Lifestyle risk behaviours among adolescents: a two-year longitudinal study of the impact of the COVID-19 pandemic

Abstract

Objective

To examine changes in the prevalence of six key chronic disease risk factors (the “Big 6”), from before (2019) to during (2021) the COVID-19 pandemic, among a large and geographically diverse sample of adolescents, and whether differences over time are associated with lockdown status and gender.

Design

Prospective cohort study.

Setting

Three Australian states (New South Wales, Queensland and Western Australia) spanning over 3000 km.

Participants

983 adolescents (baseline M_age=12.6, SD=0.5, 54.8% girl) drawn from the control group of the Health4Life Study.

Primary outcomes

The prevalence of physical inactivity, poor diet (insufficient fruit and vegetable intake, high sugar-sweetened beverage intake, high discretionary food intake), poor sleep, excessive recreational screen time, alcohol use and tobacco use.

Results

The prevalence of excessive recreational screen time (prevalence ratios (PR)=1.06, 95% CI=1.03 to 1.11), insufficient fruit intake (PR=1.50, 95% CI=1.26 to 1.79), and alcohol (PR=4.34, 95% CI=2.82 to 6.67) and tobacco use (PR=4.05 95% CI=1.86 to 8.84) increased over the 2-year period, with alcohol use increasing more among girls (PR=2.34, 95% CI=1.19 to 4.62). The prevalence of insufficient sleep declined across the full sample (PR=0.74, 95% CI=0.68 to 0.81); however, increased among girls (PR=1.24, 95% CI=1.10 to 1.41). The prevalence of high sugar-sweetened beverage (PR=0.61, 95% CI=0.64 to 0.83) and discretionary food consumption (PR=0.73, 95% CI=0.64 to 0.83) reduced among those subjected to stay-at-home orders, compared with those not in lockdown.

Conclusion

Lifestyle risk behaviours, particularly excessive recreational screen time, poor diet, physical inactivity and poor sleep, are prevalent among adolescents. Young people must be supported to find ways to improve or maintain their health, regardless of the course of the pandemic. Targeted approaches to support groups that may be disproportionately impacted, such as adolescent girls, are needed.

Trial registration number

Australian New Zealand Clinical Trials Registry (ACTRN12619000431123)

Correspondence to Dr Lauren Anne Gardner; [email protected]

Strengths and limitations of this study

• A prospective cohort design was used to explore changes in a comprehensive set of health indicators among adolescents, from before (2019) to during (2021) the COVID-19 pandemic, and whether changes varied by gender and lockdown status.

• The study included a large (n=983) and geographically diverse sample of adolescents across three Australian states (New South Wales, Queensland and Western Australia) spanning over 3000 km.

• Limitations of the research include the reliance on self-report measures, and while the sample was diverse, it is not representative of the Australian population.

The global spread of COVID-19 and subsequent lockdown measures have presented challenges worldwide. While disease severity, hospital admissions and deaths have typically been lower among adolescents, compared with adults,¹ government responses, such as movement restrictions and school closures, present further potential health ramifications due to the related changes in lifestyle behaviours. Critically, despite some studies demonstrating the significant physical and mental health consequences of lockdown measures on adolescents,^2–4 research has typically focused on a few select behaviours, rather than a comprehensive set of health indicators. Given the unique presentation of COVID-19 across countries and differing government responses, there is a need to examine health-related changes from a variety of contexts to develop a better understanding of global health.

According to the Oxford COVID-19 Government Response Tracker,⁵ the strictness of lockdown restrictions since the first confirmed cases in January 2020 to October 2021 was similar in Australia, the USA and the UK, with average stringency indexes of 60/100, 59/100 and 61/100, respectively, despite much lower incidence and mortality rates in Australia.⁶ However, there can be substantial variation within countries.^{7 8} In Australia, for example, stringency index values varied between states and territories by as much as 68 during 2020.⁸ The strictest and most extensive lockdown restrictions have been implemented in Victoria and New South Wales (NSW), two of the most populous states that saw heightened case numbers during the January 2020 to October 2021 period, while other Australian states, such as Queensland (QLD) and Western Australia (WA), experienced far fewer cases and restrictions.^{9 10} The Australian context may therefore serve as a case study for understanding the impact of various levels of restrictions on adolescent health behaviours.

