Population-level trends in the distribution of body mass index in England, 1992-2013

Trends in the ability of socioeconomic position to predict individual body mass index: an analysis of repeated cross-sectional data, 1991-2019

BACKGROUND

The widening of group-level socioeconomic differences in body mass index (BMI) has received considerable research attention. However, the predictive power of socioeconomic position (SEP) indicators at the individual level remains uncertain, as does the potential temporal variation in their predictive value. Examining this is important given the increasing incorporation of SEP indicators into predictive algorithms and calls to reduce social inequality to tackle the obesity epidemic. We thus investigated SEP differences in BMI over three decades of the obesity epidemic in England, comparing population-wide (SEP group differences in mean BMI) and individual-level (out-of-sample prediction of individuals' BMI) approaches to understanding social inequalities.

METHODS

We used repeated cross-sectional data from the Health Survey for England, 1991-2019. BMI (kg/m2) was measured objectively, and SEP was measured via educational attainment, occupational class, and neighbourhood index of deprivation. We ran random forest models for each survey year and measure of SEP adjusting for age and sex.

RESULTS

The mean and variance of BMI increased within each SEP group over the study period. Mean differences in BMI by SEP group also increased: differences between lowest and highest education groups were 1.0 kg/m2 (0.4, 1.6) in 1991 and 1.3 kg/m2 (0.7, 1.8) in 2019. At the individual level, the predictive capacity of SEP was low, though increased in later years: including education in models improved predictive accuracy (mean absolute error) by 0.14% (- 0.9, 1.08) in 1991 and 1.05% (0.18, 1.82) in 2019. Similar patterns were obtained for occupational class and neighbourhood deprivation and when analysing obesity as an outcome.

CONCLUSIONS

SEP has become increasingly important at the population (group difference) and individual (prediction) levels. However, predictive ability remains low, suggesting limited utility of including SEP in prediction algorithms. Assuming links are causal, abolishing SEP differences in BMI could have a large effect on population health but would neither reverse the obesity epidemic nor reduce much of the variation in BMI.

Challenges in obtaining accurate anthropometric measures for adults with severe obesity: A community-based study

AIMS

The number of people with severe obesity (BMI ⩾40 kg/m²) is increasing rapidly, but is poorly documented, partly as a result of inappropriate standard anthropometric measurement methods for community-based people.

METHODS

As part of a broader study, people receiving care services and with severe obesity were visited at home. The people were assessed for measurements using different weighing scales and a standard portable stadiometer. If the stadiometer could not be used, their half arm span and knee height were measured to estimate their height using standard predictive equations.

RESULTS

Measurements were taken for 15 women and 10 men (n = 25) aged 40-87 years (mean 62 years). Weights ranged from 98.4 to 211.8 kg (mean 150 kg), with 16 participants requiring bariatric scales. For the six people who were unable to stand, we used wheelchair scales (n = 1), bed weighing scales (n = 2), routine weights from care home records (n = 2) or weight data from hospital records (n = 1). The standard portable stadiometer could only be used for one person; the others required alternative measures from which to estimate height. Large body habitus obscured bony landmarks, meaning alternative measures gave diverse heights. Fourteen participants had a ⩾8 cm difference in height between estimates from half arm span and knee height measurements.

CONCLUSIONS

Standard practice commonly does not provide reliable measurements for people with severe obesity, particularly those with mobility difficulties. An inability to measure weight and height accurately can exclude people from appropriate care, obscuring the true numbers affected and the effectiveness of future service planning. Safe community care requires the availability of specialist scales and standardised methods for height estimation appropriate for older and disabled people with severe obesity.

Trends in cardiovascular disease risk factors by BMI category among adults in England, 2003-2018

OBJECTIVE

This study aimed to estimate trends in cardiovascular disease risk factors by BMI category among adults in England (n = 115,860).

METHODS

Risk factors included cigarette smoking, hypertension, total diabetes, and raised total cholesterol. Risk factor prevalence was computed in the following four 4-year time periods: 2003-2006; 2007-2010; 2011-2014; and 2015-2018. Change was computed as the difference between the first and last time periods, expressed in percentage points (PP).

