=not significant, † p<0.1, * p<0.05, ** p<0.01, *** p<0.001.

3.5 Exploration of family and neighbourhood constraints associated with children's overweight and obesity

Distal (background) family and neighbourhood constraints on children's healthy weight identified as having statistically significant individual associations with children's overweight and/or obesity at sweep 6 (see Table 3.4 and Table 3.5) included:

  • Lower maternal education (below HNC/ HND)
  • Biological father not present in household
  • Bottom 40% of average household income
  • Poor maternal physical health over sweeps 1, 3 and 5
  • Maternal smoking (pregnancy, sweep 1)
  • Area deprivation (two most deprived quintiles)

These findings suggest social inequalities in the patterning of children's overweight and obesity. As in the previous section, note that these associations do not take account of possible confounding influences.

Other possible family and neighbourhood constraints examined (mother's working hours, mother's mental health and urban-rural area) were not clearly associated with children's overweight and obesity (and are not included in Table 3.4 and Table 3.5).

Proximal family and neighbourhood constraints significantly associated with children's overweight and obesity (see Table 3.4 and Table 3.5) included:

  • Cost affecting mother's preparation of food (age 5, but not age 2)
  • Mother's feelings of personal safety when out alone by day and night (age 4 but not age 6)
  • Child-friendliness of neighbourhood (age 4, but not age 6)
  • Antisocial behaviour problems in neighbourhood (age 6)

Proximal family factors that did not show clear protective effects in helping to prevent children's overweight or obesity included mothers' views on desirable levels for children's physical activity and concerns for the child's weight.

Proximal neighbourhood factors not clearly asociated with children's overweight and/or obesity (and not shown in Table 3.4 and Table 3.5) included access to local facilities such as a garden, playpark, local swimming pool or green space and the quality or safety of playparks.

Table 3.4 Family constraints associated with children's overweight and obesity at age 6, results of bivariate analyses

% overweight or obese p % obese p Bases
Wtd Uwtd
Distal family factors
Mother's education Up to Standard Grades or equivalent 23 * 11 ** 1104 936
Higher Grades or equivalent 25 11 649 669
Upper level VQs ( e.g. HNC, HND) 20 7 370 400
Degree or equivalent 19 6 805 980
Biological father in household (ages 1-5) Not present throughout 25 ? 12 ** 850 640
Present throughout 21 8 2086 2352
Household income (equivalised, average quintile, ages 1-5) Top 60% 21 NS 7 ** 1499 1784
Bottom 40% 23 11 1421 1194
Mother's physical health (ages 1,3 and 5) Poor 26 ** 11 ** 995 980
Medium 22 9 1003 1022
Good 19 7 929 984
Smoked in pregnancy No 22 NS 8 ** 2222 2396
Yes 24 12 703 586
Proximal family factors
Mother affected by food costs (age 5) A lot 29 NS 19 * 94 74
A fair amount 24 11 251 242
A little 23 9 881 899
Not at all 21 8 1710 1777

Notes: p=probability of difference between groups based on adjusted F where NS=not significant, † p<0.1, * p<0.05, ** p<0.01, *** p<0.001.

Table 3.5 Neighbourhood constraints associated with children's overweight and obesity at age 6, results of bivariate analyses

% overweight or obese p % obese p Bases
Wtd Uwtd
Distal neighbourhood factors
Area deprivation ( SIMD quintile) 1 least deprived 20 NS 7 * 576 697
2 20 7 615 706
3 22 8 566 618
4 26 11 552 511
5 - most deprived 23 12 627 459
Proximal neighbourhood factors
Neighbourhood safety (age 4) High 22 NS 8 ** 1886 2021
Low 23 11 1049 970
Child friendly neighbourhood (age 4) Good 20 * 8 ** 1102 1238
Average 23 7 760 795
Poor 24 12 1073 958
Antisocial behaviour in area last year (age 6) None 22 NS 8 * 1503 1638
One 21 8 625 640
Two 22 9 295 296
Three 22 8 197 183
Four or more 25 15 312 233

Notes: p=probability based on adjusted F where NS=not significant, † p<0.1, * p<0.05, ** p<0.01, *** p<0.001.

3.6 Multivariate modelling of factors associated with children's overweight and obesity at age 6

More sophisticated analyses examined associations between parenting, family and neighbourhood factors and children's overweight and/or obesity, controlling for various factors simultaneously. This section reports the main findings of multivariate analyses using logistic regression models of children's overweight (including obese) and obese at age 6. Detailed results are provided in the Technical Appendix. The reference group for the model of overweight was all children with healthy weight plus the small number of underweight children. In the obesity model, this reference group in addition included overweight children.

Several of the potential risk factors were highly correlated with one another. These included TV in bedroom with high screen time, consumption of crisps with consumption of sweets, child-friendliness of neighbourhood with low perceived safety and antisocial behaviour problems, and eating in a room not primarily designed for food consumption with use of a local takeaway. Exploratory models to assess the strength of different effects was used to guide further selection of variables for the multivariate models. Bedroom TV, child-friendliness of the neighbourhood and eating in a room without a dining area were selected 11 . Snacking on sweets and crisps were combined to create a composite measure of snacking on both foods.

Children's overweight and obesity at age 4 was not included in the models, although as section 3.2.3 showed, children's BMI classification at age 4 was a very strong predictor of overweight and obesity two years later. 12

All modelling controlled for the child's gender and their age in months at the sweep 6 interview, ethnic group, birthweight, and number of children in the family. 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

There were no statistically significant differences in overweight or obesity according to the child's gender, age at sweep 6 interview or ethnic group (white/minority).

Various stages of modelling looked at the separate influences of parenting and of family and neighbourhood constraints (see the Technical Appendix for details). A combined model was then used to examine all factors simultaneously. In this combined model the following factors emerged as significantly associated with children's overweight and obesity (summarised in Figure 3.4):

  • Mother's overweight or obesity
  • Frequency of sweet and crisp consumption as a toddler
  • Mother's poor physical health

Additional factors associated with children's overweight (including obesity) were:

  • Eating main meal in a room without a dining area

Additional factors associated with children's obesity were:

  • Low parental supervision
  • Skipping breakfast
  • Low child-friendliness of neighbourhood

Figure 3.4 Summary of risk factors for children's overweight and/or obesity at sweep 6: results of final multivariate modelling

Figure 3.4 Summary of risk factors for children's overweight and/or obesity at sweep 6: results of final multivariate modelling

Note: Shaded areas indicate increased or decreased risk of either overweight and obesity, or obesity. Model adjusted for all factors together, see Tables 1.1 and 1.2 in the Technical Appendix for further details


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