Previous research has highlighted the importance of six key lifestyle behaviours, including diet, physical activity, sleep, sedentary behaviour (including recreational screen time), alcohol use and smoking—collectively referred to as the ‘Big 6’—for the short-term and long-term health of adolescents.^11–14 These behaviours are common among youth worldwide, with more than 80% of adolescents insufficiently physically active¹⁵ and screen time rapidly increasing.^{14 16} The Big 6 contribute significantly to global disease burden and are known predictors of chronic diseases, including cancer, cardiovascular disease and mental disorders.^{13 17}

Research suggests that COVID-19 has impacted the Big 6, and in turn, the health of adolescents. For example, youth in Europe and Palestine have gained weight during the pandemic,^{18 19} which may be the result of increased consumption of discretionary food and sugar-sweetened beverages (SSB) during lockdown periods.^{18 20} However, some studies report improvements in dietary behaviours, including less SSB consumption among Colombian adolescents, higher fruit intake among Italian youth and higher vegetable intake among adolescents from Spain, Brazil and Chile.^{20 21} Among the few existing Australian studies, Munasinghe et al ³ found physical distancing measures implemented in the initial lockdown period (March–April 2020) were associated with a decline in fast food consumption among adolescents, but there were no changes in fruit and vegetable consumption. However, it is unknown whether these changes have been sustained, or whether other dietary behaviours changed.

The pandemic presents particular challenges for movement behaviours, including physical activity, sedentary behaviour and sleep. Typically, lockdowns are associated with lower levels of adolescent physical activity^{4 18 20 22 23} and increased screen time, both for remote learning and recreation, resulting in sedentary lifestyles.^{3 4 23 24} However, some research in Australia²⁵ and Germany²⁶ suggests physical activity increased.²⁶ International studies also report an increase in adolescent sleep duration during lockdown periods,^{18 20} but higher prevalence of sleep problems, particularly among girls.²⁷ Similarly, Australian adolescents perceived an increase in sleep difficulties and had increased sleep disturbance during the first lockdown.²⁵ One study²⁸ reported increased sleep duration among Australian adolescents who were engaged in remote learning; however, another³ found no changes.

Studies investigating the impact of the pandemic on adolescent alcohol and tobacco use have produced mixed findings. For example, alcohol use is reported to have increased among Canadian adolescents,²⁹ reduced among Spanish adolescents,³⁰ while there was no change in alcohol or tobacco use among adolescents from the USA.³¹ Further, European research suggests a reduction in adolescent tobacco use during the pandemic period,^{30 32} yet there has been an increase in Uganda.³³ To date, changes in alcohol and tobacco use among Australian adolescents have not been examined.

Evidence suggests that the prevalence of the Big 6 varies by gender. For example, adolescent girls are more likely to be physically inactive, whereas adolescent boys are more likely to engage in high levels of recreational screen time, have a poor diet, and use alcohol and tobacco.^{15 34–38} However, less is known about whether changes in lifestyle behaviours over the pandemic period vary by gender.

To address these gaps in the literature, this study aims to examine changes in the prevalence of the Big 6 among a large, geographically diverse sample of adolescents, from before to during the COVID-19 pandemic, and explore whether differences over time are associated with gender and lockdown status.

Methods

Participants and procedure

The sample comprised participants from three Australian states (NSW, QLD and WA), spanning over 3000 km, who were randomly allocated to the control group of the Health4Life Study.³⁹ Participants who provided written consent and had parental consent (passive, active written or active verbal, depending on approved procedures for the school type and region) completed self-report assessments in a supervised classroom setting. Only students who provided data prior to the beginning of the pandemic (between July and November 2019) and during the pandemic (approximately 24 months after baseline, between July and 10 October 2021) were included in this study. During the 2021 data collection period, Australia had strict border policies, restricting international travel and mandating hotel quarantine, while state-level and territory-level border policies for domestic travel varied.⁴⁰ Greater Sydney, including the Central Coast, Shellharbour and Wollongong were subjected to lockdown restrictions under the NSW stay-at-home Public Health Order⁴¹; the most stringent of which included not being permitted to leave the home unless essential (eg, one person per household to shop for food or 1 hour of exercise per day), movement restricted to a 5 km radius of the home, closure of all non-essential retail (eg, hairdressers), home-based work and schooling requirements, curfews, and mandatory mask wearing, with a high police presence and large fines enforced for non-adherence. QLD, WA and areas outside of Greater Sydney were not subjected to extended stay-at-home lockdown restrictions.

