"Children of the 90s are three times as likely to be obese as their parents and grandparents," the Mail Online reports. A UK survey looking at data from 1946 to 2001 found a clear trend of being overweight or obese becoming more widespread in younger generations. Another related trend saw the threshold from being a normal weight to being overweight was passed at a younger age in younger generations
The study examined 273,843 records of weight and height for 56,632 people in the UK from five studies undertaken at different points since 1946. The results found children born in 1991 or 2001 were much more likely to be overweight or obese by the age of 10 than those born before the 1980s, although the average child was still of normal weight.
The study also found successive generations were more likely to be overweight at increasingly younger ages, and the heaviest people in each group got increasingly more obese over time. These results won't come as much of a surprise given the current obesity epidemic.
The findings are a potential public health emergency in the making. Obesity-related complications such as type 2 diabetes, heart disease and stroke can be both debilitating and expensive to treat. The researchers called for urgent effective interventions to buck this trend.
Where did the story come from?
The study was carried out by researchers from University College London and was funded by the Economic and Social Research Council.
The Mail Online focused on the risk to children, saying children were more likely to be obese.
But the figures in the study were for obesity and being overweight combined. We don't know how the chances of obesity alone changed over time because there were too few obese children in the earliest cohorts to carry out the calculations.
BBC News gave a more accurate overview of the study and the statistics.
What kind of research was this?
This was an analysis of data from five large long-running cohort studies carried out in England ranging around 50 years in total. It aimed to see how people's weight changed over time through childhood and adulthood, and how this compared across generations.
Studies like this are useful for looking at patterns and telling us what has changed and how, but can't tell us why these changes arose.
What did the research involve?
Researchers used data from cohort studies that recorded the weight and height of people born in 1946, 1958, 1970, 1991 and 2001.
They used the data to examine how the proportion of people who were normal weight, overweight or obese changed over time for the five birth cohort groups. They also calculated the chances of becoming overweight or obese at different ages, across childhood and adulthood, for the five groups.
The researchers used data from 56,632 people, with 273,843 records of body mass index (BMI) recorded at ages ranging from 2 to 64. BMI is calculated for adults as weight in kilograms divided by height in metres squared.
For children, BMI is assessed differently to account for the way children grow, using a reference population to decide whether children are underweight, normal weight, overweight or obese at specific ages.
To keep the populations as similar as possible across the cohort studies, the researchers only included data on white people, as there were few non-white people in the earliest study. Immigration of non-white people to the UK did not begin in any significant numbers until the 1950s.
For each of the five cohort studies, men were analysed separately from women, and children were analysed separately from adults. Each cohort was divided into 100 equal centiles, or sub-groups, according to BMI – for example, the 50th centile is the group where half the people in the study have a higher BMI and half have a lower BMI.
Tracking the 50th centile over time can show whether the average person in the group is normal weight or overweight at certain ages. Higher centiles, such as the 98th centile, show the BMI of the heaviest people in the group, where only 2% of people in the group had a higher BMI and 97% had a lower BMI.
What were the basic results?
The study found that:
- People born in the more recent birth cohorts were more likely to be overweight at younger ages. The age at which the average (50th centile) subgroup became overweight was 41 for men born in 1946, 33 for men born in 1958, and 30 for men born in 1970. For women, the age fell from 48 to 44, then to 41 across the three birth cohorts.
- The chances of becoming overweight in childhood increased dramatically for children born in 1991 or 2001. For children born in 1946, the chance of being overweight or obese at the age of 10 was 7% for boys and 11% for girls. For children born in 2001, the chance was 23% for boys and 29% for girls. However, the average children (50th centile) remained in the normal weight range in all five birth cohorts.
- The biggest changes in weight were seen at the top end of the spectrum. The heaviest people from the group born in 1970 (98th centile) reached a higher BMI earlier in life than the people born in earlier birth cohorts.
How did the researchers interpret the results?
The researchers say their results show children born after the 1980s are more at risk of being overweight or obese than those born before the 1980s.
They say this is because of their exposure to an "obesogenic environment", with easy access to high-calorie food. They say the changes in obesity over time among older cohorts also support the theory that changes to the food environment in the 1980s are behind the rise in obesity.
They go on to warn that if trends persist, modern day and future generations of children will be more overweight or obese for more of their lives than previous generations, and this could have "severe public health consequences" as they will be more likely to get illnesses such as coronary heart disease and type 2 diabetes.
The study shows how, while the whole population of England has become heavier over the past 70 years, different generations have been affected in different ways. People born in 1946 were, on average, normal weight until their 40s, but this group has since seen their weight rise and they are now, on average, overweight.
By the time they reached 60, 75% of men and 66% of women from this group were overweight or obese. People born in 1946 from the heaviest cohorts, who were already overweight in early adulthood, are now likely to be obese or very obese.
For people born since 1946, the chance of being overweight as young adults, adolescents or children has been increasing. The chances of being overweight or obese by the age of 40 was 65% for men born in 1958 (45% for women) and 67% for men born in 1970 (49% for women). The chances of children born in 2001 being overweight or obese by the age of 10 are almost three times that of the children born in 1946.
We can deduce from the figures that something may have happened during the 1980s – the decade when the earliest birth cohort's average group moved from normal weight to overweight – to increase the chances of people of all ages becoming overweight or obese.
What these figures can't tell us is what that was, despite the researchers' assertion this was a change to an obesogenic environment. Still, it seems plausible that a combination of high-calorie, low-cost food and an increasingly sedentary lifestyle – both in terms of working life and recreation – contributed to this trend.
This study has some limitations. Of the five studies, four were national studies across the UK, while one (the 1991 study) was limited to one area of England, so may not be representative of the UK as a whole.
More importantly, the five studies used differing methods to record height and weight at different time points. Some records were self-reported, which means they rely on people accurately recording and reporting their own height and weight.
We know that being overweight and obese is bad for our health. These conditions increase the chances of a range of illnesses, including heart disease, diabetes and some cancers. We also know children who are overweight tend to grow up to be overweight or obese adults, so increasing their chances of illness.
This study gives us more information about who is at risk of becoming overweight and at which ages, which may help health services develop better strategies for turning the tide of obesity.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Mail Online, 19 May 2015
BBC News, 20 May 2015
Links to the science
PLOS Medicine. Published online May 19 2015