Large-scale study suggests under 45s and women more likely to gain weight and jump a BMI category during COVID-19 lockdown

A large-scale study of almost a million UK adults led by Leicester researchers has revealed that under 45s and women were more likely to gain weight and jump a body mass index (BMI) category during COVID-19 lockdown.

The findings were presented for the first time on Thursday at the European Congress on Obesity (ECO) in Maastricht, Netherlands by co-author Tom Yates, Professor of Physical Activity, Sedentary Behaviour and Health at the University of Leicester and part of the National Institute for Health and Care Research (NIHR) Leicester Biomedical Research Centre. Professor Yates said: “The implications of even modest weight gain at a population level in younger adults and women could translate into more diabetes, heart disease, cancers and other serious obesity-related health problems over the coming decades in these populations unless action is taken to reverse the effects of lockdown.

“These data also suggest societal inequalities, with Black individuals more likely to put on pandemic weight and move up at least one BMI category compared to other ethnic groups.”

Lead author Dr David Kloecker, of the Leicester Real World Evidence Unit, Leicester Diabetes Centre, added: “Prolonged periods of lockdown disrupted daily routines making it challenging for people to eat healthily and keep fit, with emotional eating and sports club closures likely intensifying the trend.

“Nevertheless, more research is needed to understand the reasons behind these changes in bodyweight and obesity levels.”

Even before the COVID-19 pandemic, obesity was one of the UK’s most pressing public health challenges. According to the Health Survey for England, around three-quarters of those aged 45 to 74 years were living with overweight or obesity in 2019.

For this study, researchers conducted a retrospective observational cohort study of almost one million adults (aged 18 or older), randomly selected from the Clinical Practice Research Datalink (CPRD – a large general practice database) to investigate how BMI and weight changed after the first COVID-19 lockdown in the UK, and whether these changes differed by BMI category, sex, age group and ethnicity.

The pre-lockdown period spanned March 22, 2017 to March 22, 2020 (the day before the start of the first lockdown in the UK), and the follow-up lockdown period was from March 23, 2020 to March 13, 2021.

In total, 938,150 adults were included in the first analysis comparing body weight trajectories after the lockdown with historical trends. Participants were divided into five groups based on their first recorded BMI measurement prior to lockdown. 32% were classed as ‘underweight’ or ‘healthy weight’, 35% ‘overweight’ and 33% with obesity (either class 1, 2 or 3).

Analyses were then broken down by demographic characteristics: sex (male and female), age (under 45 years old, 45 years to <60 years, 60 to <75 years, and 75 years and older), and ethnicity (White, South Asian, Black, and Mixed/Other). The majority (58%) were female and White (83%), with an average (median) age of 55 years.

The researchers found small changes in body weight trends after the start of lockdown in women and those younger than 45 years old with a BMI of ≥ 30 kg/m2 relative to historical trends.

Further analyses of data from 273,529 participants (with information on BMI before and after the start of the first UK lockdown) looking at changes in BMI, found that most adults remained in the same BMI category post-lockdown.

In those who started off at a healthy weight before the pandemic, 83% remained in the same BMI category post-lockdown, 14% became overweight or obese, and around 3% transitioned into the underweight category.

Similar proportions of adults living with overweight prior to lockdown experienced weight gain (11%) and weight loss (12%) that led to changes in BMI category post-lockdown. Among adults living with any class of obesity before the first lockdown, around 1 in 10 lost enough weight to transition into the overweight, normal weight or underweight categories.

The researchers also found that a greater proportion of women than men gained weight, resulting in an increase in BMI category post-lockdown. For example, in the overweight category, 13% of women versus 9% of men transitioned into the obesity categories (any class) post-lockdown.

Similarly, compared with older age groups, those aged younger than 45 years were more likely to gain weight and move up at least one BMI category post-lockdown. For example, in the overweight category 17% (over 1 in 6) moved into the obesity categories.

‘Body mass index change during the COVID-19 pandemic: A UK retrospective cohort study in one million individuals’ was first presented as poster PO2.36 at the European Congress on Obesity. This study was sponsored by global healthcare company Novo Nordisk.

The research is supported by the NIHR Leicester Biomedical Research Centre and NIHR Applied Research Collaboration East Midlands.