Patient and public involvement

Patients or the public were not involved in the design, or conduct, or reporting, or dissemination plans of our research.

Measures

Sociodemographic characteristics

Participants self-reported their age and gender (male, female, non-binary/gender fluid, missing). A binary ‘lockdown’ variable was created reflecting participants who attended schools in the Greater Sydney region that were subjected to the stay-at-home Public Health Order in 2021 and those who were not.⁴¹

Diet

Dietary intake was assessed using items adapted from the NSW School Physical Activity and Nutrition Survey.⁴² Participants self-reported the number of metric cups of SSB usually consumed per week or day. A binary variable was created to reflect high (≥5–6 cups or more/week) and low consumption (≤4 cups/week). Participants reported how often they consume six discretionary food items (hot chips, French fries, wedges or fried potatoes; potato crisps or other salty snacks; snack foods, for example, sweet and savoury biscuits, cakes, doughnuts or muesli bars; confectionary; ice cream or ice blocks; and takeaway meals or snacks). High discretionary food consumption was defined as eating any of the items ‘2 or more times/day’, or eating at least two of the items ‘3–4 times/week’ or more often. Participants reported the number of serves of fruit and vegetables consumed per day, and in line with the Australian dietary guidelines,⁴³ insufficient fruit and vegetable consumption was defined as <2 serves of fruit and <5 serves of vegetables per day, respectively.

Physical activity

A single item was used to assess the number of days over the past week that participants engaged in moderate-to-vigorous physical activity for at least 60 min.⁴⁴ As per the Australian health guideline, insufficient physical activity was defined as engaging in <60 min of moderate-to-vigorous physical activity/day.⁴⁵

Recreational screen time

The International Sedentary Assessment Tool⁴⁶ was used to evaluate free time spent on a typical weekday and weekend day over the past 7 days watching television/DVDs/streaming services or using an electronic device. In line with the Australian health guideline,⁴⁵ excessive recreational screen time was defined as >2 hours/day.

Sleep

The Modified Sleep Habits Survey⁴⁷ was used to assess sleep duration. Total sleep time was calculated by finding the difference between the time participants reported first attempting sleep, and the time they woke up in the morning, minus the reported time taken to fall asleep from first attempt, with a weighted average sleep duration calculated for school and weekend nights. Self-reported bedtime, waketime and sleep duration have been shown to be reliable and valid in adolescent populations.^{48 49} As per the Australian guidelines, insufficient sleep was defined as an average duration outside of 9–11 hours/night for those aged 11–13 years, or 8–10 hours/night for those aged 14–17 years.⁴⁵

Alcohol and tobacco use

Alcohol and tobacco use were measured using two dichotomous (yes/no) items drawn from previous large scale trials and population based epidemiological surveys^{50 51}: ‘Have you had a full standard alcoholic drink in the past 6 months?’ and ‘In the past 6 months, have you tried cigarette smoking, even one or two puffs?’

Statistical analysis

Generalised linear mixed models were used to investigate change over time in the Big 6. Owing to the high prevalence of outcomes, we used Robust Poisson methods to generate prevalence ratios (PR) and 95% CIs, to overcome some of the limitations of reporting ORs from logistic regressions, which may appear inflated.⁵² PR are interpreted as the estimated prevalence of an outcome in one group, compared with another, providing an indication of a change in prevalence, as opposed to risk or odds. All models included a random intercept at the student level and school level, Robust Poisson distribution and a log link function, where time is continuous and represents the prepandemic (2019) and mid-pandemic scores (2021). Group by time interactions were estimated to assess change in the prevalence of the Big 6 over time in relation to gender (female/male, given the low prevalence of the ‘non-binary/gender fluid’ (0.1%) and ‘prefer not to say’ (.5%) subgroups) and the presence of lockdown restrictions during the 2021 survey occasion. All analyses were conducted in Stata V.17.⁵³

Results

Descriptive statistics

The sample included 983 students (baseline M_age=12.6, SD=0.5, 54.8% girl) from 22 schools across NSW, QLD and WA (see table 1 for baseline characteristics). At the 2021 survey occasion, approximately one-third of the sample (32.7%) was under lockdown restrictions. Table 2 presents the prevalence of lifestyle risk behaviours over time.

