The introduction of the soft drinks industry levy (SDIL) – dubbed the 'sugar tax' – in England was followed by a drop in the number of older primary school girls succumbing to obesity, according to researchers from the Universities of Cambridge, Oxford, and Bath, with colleagues at the London School of Hygiene and Tropical Medicine.
The study, published in PLOS Medicine, has led to calls to extend the levy to other unhealthy foods and drinks.
Obesity has become a global public health problem, the researchers said. In England, around 10% of 4- to 5-year-old children and 20% of 10- to 11-year-olds were recorded as obese in 2020. Childhood obesity is associated with depression in children and the adults into which they maturate, as well as with serious health problems in later life including high blood pressure and type 2 diabetes.
In the UK, young people consume significantly more added sugars than is recommended – by late adolescence, typically 70g of added sugar per day, more than double the recommended 30g. The team said that sugar-sweetened beverages (SSB) are the primary sources of dietary added sugars in children, with high consumption commonly observed in more deprived areas where obesity prevalence is also highest.
Protecting Children From Excessive Sugar
The two-tier SDIL on drinks manufacturers was implemented in April 2018 and aimed to protect children from excessive sugar consumption and tackle childhood obesity, by incentivising reformulation of SSBs in the UK with reduced sugar content.
To assess the effects of SDIL, the researchers used data from the National Child Measurement Programme on over 1 million children at ages 4 to 5 years (reception class) and 10 to 11 years (school year six) in state-maintained English primary schools. The surveillance programme includes annual repeat cross-sectional measurements, enabling the researchers to examine trajectories in monthly prevalence of obesity from September 2013 to November 2019, 19 months after the implementation of the SDIL.
Taking account of previous trends in obesity levels, they estimated both absolute and relative changes in obesity prevalence, both overall and by sex and deprivation, and compared obesity levels after the SDIL with predicted levels had the tax not been introduced, controlling for children's sex and the level of deprivation of their school area.
Although they found no significant association with obesity levels in reception age children or year six boys, they noted an overall absolute reduction in obesity prevalence of 1.6 percentage points (PPs) (95% confidence interval (CI): 1.1, 2.1) in 10-11-year-old (year 6) girls. This equated to an 8% relative reduction in obesity rates compared with a counterfactual estimated from the trend prior to the SDIL announcement in March 2016, adjusted for temporal variations in obesity prevalence.
The researchers estimated that this was equivalent to preventing 5234 cases of obesity per year in this group of year six girls alone.
Obesity Reductions Greatest in Most Deprived Areas
Reductions were greatest in girls whose schools were in the most deprived areas, where children are known to consume the largest amount of sugary drinks. The greatest reductions in obesity were observed in the two most deprived quintiles – such that in the lowest quintile the absolute obesity prevalence reduction was 2.4PP (95% CI 1.6-3.2), equivalent to a 9% reduction in those living in the most deprived areas.
There are several reasons why the sugar tax did not lead to changes in levels of obesity among the younger children, the researchers said. Very young children consume fewer sugar-sweetened drinks than older children, so the soft drinks levy would have had a smaller effect. Also, fruit juices are not included in the levy, but contribute similar amounts of sugar in young children's diets as do sugar-sweetened beverages.
Advertising May Impact Consumption in Boys
It's also unclear why the sugar tax might affect obesity prevalence in girls and boys differently, they said, especially since boys are higher consumers of sugar-sweetened beverages. One explanation is the possible impact of advertising – numerous studies have found that boys are often exposed to more food advertising than girls, both through higher levels of TV viewing and in how adverts are framed. Physical activity is often used to promote junk food and boys, compared with girls, have been shown to be more likely to believe that energy dense junk foods depicted in adverts will boost physical performance, and so are more likely to choose energy-dense, nutrient-poor products following celebrity endorsements.
Tax 'Led to Positive Health impacts'
"Our findings suggest that the UK SDIL led to positive health impacts in the form of reduced obesity levels in girls aged 10-11 years," the authors said. However: "Additional strategies beyond SSB taxation will be needed to reduce obesity prevalence overall, and particularly in older boys and younger children."
Dr Nina Rogers from the MRC Epidemiology Unit at Cambridge, who led the study, said: "We urgently need to find ways to tackle the increasing numbers of children living with obesity, otherwise we risk our children growing up to face significant health problems. That was one reason why the UK's SDIL was introduced, and the evidence so far is promising. We've shown for the first time that it is likely to have helped prevent thousands of children each year becoming obese.
"It isn't a straightforward picture, though, as it was mainly older girls who benefited. But the fact that we saw the biggest difference among girls from areas of high deprivation is important and is a step towards reducing the health inequalities they face."
Although the researchers found an association rather than a causal link, this study adds to previous findings that the levy was associated with a substantial reduction in the amount of sugar in soft drinks.
Senior author Professor Jean Adams from the MRC Epidemiology Unit said: "We know that consuming too many sugary drinks contributes to obesity and that the UK soft drinks levy led to a drop in the amount of sugar in soft drinks available in the UK, so it makes sense that we also see a drop in cases of obesity, although we only found this in girls. Children from more deprived backgrounds tend to consume the largest amount of sugary drinks, and it was among girls in this group that we saw the biggest change."
Tom Sanders, professor emeritus of nutrition and dietetics at King's College London, said: "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."
He added that: "As well as continuing to discourage the consumption of sugar sweetened beverages and sweets, wider recognition should be given to foods such as biscuits [and] deep fried foods (crisps, cornsnacks, chips) that make [a] bigger contribution to excess calorie intake in children. Tackling poverty, however, is probably [the] best way to improve the diets of socially deprived children."
Government 'Should Learn From This Success'
Asked to comment by Medscape News UK,Katharine Jenner, director of the Obesity Health Alliance, said: "Government should be heartened that their soft drinks policy is already improving the health of young girls, regardless of where they live. The Government should learn from this success, especially when compared with the many unsuccessful attempts to persuade industry to change their products voluntarily. They must now press ahead with policies that make it easier for everyone to eat a healthier diet, including extending the soft drinks industry levy to include other less healthy foods and drinks and measures to take junk food out of the spotlight.
"The research notes that numerous studies have found that boys are often exposed to more food advertising content than girls, negating the impact of the soft drinks levy, [so] we need restriction on junk food marketing now, to put healthy food back in the spotlight."
The research was supported by the National Institute of Health and Care Research (NIHR) and the Medical Research Council.