Snehal Pinto Pereira and Nina Rogers
Being obese isn’t good for us – that much we know. Among other things, if you are obese, you are more likely to have to deal with chronic health problems such as diabetes and heart disease. The proportion of children becoming obese has been increasing. Currently, one in five children in the UK are overweight or obese by the time they start school, rising to one in three by 11 years. Obesity in childhood often tracks into adulthood, so compared to older generations, today’s children are likely to spend longer periods of their life with obesity.
Knowing what this will mean for their ability later on in life to physically function, i.e. to manage simple day to day tasks such as carrying groceries or climbing stairs, is really im-portant. Yet there is little evidence on the long-term implications of obesity for subsequent physical functioning and this is something our programme of research is seeking to address. New evidence on this topic is concerning, suggesting that people who were obese from childhood have a more than double the odds of poor physical functioning when they are aged 50.
This evidence comes from the 1958 National Child Development Study (also known as the 1958 British birth cohort). It is a great source of data, as it has tracked thousands of people from when they were born in 1958 – in fact this cohort has recently celebrated turning 60. For the purposes of this research, everyone who provided information on their ability to perform the physical tasks of daily living at 50 years were included – allowing us to examine 8,674 men and women.
We were able to look at the study participants’ BMI in childhood at ages 7, 11 and 16 and again in adulthood at ages 23, 33, 45 and 50. When they were 50, participants were asked about their ability to carry out physical tasks of daily living such as bathing, dressing, carrying groceries, climbing stairs, bending, stooping or kneeling and walking moderate distances. Participants were scored, based on how limited they were in their ability to do these things, and, for the purposes of this research, those scoring in the lowest 10% were deemed to have poor physical functioning. Of these, half had trouble bending, kneeling or stooping at age 50; almost half struggled carrying their groceries and just over a quarter had difficulty bathing or dressing.
Rising obesity with age
As study participants got older, there was a steep rise in the prevalence of obesity, from just 2 per cent when participants were aged 7 in 1965 to 25 per cent by age 45 in 2003.
Obesity in adulthood was associated with poor physical functioning. For example, compared to a woman of average height (1.62cm) and weight at 23y, an 8kg higher weight was associated with a 32% elevated odds of poor physical functioning at 50.
An interesting finding was that those who were obese for longer had greater odds of poor physical functioning at 50. Compared to individuals who were never obese, obesity from childhood through to middle-age was associated with approximately two-fold higher odds of poor physical functioning; whereas, becoming obese for the first time in mid-adulthood was associated with approximately 50% higher odds. A likely explanation of these findings is that those who were obese for longer had higher BMIs at 50 which are particularly detrimental for physical functioning.
Being inactive in adulthood
Having established links between obesity across the life-course and poor physical functioning at 50, we turned our attention to the role of inactivity to see whether it might be a potential key area of focus for intervention.
People who are obese tend to be less active. We simulated what might happen to the relationship between obesity and poor physical functioning if activity levels among obese people were increased to be in line with activity levels among the non-obese. Our motivation was to understand the benefits of reducing inactivity among individuals who are obese as a way of promoting independence at older ages.
This research made use of the 1958 cohort study and its earlier counterpart, the MRC National Survey of Health and Development, which started in 1946. Examining data from these two oldest British birth cohorts that have been conducted in broadly comparable ways was a key strength of the study, allowing us to assess whether findings were similar across generations. We looked at over 11,000 individuals. Most (approximately 68 per cent) had not been obese in adulthood, 16-30 per cent became obese and approximately 11 per cent of those born in 1958 and 5 per cent of those born in 1946 were obese throughout adulthood.
As in the earlier research, there was a strong link between being obese in adulthood – at any age, and having poorer physical functioning later on. Similar to our findings in the 1958 cohort, we saw in the 1946 cohort, a trend between longer periods of life that participants were obese and higher chances of poorer physical functioning later in life. For example, obesity onset from the mid-30s was associated with approximately a three-fold higher risk of poor physical functioning in the early 60s, and obesity onset in the mid-40’s was associated with a two-fold higher risk.
Despite a link between obesity and inactivity, and also between inactivity and poor physical functioning, we found little change in the relationship between obesity and poor physical functioning. Our findings suggest that, in terms of reducing the risk of poor physical functioning, the benefits of reducing inactivity among people who are obese is limited. This demonstrates clearly the need to focus on preventing and delaying the onset of obesity to help people to function physically later on.
In addition, the research shines a light on what the future holds. If current obesity trends continue, higher proportions of younger generations will be obese from at least as early as mid-adulthood and worryingly, the work suggests that much of this future adult population will be at risk of poor physical functioning before reaching older ages.
The causes of obesity are complex and multi-factorial, with the outgoing Chief Medical Officer recently calling for radical changes to tackle childhood obesity. Our work highlights the importance of averting obesity and importantly suggests that interventions and policies need to start at young ages and continue throughout life.
With their daily contact with individuals in the community, healthcare professionals could routinely provide information and advice around healthy lifestyles and, where appropriate, refer to weight management services. It goes without saying that these are often hard-pressed people working long hours and that any proposed interventions would need to take this into consideration and be properly planned, financed and supported.
Snehal Pinto Pereira is a Career Development Fellow in the Department of Epidemiology and Public Health at UCL. Nina Rogers is a Research Associate in the Department of Epidemiology and Public Health at UCL. Adult obesity and mid-life physical functioning in two British birth cohorts: investigating the mediating role of physical inactivity is research by Snehal M Pinto Pereira, Bianca L De Stavola, Nina T Rogers, Rebecca Hardy, Rachel Cooper and Chris Power and is published in the International Journal of Epidemiology.
Image: Ruud Koot