Friday January 30 2015
Obese children tend to grow up to be obese adults
"The rise in childhood obesity … may be beginning to level off," BBC News reports. Researchers examined trends in child and adolescent rates of overweight and obesity using electronic GP records from 1994 to 2013.
The data shows there was a significant increase in child and adolescent overweight and obesity rates every year during the first decade from 1994 to 2003. Overall, annual rates did not increase significantly during the second decade, 2004 to 2013.
However, when split by age category, the results showed there was still a significant upward trend in overweight and obesity rates for the oldest age group (11 to 15 years) – albeit with less of an increase than there was in the first decade. At its maximum in recent years, overweight and obesity has affected almost two-fifths of adolescents in this age group.
As the researchers used GP records, it is possible children who have problems with their weight and were assessed by their GP are over-represented. This could then lead to an overestimate of prevalence. However, it is hard to think of another method of analysis that would provide a more reliable estimate.
While it is encouraging to see that the child obesity epidemic is not getting worse, there are also no clear signs as yet that it's getting any better. Underlying factors, such as low activity levels and easy access to calorie-rich, nutrient-poor foods, still remain to be addressed.
Where did the story come from?
The study was carried out by researchers from King's College London, and was funded by the National Institute of Health Research (NIHR) Biomedical Research Centre at Guy's and St Thomas' NHS Foundation Trust and King's College London.
It was published in the peer-reviewed BMJ group publication, Archives of Disease in Childhood. The article is available on an open access basis, so it is free to read online or download.
Overall, the UK media coverage is generally accurate, though sources have a different take on the research – some pointing out the good news, others the bad.
The Daily Mail's statement that the "crisis at its worse among 11 to 15-year-olds" is not wholly accurate. While overweight and obesity rates in this age group have still increased in the past decade, it has been to a lesser extent than previously. It is also difficult to say that now is the "crisis point" as such, as we don't know what's going to happen in the future.
What kind of research was this?
This was a population-based cohort study that aimed to use GP electronic health records in England to examine the prevalence of overweight and obesity in children and adolescents aged 2 to 15 years. Researchers looked at data from 1994 to 2013 to see how trends have changed over the past two decades.
Obesity has become a significant public health issue in both adults and children, with rates in children known to have increased dramatically over past decades.
However, the researchers say there have been recent reports suggesting that obesity levels in children may have levelled off. That is what this study aimed to look at.
The main limitation of such a study is being able to sample a group of children that represent a fair picture of the child population as a whole.
Being based on database records, the study is not going to have information, or up-to-date information, on all children and adolescents. However, it should give a good representation of general trends.
What did the research involve?
The research used information from the Clinical Practice Research Datalink (CPRD), a large database holding the electronic health records of about 7% of general practices in the UK – about 5.5 million people. The coverage of GPs in the database was reported to be broadly representative of geographic distribution in the UK.
The CPRD contains information on weight, height and body mass index (BMI) where this has been collected. Only the first BMI recording for a child was taken for any given year, though an individual child could contribute several years' worth of data.
The final analysis included data from 370,544 children who contributed 507,483 BMI observations across the two study decades (average 1.4 BMI observations per child).
The researchers analysed BMI by sex and by three different age groups (2 to 5 years, 6 to 10 years, and 11 to 15 years). They looked at trends over the two decades 1994 to 2003, and 2004 to 2013. Thirty-nine per cent of the collected data came from the first decade, 61% from the second.
What were the basic results?
The prevalence of children who were either overweight or obese ranged as follows:
- 2-5-year-old boys – minimum 19.5% prevalence in 1995, to maximum prevalence 26.0% in 2007
- 6-10-year-old boys – minimum 22.6% in 1994, to maximum 33.0% in 2011
- 11-15-year-old boys – minimum 26.7% in 1996, to 37.8% in 2013
- 2-5-year-old girls – minimum 18.3% in 1995, to maximum 24.4% in 2008
- 6-10-year-old girls – minimum 22.5% in 1996, to maximum 32.2% in 2005
- 11-15-year-old girls – minimum 28.3% in 1995, to maximum 36.7% in both 2004 and 2012
Looking at annual trends, there was a clear year by year increase in prevalence of overweight and obesity in the first decade (1994 to 2003), with less of an annual increase in the second decade (2004 to 2013).