RESULTS

Hypertension remained at a stable level among men with normal weight but decreased among men with obesity (-4.1 PP; 95% CI: -7.1 to -1.0). Total diabetes remained at a stable level among adults with normal weight but increased among adults with obesity (men: 3.5 PP, 95% CI: 1.2 to 5.7; women: 3.6 PP, 95% CI: 1.8 to 5.4). Raised total cholesterol decreased in all BMI groups but fell more sharply among women with obesity (-21 PP; 95% CI: -25 to -17) versus their counterparts with normal weight (-16 PP; 95% CI: -18 to -14).

CONCLUSIONS

Greater reductions in hypertension and raised total cholesterol among adults with overweight and obesity partially reflect improvements in screening, treatment, and control among those at highest cardiovascular risk. Higher levels of risk factor prevalence among adults with overweight and obesity, in parallel with rising diabetes, highlight the importance of national prevention efforts to combat the public health impact of excess adiposity.

Heterogeneous contributions of change in population distribution of body mass index to change in obesity and underweight

From 1985 to 2016, the prevalence of underweight decreased, and that of obesity and severe obesity increased, in most regions, with significant variation in the magnitude of these changes across regions. We investigated how much change in mean body mass index (BMI) explains changes in the prevalence of underweight, obesity, and severe obesity in different regions using data from 2896 population-based studies with 187 million participants. Changes in the prevalence of underweight and total obesity, and to a lesser extent severe obesity, are largely driven by shifts in the distribution of BMI, with smaller contributions from changes in the shape of the distribution. In East and Southeast Asia and sub-Saharan Africa, the underweight tail of the BMI distribution was left behind as the distribution shifted. There is a need for policies that address all forms of malnutrition by making healthy foods accessible and affordable, while restricting unhealthy foods through fiscal and regulatory restrictions.

Biomarkers, disability and health care demand

Using longitudinal data from a representative UK panel, we focus on a group of apparently healthy individuals with no history of disability or major chronic health condition at baseline. A latent variable structural equation model is used to analyse the predictive role of latent baseline biological health, indicated by a rich set of biomarkers, and other personal characteristics, in determining the individual's disability state and health service utilisation five years later. We find that baseline biological health affects future health service utilisation very strongly, via progression to functional disability channel. We also find systematic income gradients in future disability risks, with those of higher income experiencing a lower progress to disability. Our model reveals that observed pro-rich inequity in health care utilisation, is driven by the fact that higher-income people tend to make greater use of health care treatment, for any given biological health and disability status; this is despite the lower average need for treatment shown by the negative association of income with both baseline ill biological health and disability progression risk. Factor loadings for latent baseline health show that a broader set of blood-based biomarkers, rather than the current focus mainly on blood pressure, cholesterol and adiposity, may need to be considered for public health screening programs.

Flexible age-period-cohort modelling illustrated using obesity prevalence data

Background

Use of generalized linear models with continuous, non-linear functions for age, period and cohort makes it possible to estimate these effects so they are interpretable, reliable and easily displayed graphically. To demonstrate the methods we use data on the prevalence of obesity among Australian women from two independent data sources obtained using different study designs.

Methods

We used data from two long-running nationally representative studies: seven cross-sectional Australian National Health Surveys conducted between 1995 and 2017–18, each involving 6000–8000 women; and the Australian Longitudinal Study on Women’s Health which started in 1996 and involves more than 57,000 women in four age cohorts who are re-surveyed at three-yearly intervals or annually. Age-period-cohort analysis was conducted using generalized linear models with splines to describe non-linear continuous effects.

Results

When analysed in the same way both data sets showed similar patterns. Prevalence of obesity increased with age until late middle age and then declined; increased only slightly across surveys; but increased steadily with birth year until the 1960s and then accelerated.

Conclusions

The methods illustrated here make the estimation and visualisation of age, period and cohort effects accessible and interpretable. Regardless of how the data are collected (from repeated cross-sectional surveys or longitudinal cohort studies), it is clear that younger generations of Australian women are becoming heavier at younger ages. Analyses of trends in obesity should include cohort, in addition to age and period, effects in order to focus preventive strategies appropriately.

