January 26, 2023

expert reaction to study looking at the UK sugary drinks tax and obesity in children

A study published in PLOS Medicine looks at trajectories of obesity prevalence in English primary school children and the UK soft drinks industry levy.

Prof Emma Frew, Professor in Health Economics, Centre for Economics of Obesity, University of Birmingham, said:

“The press release accurately reflects the science.  It is high-quality research – it uses a national representative sample of over 1 million children each year in England.  The UK government implemented the Soft Drinks Industry Levy in April 2018 to tackle childhood obesity.

“With this large-size and unique dataset, this is the first to suggest the levy is working as part of a wider obesity prevention plan to reduce the rise in obesity in 10 to 11 years girls in England, especially among those in the most deprived areas.  This finding means that the implementation of levy should be an essential part of an obesity prevention strategy although further research is needed to understand why we see an impact in girls but not in boys.”

Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“This paper analysed data from the National Child Measurement Programme (NCPM) which collects data annually in the school year from primary schools.  The authors used the year 2013/14 as a baseline and then compared the trend for change in obesity with time up until November 2019.  The soft drink levy became law in April 2018 but many drink manufacturers had reformulated to a lower sugar content before the deadline.  The authors suggest there was some evidence for an association with the rate of increase in obesity to be significantly lower in year 6 girls but not boys associated with the period surrounding with the introduction of the soft drink levy using  2013-14 as baseline.  However, the prevalence of obesity was about 6% higher in year 6 boys.  The claim that the soft drink levy might have prevented 5000 children from becoming obese is speculative because it is based on an association not actual measurements of consumption.

“Overall the annual reports from NCPM show no evidence for any decrease in obesity in reception year children, instead they show a slight increase (https://commonslibrary.parliament.uk/research-briefings/sn03336/) and the authors acknowledge this age group are not big consumers of sugar sweetened beverages.  The average rates of obesity for reception 2010-2014 were 9.4% and 9.7% just before COVID.  The corresponding rates in year 6 children were 19.0% and 20.2%.  The COVID epidemic had a huge impact on obesity rising to 14.4% in reception year and 25.5% in year 6 in the 2020-21 school year and the preliminary data for 2021-22 show some falls but they are still higher than in 2010-2014, being 10.4% in reception year and 23.5% in year 6.

“Obesity has consistently been higher in year 6 boys than girls (currently 26.5% % in boys and 20.3% in girls).  Arguably the impact of the soft drinks levy would be expected to be greater in boys as they are bigger consumers of soft drinks.  Also children from the poorest households would be expected to be impacted by the price increase caused by the soft drink levy.  The paper provides some evidence that this may have been the case for girls but not boys.  The children most likely to become obese, particularly during the COVID epidemic, were from the poorest households and the increase was greater in boys than girls.  There are lesson to be learnt from the epidemic.  As well as continuing to discourage the consumption of sugar sweetened beverages and sweets, wider recognition should be given to foods such as biscuits, deep fried foods (crisps, cornsnacks, chips) that make bigger contribution to excess calorie intake in children.  Tackling poverty, however, is probably best way to improve the diets of socially deprived children.”

Dr Simon Steenson, Nutrition Scientist, British Nutrition Foundation, said:

“Living with obesity can have a huge impact on a child’s physical and mental health.  Overweight and obesity in childhood can mean a greater chance of excess weight that continues into adolescence and adulthood, increasing the risk for type 2 diabetes, heart disease, and some types of cancer.  Weight stigma can also be damaging to the mental health of children living with obesity.

“This new study comes from a research group with an established track record in public health research, and provides an important insight into the potential effectiveness of the Soft Drinks Industry Levy implemented in April 2018 as a part of the government’s broader childhood obesity strategy.

“The finding that introduction of the tax was associated with over 5,000 fewer cases of obesity in girls aged 10-11 years is an encouraging sign, especially as this difference between the measured and predicted levels of obesity was greatest among girls attending schools in the most-deprived areas.  We know that there are well-established health inequalities in childhood obesity, with the same dataset used by the authors showing that Reception and Year 6 children from the most deprived areas of England are over twice as likely to be living with obesity as those from the least deprived areas.