Table 1

Sample characteristics

Characteristic	n (%)
Gender (n=976)
Female	535 (54.8)
Male	441 (45.2)
State (n=983)
New South Wales	451 (45.9)
Queensland	214 (21.8)
Western Australia	318 (32.3)
School type (n=22)
Independent	14 (63.6)
Catholic	2 (9.1)
Government	6 (27.3)
Country of birth (n=982)
Australia	842 (85.7)
Other	140 (14.3)

Table 2

Prevalence of lifestyle risk behaviours before and during the COVID-19 pandemic

Risk behaviour	Prepandemic (2019), n (%)	During the pandemic (2021), n (%)
High SSB consumption (≥5 cups/week)	90/964 (9.3)	72/935 (7.7)
High discretionary food intake (≥1 item ≥2 times/day or ≥2 items ≥3–4 times/week)	347/813 (42.7)	360/870 (41.4)
Insufficient fruit intake (<2 serves/day)	190/960 (19.8)	279/936 (29.8)
Insufficient vegetable intake (<5 serves/day)	792/958 (82.7)	783/936 (83.7)
Insufficient sleep (outside recommended guidelines*)	549/917 (59.9)	392/885 (44.3)
Excessive recreational screen time (>2 hours/day)	825/964 (85.6)	878/925 (93.8)
Insufficient physical activity (<60 min MVPA/day)	757/949 (79.8)	764/931 (82.1)
Alcohol use (full standard drink in past 6 months)	21/940 (2.2)	91/928 (9.8)
Tobacco use (any use in past 6 months)	8/936 (0.9)	32/924 (3.5)

*≤13 years old: 9–11 hours/night, 14–17 years: 8–10 hours/night.

MVPA, moderate-to-vigorous physical activity; SSB, sugar-sweetened beverage.

Changes in lifestyle risk behaviours

Change over time in the prevalence of the Big 6 and differences based on lockdown status and gender are illustrated in figure 1, with PR and CIs detailed in online supplemental table 1.

Figure 1. Change over time in the prevalence of the Big 6 and differences based on lockdown status and gender. a <=13 years old: 9 to 11 hours/night, 14-17years: 8 to 10 hours/night. MVPA, moderate-to-vigorous physical activity; SSB, sugar-sweetened beverage.

Dietary behaviours

SSB consumption

There was no significant change in the prevalence of high SSB consumption over time (PR=0.83 95% CI=0.58 to 1.18). However, the prevalence was 39% lower in individuals under lockdown (PR=0.61, 95% CI=0.64 to 0.83) over time, compared with those not in lockdown.

Discretionary food consumption

There was no significant change in the prevalence of high discretionary food consumption over time (PR=0.97, 95% CI=0.86 to 1.09). However, the prevalence was 27% lower for individuals living under lockdown (PR=0.73, 95% CI=0.64 to 0.83) over time, compared with those not in lockdown.

Fruit and vegetable intake

The prevalence of insufficient fruit intake increased by 50% over time (PR=1.50, 95% CI=1.26 to 1.79). There were no changes in the prevalence of insufficient vegetable intake over time (PR=1.01, 95% CI=0.97 to 1.06), and the presence of lockdown restrictions was not associated with a change in the prevalence of insufficient fruit or vegetable intake over time.

There were no gender-based differences in the prevalence of high SSB consumption, high discretionary food consumption or insufficient fruit/vegetable intake over time.

Sleep

The prevalence of insufficient sleep decreased by 26% over time (PR=0.74 95% CI=0.68 to 0.81). Girls reported a higher prevalence of insufficient sleep over time, compared with boys (PR=1.24, 95% CI=1.10 to 1.41). The presence of lockdown restrictions was not associated with a change in the prevalence of insufficient sleep over time.

Recreational screen time

There was a 6% increase in the prevalence of excessive recreational screen time over time (PR=1.06, 95% CI=1.03 to 1.11). Gender and the presence of lockdown restrictions were not associated with a change in the prevalence of excessive recreational screen time over time.