Change in the distribution of body mass index in Brazil: analysing the interindividual inequality between 1974 and 2013

BACKGROUND

Brazil is among the 10 countries with the highest prevalence of overweight in the world. The aim was to analyse the changes in the dispersion of body mass index (BMI) in the Brazilian population from the 1970s to 2013 in specific population groups.

METHODS

Data were extracted from five national household surveys between 1974-1975 and 2013, including adults aged 20 to 64. We calculated SD, median, fifth and 95th percentiles of BMI for each sociodemographic category (sex, age, schooling) and survey year in order to explore whether changes in mean BMI are followed by changes in dispersion.

RESULTS

During the period the mean BMI ranged from 22.7 kg/m² to 26.6 kg/m², with a much higher variation in the 95th percentile (+6.1 kg/m²) when compared with the fifth percentile (+1.8 kg/m²). The within-group differences increased over time. The SD increased in all categories analysed and was higher among women, lower schooling groups and the oldest group. An increase of 1.0 kg/m² in the BMI mean was associated with an increase of 0.32 kg/m² in the SD, 0.45 kg/m² in the fifth percentile and 1.50 kg/m² in the 95th percentile of BMI.

CONCLUSIONS

Population changes occurred in BMI are more complex than the simple increase of its average. Concomitant to the increase in BMI, there was an increase in the within-group differences, showing that growing inequalities are not driven solely by sociodemographic factors.

Association between population mean and distribution of deviance in demographic surveys from 65 countries: cross sectional study

OBJECTIVES

To examine whether conditions related to scarcity at the left side of the distribution (anaemia, severe chronic energy deficiency, and underweight) are as strongly related to population means as conditions of excess at the right side of the distribution (overweight and obesity).

DESIGN

Observational study.

SETTING

65 countries, with nationally representative cross sectional data from 1994 to 2014 obtained from the Demographic Health Surveys.

PARTICIPANTS

Non-pregnant women aged 20-49. Sample of 65 countries and n=524 380 for analysis of BMI; sample of 44 countries and n=316 465 for analysis of haemoglobin.

MAIN OUTCOME MEASURES

The association between mean and prevalence of each category. For BMI, prevalence of severe chronic energy deficiency (SCED, BMI <16.0), underweight (BMI <18.5), overweight (BMI >25) and obese (BMI >30.) were measured; for haemoglobin, prevalence of anaemia (haemoglobin <12.0 g/dL) and severe anaemia (haemoglobin <8.0 g/dL) were examined.

RESULTS

There was a strong association between mean BMI and prevalence of overweight (r²=0.98; r=0.99; β=8.3 (8.0 to 8.6)) and obesity (r²=0.93; r=0.97; β=4.2 (3.9 to 4.5)). For left sided conditions, a moderate to strong association was found between mean BMI and prevalence of underweight (r²=0.67; r=-0.82; β=-2.7 (-3.1 to -2.2)), and a weaker association for SCED (r²=0.38; r=-0.61; β=-0.32 (-0.43 to -0.22)). There was a moderate association between mean haemoglobin and prevalence of anaemia (r²=0.46; r=-0.68; β=-10.8 (-14.5 to -7.1)) and a weaker association with severe anaemia (r²=0.30; r=-0.55; β=-0.55 (-0.81 to -0.29)).

CONCLUSIONS

The associations between population means and prevalence of conditions of scarcity such as low BMI and anaemia were substantially weaker than the associations of mean BMI with conditions of excesses such as overweight and obesity.

Population-level trends in the distribution of body mass index in Canada, 2000-2014

OBJECTIVE

Research studying population-level body mass index (BMI) trends document increases in mean or prevalence of overweight/obese but less consideration has been given to describing the changing distribution of BMI. The objective of this research was to perform a detailed analysis of changes in the BMI distribution in Canada.

METHODS

Using data from the CCHS (2000-2014), we analyzed distributional parameters of BMI for 492,886 adults aged 25-64 years. We further stratified these analyses for women and men, education level, and region of residence.