“However, the underlying causes of obesity are complex and so it is difficult to directly attribute a change in obesity levels to a single factor.  For example, the announcement and implementation of the sugar tax occurred alongside a programme of voluntary sugar reduction in other products commonly consumed by children, including biscuits, breakfast cereals, yogurts, and confectionery.  The authors have importantly highlighted that there are limitations to the interpretation of their study, which only shows an association rather than a causal link.

“It is hard to discount a potential influence of changes to the availability of free sugars across these other food categories, especially among groups where these foods are more commonly consumed than sugar-sweetened beverages.  For example, data from the National Diet and Nutrition Survey shows that the proportion of children drinking sugar-sweetened beverages fell by 44 percentage points for those aged 4 to 10 years, and by 25 percentage points for 11-to-18 year-olds, between 2008/09 and 2018/19.

“An important point made by the authors is that the number of avoided cases of obesity that they reported only reflects a ‘dampening’ of the rate of increase in obesity among children, and not a reversal of current trends.  Therefore, it remains important that multi-component strategies continue to be implemented to increase access to affordable healthier foods, especially among children from low-income households, and to support greater physical activity.  This will require combined action from stakeholders across the public and private sectors, from the national to local levels, if we are to improve the health of the UK’s children.”

The following comment was provided by our colleagues at SMC Spain:

María Dolores del Castillo, researcher at the Food Science Research Institute (CSIC-UAM), Spain, says:

“In 2015, the World Health Organization (WHO) recommended implementing measures worldwide to reduce the consumption of sugary drinks and their health consequences. WHO reports suggest that taxes on sugary drinks help reduce the consumption of these products and also the prevalence of obesity, type 2 diabetes and dental caries. However, the results derived from different studies of the implementation of this policy in different countries indicate controversial results. Therefore, the results of this publication are of great interest in order to obtain information to establish the effectiveness of policies that are being implemented globally to reduce sugar intake and the incidence of childhood obesity and chronic diseases in the future.

“The authors use data from the National Child Measurement Programme that began in 2006. The height and weight of primary school children aged 4 and 5 years and 10 and 11 years, respectively, were measured annually. The study was conducted to find out the levels of overweight and obesity in children. In 2016, a tax was imposed on sugary soft drinks in the UK. The authors examined the prevalence of obesity in selected populations for 19 months after the implementation of this measure. The effect of gender and household socio-economic status on childhood obesity was also assessed. The study concludes that the levy reduced the prevalence of obesity only in sixth-grade girls (10-11 years) living in areas with the worst economic conditions of those studied.

“The results found by the authors indicate that the variables studied influence the outcome in line with previous studies. Not surprisingly, differences due to age and gender are found. The authors describe the strengths and limitations of the study and compare their results with similar studies. However, the size of the populations for each sex and age group is not clearly specified. Prevalence is mentioned and percentage data are given. There is no indication of how many pre-school or primary school children of each economic status participated in the study. Similarly, there is no indication of how the level of consumption of sugar-sweetened beverages by the populations studied has been assessed.

“These factors could have an influence on the result to be taken into account in the interpretation of the results. Another aspect that could influence the result and has not been taken into account are the differences in the degree of hormonal development of the two groups of girls and boys. The girls in the sixth grade group may be past menarche, which may influence food intake and metabolism. As the authors acknowledge, further research is needed to understand the effectiveness of the sugar rate, but it is imperative to continue to emphasise the reduction of sugar intake in the whole population and most importantly in children and adolescents.”

‘Associations between trajectories of obesity prevalence in English primary school children and the UK soft drinks industry levy: An interrupted time series analysis of surveillance data’ by Nina T. Rogers et al. was published in PLOS Medicine at 19:00 UK time on Thursday 26 January 2023.

DOI: 10.1371/journal.pmed.1004160

Declared interests

Prof Emma Frew: “Member of Strategic Council All-Party Parliamentary Group on Obesity.  No other COIs.”

Prof Tom Sanders: “No conflicts of interest in the last 3 years.”

Dr Simon Steenson: “Funding to support the British Nutrition Foundation’s charitable aims and objectives comes from a range of sources including membership, donations and project grants from food producers and manufacturers, retailers and food service companies, contracts with government departments; conferences, publications and training; overseas projects; funding from grant providing bodies, trusts and other charities.  Further information about the British Nutrition Foundation’s activities and funding can be found at http://www.nutrition.org.uk/aboutbnf/.”

María Dolores del Castillo: “No conflicts.”