Physical activity

There was no change in the prevalence of insufficient physical activity over time (PR=1.03, 95% CI=1.00 to 1.07). Neither gender nor the presence of lockdown restrictions was associated with change in the prevalence of insufficient physical activity over time.

Alcohol use

The prevalence of past 6-month alcohol use increased by 334% over time (PR=4.34, 95% CI=2.82 to 6.67). The prevalence of alcohol use increased more in girls compared with boys (PR=2.34, 95% CI=1.19 to 4.62). The presence of lockdown restrictions was not associated with change in the prevalence of past 6-month alcohol use over time.

Tobacco use

The prevalence of past 6-month tobacco use increased by 305% over time (PR=4.05 95% CI=1.86 to 8.84). Neither gender nor the presence of lockdown restrictions was associated with change in the prevalence of past 6-month tobacco use over time.

Discussion

This study was the first to explore changes in all of the Big 6 lifestyle risk behaviours among a large, geographically diverse cohort of adolescents, from before (2019) to during (2021) the COVID-19 pandemic, and whether changes varied by gender and lockdown status. Over the 2-year period, the prevalence of excessive recreational screen time, insufficient fruit intake and alcohol and tobacco use increased, with alcohol use increasing among girls in particular. The prevalence of insufficient sleep reduced in the overall sample; yet, increased among girls. Being in lockdown was associated with improvements in SSB consumption and discretionary food intake.

These findings highlight the varied impact of the pandemic across countries. For example, consistent with other Australian findings,³ but in contrast to international research,^{18 20} the prevalence of discretionary food intake decreased among those in lockdown. Yet in line with some international findings,²¹ SSB intake reduced among adolescents in lockdown. This may reflect increased parental monitoring during lockdown and reduced opportunistic exposure to fast food due to not being with friends or commuting to school.^{54 55} As such, continued parental monitoring beyond the lockdown period and the promotion of healthy food options may be beneficial. However, improvements in healthy dietary behaviours were not observed. In fact, the prevalence of insufficient fruit intake increased among the full sample. This may relate to the higher cost of fresh fruit and vegetables in Australia during the pandemic, caused by labour shortages within the farming, wholesale and retail sectors due to fewer working holiday-makers.⁵⁶ These findings support calls for governments to consider broader policy-level changes to improve diet, such as taxes and subsidies.⁵⁷

The finding that sleep duration improved from before to during the pandemic is consistent with some Australian²⁸ and international^{18 20} studies. This contrasts typical trends over adolescence^{58 59} and was despite an increase in the prevalence of excessive recreational screen time, which is often considered a primary contributor to poor sleep.⁶⁰ It is posited that the time usually spent getting ready and commuting to school is instead spent getting additional sleep during periods of lockdown, leading to calls for delayed school start times²⁸; however, we found no differences based on lockdown status to support this. The finding that insufficient sleep increased among girls is consistent with international research reporting increased sleep disorders among girls during the pandemic²⁷ and may reflect the association between girl pubertal maturation and the emergence of insomnia symptoms.⁶¹ Targeted intervention approaches to address sleep among girls are needed.

Notably, in contrast to previous international and Australian research attributing increased screen time to lockdown and physical distancing measures,^{3 4 23} we found no difference in the prevalence of excessive recreational screen time between the lockdown and non-lockdown groups. This increase may instead reflect general trends of increasing screen time among adolescents.¹⁶ These findings highlight the value of assessing behaviours among adolescents both in lockdown and not in lockdown in the same period for comparability, and the need for effective interventions targeting screen time among adolescents.³⁹

Contrasting typical trends over adolescence and previous pandemic research,^{4 23} the prevalence of insufficient physical activity did not change over time, nor did it increase more for those in lockdown. Previous studies have attributed reductions in physical activity during the pandemic to government responses, such as the cancellation of organised sport and closure of gyms and recreation centres.^{1 23} However, given the current data were from the 2021 lockdown, whereas previous studies focused on the initial lockdown in 2020, it may be that over time, adolescents have learnt to adapt to the rapidly changing situation and find other ways to achieve their physical activity goals (eg, replaced organised sport with outdoor gym sessions and training). It may also be that other forms of physical activity, such as light and incidental physical activity, have been more severely impacted. Future research would benefit from assessing how these different forms of physical activities changed throughout the pandemic.