RESULTS

Mean BMI has increased for most subgroups of the Canadian population. Mean BMI values were higher for men, while standard deviation (SD) of the BMI distribution was systematically higher in women. Increases in mean BMI were accompanied with increases in SD of BMI across cycles. Across survey cycles, the 95th percentile increased more than 10 times more rapidly compared to the 5th percentile, showing a very unequal change between extreme values in the BMI distribution over time. There was a relationship between SD with BMI, but these relations were generally not different between educational categories and regions. This suggests that the growing inter-individual inequalities (i.e., dispersion) in BMI were not solely attributable to socioeconomic and demographic factors.

CONCLUSIONS

This study supports the hypothesis that the simultaneous increases in mean BMI and SD of the BMI distribution are occurring, and suggests the need to move beyond the mean-centric paradigm when studying a complex public health phenomenon such as population change in BMI.

Neighbourhood typologies and associations with body mass index and obesity: A cross-sectional study

Little research has investigated associations between a combined measure of the food and physical activity (PA) environment, BMI (body-mass-index) and obesity. Cross-sectional data (n=22,889, age 18-86years) from the Yorkshire Health Study were used [2010-2013]. BMI was calculated using self-reported height and weight; obesity=BMI≥30. Neighbourhood was defined as a 2km radial buffer. Food outlets and PA facilities were sourced from Ordnance Survey Points of Interest (PoI) and categorised into 'fast-food', 'large supermarkets', 'convenience and other food retail outlets' and 'physical activity facilities'. Parks were sourced from Open Street Map. Latent class analysis was conducted on these five environmental variables and availability was defined by quartiles of exposure. Linear and logistic regressions were then conducted for BMI and obesity respectively for different neighbourhood types. Models adjusted for age, gender, ethnicity, area-level deprivation, and rural/urban classification. A five-class solution demonstrated best fit and was interpretable. Neighbourhood typologies were defined as; 'low availability', 'moderate availability', 'moderate PA, limited food', 'saturated' and 'moderate PA, ample food'. Compared to low availability, one typology demonstrated lower BMI (saturated, b=-0.50, [95% CI=-0.76, -0.23]), while three showed higher BMI (moderate availability, b=0.49 [0.27, 0.72]; moderate PA, limited food, b=0.30 [0.01, 0.59]; moderate PA, ample food, b=0.32 [0.08, 0.57]). Furthermore, compared to the low availability, saturated neighbourhoods showed lower odds of obesity (OR=0.86 [0.75, 0.99]) while moderate availability showed greater odds of obesity (OR=1.18 [1.05, 1.32]). This study supports population-level approaches to tackling obesity however neighbourhoods contained features that were health-promoting and -constraining.

Trends in the distribution of body mass index and waist circumference among South Korean adults, 1998-2014

BACKGROUND/OBJECTIVES

An increase in mean body mass index (BMI) or prevalence of obesity may be accompanied by changes in the population BMI distribution. This study aimed to examine how the distributions of BMI and waist circumference (WC) have changed in South Korea over a 16-year interval (1998-2014).

SUBJECTS/METHODS

Using the Korea National Health and Nutrition Examination Survey, we analyzed changes in mean, standard deviation (SD), 5th, and 95th percentile values of BMI and WC distributions for 46,343 (BMI) and 46,327 (WC) adults aged 25-64 years.

RESULTS

For men, mean BMI increased at an annual rate of 0.060 units (95% CI: 0.047-0.073) with annual increases of 0.029 units in SD (95% CI: 0.019-0.039), 0.121 units in the 95th percentile (95% CI: 0.097-0.145) and 0.042 units in the 5th percentile (95% CI: 0.021-0.062). The 95th percentile and SD of the WC distribution increased, but not mean WC and the 5th percentile. For women, mean BMI decreased at an annual rate of 0.030 units (95% CI: 0.010-0.049) with a 0.030-unit increase in SD (95% CI: 0.012-0.048) and a 0.049-unit decrease in the 5th percentile (95% CI: 0.029-0.070). Mean WC also decreased with an increase in SD and a decrease in the 5th percentile.

CONCLUSIONS

These findings suggest increasing dispersion in the distribution of BMI and WC derived from significant shifts in the upper tails for Korean men, but not women. Future research needs to identify the factors that underlie the increasing dispersion of obesity measures.