Looking at the odds of a child being overweight or obese, the annual increase in risk across every year of the study was 4.2%.
However, when broken down by decade, the annual risk increase was 8.1% between 1994 and 2003, but only 0.4% between 2004 and 2013.
The increase in risk of overweight or obesity each year was significant in the first decade, but not in the second. The researchers say this indicates overweight and obesity rates are stabilising. These trends were similar with separate analyses for both boys and girls.
When looking at trends per age category, the risk of overweight and obesity increased significantly every year for all age groups in the first decade between 1994 and 2003.
During the second decade, the risk of overweight and obesity did not increase significantly each year for the two younger age groups.
However, for the oldest age group (11 to 15 years), there was still a significant annual increase in risk of overweight and obesity during the second decade (by 2.6%), though this was still much smaller than the annual increase in the first decade (12%).
When looking specifically at obesity, all trends were comparable to those for the combined category of overweight and obesity as outlined above.
How did the researchers interpret the results?
The researchers say the use of GP electronic health records in England may provide a valuable resource for monitoring trends in obesity.
They say that, "More than a third of UK children are overweight or obese, but the prevalence of overweight and obesity may have stabilised between 2004 and 2013."
This research shows how trends in child and adolescent overweight and obesity have changed over the two decades from 1994 to 2013, as indicated by GP records.
As the results show, for both boys and girls, the prevalence of overweight and obesity increases with increasing age category, with the highest prevalence recorded in the 11 to 15-year-old age group, which at its maximum has affected almost two-fifths of adolescents in recent years.
However, it is encouraging to see that while there were significant annual increases in child overweight and obesity rates in the first decade between 1994 and 2003, the overall annual increase was not significant during the second decade, 2004 to 2013.
But when split by age category, it does show there was still a significant upward trend in overweight and obesity rates for the oldest age group (11 to 15 years), albeit with less of an increase than there was in the first decade.
Therefore, as the researchers say, this still highlights the need for interventions to address overweight and obesity, particularly for this adolescent age group.
An important limitation to be aware of for this study, though, is the possibility of selection bias. The study has used a large GP electronic database holding height and weight information for more than 350,000 children in the UK. It needs to be considered how representative this sample may be of the general child and adolescent population the UK.
While the database does contain a representative sample of GP practices and their registered population, not all UK children in these age groups will have been to the GP and had their height and weight measured.
There is the possibility a child may have been more likely to have their height and weight measured (particularly in successive years) if there have been problems with their weight.
As such, it is possible the database could be over-representative of children with weight issues, and so give an overestimate of the prevalence of overweight and obesity in the general child and adolescent population of the UK.
But accessing reliable data that is representative of every person is clearly not feasible, and using a reliable GP electronic database should give us a reasonable indication of the likely prevalence in the UK.
Such a study also can only provide us information on trends. It can't tell us the reasons that may be behind these changing trends, or tell us of future ones.
While the results suggest overweight and obesity levels may be levelling off (at least among the younger age groups), this is not to say they will now start to decrease. There have been annual decreases in the past, for example, that weren't sustained.
Overweight and obesity levels could still remain at these relatively high levels of around a third of all children and adolescents, or increase further again unless things change.
These results may give some encouragement, but childhood overweight and obesity remains an important public health issue. The various possible influences of overweight and obesity, such as low activity levels and consumption of calorie-dense food and drink, still need to be addressed.
The study is likely to lead to further calls by public health campaigners for the introduction of legislation designed to tackle childhood obesity, such as a curb on advertising and a tax on unhealthy foods.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.