Finally, although alcohol and tobacco use increased over time, the prevalence of these behaviours at the first timepoint, when participants were aged 12, was very low and remained relatively low 24 months later. This increase is to be expected among adolescents⁶²; however, the greater increase in alcohol use among girls was unexpected. Considering this and the increase in prevalence of insufficient sleep, girls may be disproportionately impacted by the pandemic. This may reflect general patterns of higher prevalence and increasing trends of mental health problems among adolescent girls across the globe,^{63 64} which are often comorbid with poor sleep and substance use; as well as narrowing of the gender gap in alcohol use among more among recent cohorts.^{35 65} Links between these factors are complex⁶⁶ and assessing changes in mental health alongside changes in the Big 6 may be a useful future research direction.

Key strengths of this study include having assessment occasions before and during the pandemic, rather than relying on retrospective accounts of perceived changes in behaviours, and a sample comprised of adolescents both in and not in lockdown at follow-up for comparability. However, we cannot rule out the potential impact of other factors, such as maturation or mental health, that could also be influencing the Big 6. Although the study builds on previous research that has focused on the early pandemic period, claims about behavioural shifts across the early and late pandemic periods need to be interpreted with caution. Other limitations include the reliance on self-report measures, and while the sample was more diverse than other Australian studies, it is limited to three Australian states and is therefore not representative of the entire Australian adolescent population.¹⁴

Conclusion

Lifestyle risk behaviours, particularly excessive recreational screen time, poor diet, physical inactivity and poor sleep, are prevalent among adolescents and should be addressed with effective behaviour change interventions.³⁹ With the pandemic remaining a continually evolving situation across the world, the impact on health behaviours is also likely to be dynamic and diverse. Supporting young people to improve or maintain their health behaviours, regardless of the course of the pandemic, is important, alongside targeted research and intervention efforts to support groups that may be disproportionately impacted, such as adolescent girls.

The Health4Life Study was led by researchers at the Matilda Centre at the University of Sydney, Curtin University, the University of Queensland, the University of Newcastle, Northwestern University, and UNSW Sydney: MT, NN, F.J. Kay-Lambkin, KC, CC, L.K. Thornton, T. Slade, K.L. Mills, M. Sunderland, J.D. Bauer, B.J. Parmenter, B. Spring, D.R. Lubans, S.J. Allsop, L. Hides, N.T. McBride, E.L. Barrett, L.A. Stapinski, L. Mewton, L.E. Birrell, C. Quinn and LAG. The authors would like to acknowledge all the research staff who have worked across the study, as well as the schools, students and teachers who participated in this research. The research team also acknowledges the assistance of the New South Wales Department of Education (SERAP 2019006), the Catholic Education Diocese of Bathurst, the Catholic Schools Office Diocese of Maitland-Newcastle, Edmund Rice Education Australia, the Brisbane Catholic Education Committee (373), and Catholic Education Western Australia (RP2019/07) for access to their schools to conduct this research.

Data availability statement

Data are available upon reasonable request.

Ethics statements

Patient consent for publication

Not applicable.

Ethics approval

This study involves human participants. Ethical approval was gained from the University of Sydney (2018/882), NSW Department of Education (SERAP No. 2019006), University of Queensland (2019000037), Curtin University (HRE2019-0083) and relevant Catholic school committees. Participants gave informed consent to participate in the study before taking part.

Footnote

Twitter @jennidebenham, @NickieNewton, @BridieOsman

Contributors LAG conceptualised the study, with assistance from KEC and NCN. Acquisition of the data was contributed to by LAG, KEC, BO, NCN, MT and CC. Analysis and interpretation of data was led by JD and LAG. LAG led the write up of the manuscript with assistance from JD, FEW and BO. All authors critically revised and approved the final manuscript. LAG is responsible for the overall content as guarantor.

Funding The Health4Life Study was funded by the Paul Ramsay Foundation and the Australian National Health and Medical Research Council via Fellowships (KC, APP1120641; MT, APP1078407; and NN, APP1166377) and via a Centre of Research Excellence in the Prevention and Early Intervention in Mental Illness and Substance Use (PREMISE; APP11349009).

Competing interests None declared.

Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

Provenance and peer review Not commissioned; externally peer reviewed.

Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

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