Influence of social deprivation on provision of bariatric surgery: 10-year comparative ecological study between two UK specialist centres

OBJECTIVE

To investigate the effect of residential location and socioeconomic deprivation on the provision of bariatric surgery.

DESIGN

Retrospective cross-sectional ecological study.

SETTING

Patients resident local to one of two specialist bariatric units, in different regions of the UK, who received obesity surgery between 2003 and 2013.

METHODS

Demographic data were collected from prospectively collected databases. Index of Multiple Deprivation (IMD 2010) was used as a measure of socioeconomic status. Obesity prevalences were obtained from Public Health England (2006). Patients were split into three IMD tertiles (high, median, low) and also tertiles of time. A generalised linear model was generated for each time period to investigate the effect of socioeconomic deprivation on the relationship between bariatric case count and prevalence of obesity. We used these to estimate surgical intervention provided in each population in each period at differing levels of deprivation.

RESULTS

Data were included from 1163 bariatric cases (centre 1-414, centre 2-749). Incidence rate ratios (IRRs) were calculated to measure the associations between predictor and response variables. Associations were highly non-linear and changed over the 10-year study period. In general, the relationship between surgical case volume and obesity prevalence has weakened over time, with high volumes becoming less associated with prevalence of obesity.

DISCUSSION

As bariatric services have matured, the associations between demand and supply factors have changed. Socioeconomic deprivation is not apparently a barrier to service provision more recently, but the positive relationships between obesity and surgical volume we would expect to find are absent. This suggests that interventions are not being taken up in the areas of need. We recommend a more detailed national analysis of the relationship between supply side and demand side factors in the provision of bariatric surgery.

Access and quality of parks and associations with obesity: A cross-sectional study

Public health is increasingly engaging with multi-faceted obesity prevention efforts. Although parks represent key community assets for broader public health, they may not be distributed equitably and associations with obesity are equivocal. We investigated park access and quality relative to deprivation and obesity with individual-level data from the Yorkshire Health Study. Compared to the least deprived areas, the moderately and most deprived areas had a greater park access and park quality in terms of features and amenities. However, parks in the moderately and most deprived areas also had the most safety concerns and incivilities. Although deprivation was associated with obesity, contrary to current policy guidance, both park access and quality appear less important for understanding variations in obesity within this study. Although sub-group analyses by deprivation tertile revealed that low quality park amenities in highly and moderately deprived areas may be important for understanding obesity prevalence, all other associations were non-significant.

Obesity in Scotland: a persistent inequality

BACKGROUND

Obesity is a health problem in its own right and a risk factor for other conditions such as cardiovascular disease. The prevalence of overweight and obesity increased in Scotland between 1995 and 2008 with socio-economic inequalities persisting in adults over time and increasing in children. This paper explores changes in the underlying distribution of body mass index (BMI) which is less well understood.

METHODS

Using data from the Scottish Health Survey (SHeS) between 1995 and 2014 for adults aged 18-64 years, we calculated population distributions for BMI for the population overall, and for age, sex and deprivation strata. We used SHeS data for children aged 2-15 years between 1998 and 2014, in addition to data from the Child Health Systems Programme (CHSP) collected from primary one (P1) children in participating local authorities, to describe the overall trends and to compare trends in inequalities by deprivation strata.

RESULTS

Amongst adults, the BMI distribution shifted upwards, with a large proportion of the population gaining a small amount of weight between 1995 and 2008 before subsequently stabilising across the distribution. In men the prevalence of obesity showed a linear deprivation gradient in 1995 but over time obesity declined in the least deprived quintile while the remaining four quintiles converged (and stabilised). In contrast, a persistent and generally linear gradient is evident among women for most of the 1995-2014 period. For those aged 2-15 years, obesity increased between 1998 and 2014 for the most deprived 40% of children contrasted with stable trends for the least deprived. The surveillance data for P1 children in Scotland showed a persistent inequality between 2005/06 and 2014/15 though it was less clear if this is widening.

CONCLUSIONS

The BMI distribution for adults increased between 1995 and 2008 with a large proportion of the population gaining a small amount of weight before stabilising across the distribution. Inequalities in obesity persist for adults (with different underlying patterns evident for men and women), and may be widening for children. Actions to reduce the obesogenic environment, including structural changes not dependent on individual agency, are urgently needed if the long-term health, social and inequality consequences of obesity are to be reduced.

Comparing trends in mortality from cardiovascular disease and cancer in the United Kingdom, 1983-2013: joinpoint regression analysis

BACKGROUND

We aimed to study the time trends underlying a change from cardiovascular disease (CVD) to cancer as the most common cause of age-standardized mortality in the UK between 1983 and 2013.

METHODS

A retrospective trend analysis of the World Health Organization mortality database for mortality from all cancers, all CVDs, and their three most common types, by sex and age. Age-standardized mortality rates were adjusted to the 2013 European Standard Population and analyzed using joinpoint regression analysis for annual percent changes.

RESULTS

The difference in mortality rate between total CVD and cancer narrowed over the study period as age-standardized mortality from CVD decreased more steeply than cancer in both sexes. We observed higher overall rates for both diseases in men compared to women, with high mortality rates from ischemic heart disease and lung cancer in men. Joinpoint regression analysis indicated that trends of decreasing rates of CVD have increased over time while decreasing trends in cancer mortality rates have slowed down since the 1990s. The lowest improvements in mortality rates were for cancer in those over 75 years of age and lung cancer in women.

CONCLUSIONS

In 2011, the age-standardized mortality rate for cancer exceeded that of CVD in both sexes in the UK. These changing trends in mortality may support evidence for changes in policy and resource allocation in the UK.

The idea of uniform change: is it time to revisit a central tenet of Rose's "Strategy of Preventive Medicine"?

A mean-centric view of populations, whereby a change in the mean of a health variable at the population level is assumed to result in uniform change across the distribution, is a core component of Geoffrey Rose's concept of the "population strategy" to disease prevention. This idea also has a critical role in Rose's observation that individuals who are considered abnormal or sick (the rightward tail of the distribution) and those who are considered normal (the center) are very closely related, and that true preventive medicine must focus on shifting the normal or average. In this Perspective, we revisit these core tenets of Rose's concept of preventive medicine after providing an overview of the key concepts that he developed. We examine whether these assumptions apply to population changes in body mass index (BMI) and show that there is considerable evidence of a widening of the BMI distribution in populations over time. We argue that, with respect to BMI, the idea of using statistical measures of a population solely on the basis of means and the assumption that populations are coherent entities that change uniformly over time may not fully capture the true nature of changes in the population. These issues have important implications for how we assess and interpret the health of populations over time with implications for the balance between universal and targeted strategies aimed at improving health.

Modelling obesity trends in Australia: unravelling the past and predicting the future

BACKGROUND/OBJECTIVES

Modelling is increasingly being used to predict the epidemiology of obesity progression and its consequences. The aims of this study were: (a) to present and validate a model for prediction of obesity among Australian adults and (b) to use the model to project the prevalence of obesity and severe obesity by 2025.

SUBJECTS/METHODS

Individual level simulation combined with survey estimation techniques to model changing population body mass index (BMI) distribution over time. The model input population was derived from a nationally representative survey in 1995, representing over 12 million adults. Simulations were run for 30 years. The model was validated retrospectively and then used to predict obesity and severe obesity by 2025 among different aged cohorts and at a whole population level.

RESULTS

The changing BMI distribution over time was well predicted by the model and projected prevalence of weight status groups agreed with population level data in 2008, 2012 and 2014.The model predicts more growth in obesity among younger than older adult cohorts. Projections at a whole population level, were that healthy weight will decline, overweight will remain steady, but obesity and severe obesity prevalence will continue to increase beyond 2016. Adult obesity prevalence was projected to increase from 19% in 1995 to 35% by 2025. Severe obesity (BMI>35), which was only around 5% in 1995, was projected to be 13% by 2025, two to three times the 1995 levels.

CONCLUSIONS

The projected rise in obesity severe obesity will have more substantial cost and healthcare system implications than in previous decades. Having a robust epidemiological model is key to predicting these long-term costs and health outcomes into the future.