The EarlyBird Study – Key Findings to October 2008
EarlyBird is a focused cohort study, monitoring the causes and behaviour of insulin resistance in contemporary children. Insulin resistance, largely the result of obesity, is believed to underpin the development of diabetes and cardiovascular disease that characterises modern society. EarlyBird is distinctive in combining objective measures of physical activity and body composition from the age of 5y with annual fasting blood samples which reach beyond simple body composition (BMI and body fat) to metabolic health (insulin sensitivity, blood fats, cholesterol, blood pressure). The study is generating some novel and sometimes counter-intuitive findings, which have nevertheless withstood the rigours of peer review – over 30 reports are now in print. It currently has eight annual data sets from 5y to 12y and retains nearly 80% of the original cohort. If funded, the study will continue into young adulthood. The highlights are summarised here.
The Obesogenic Environment
- There was evidence in the past of a relationship between low birth weight and diabetes risk – with the result that parents have been encouraged to feed up low birth weight children. However, EarlyBird no longer finds an association between insulin resistance in childhood and birth weight. The association – and a strong one – now lies with excess weight gain in early childhood. This raises an important public health issue – the importance of keeping weight low in children of low birth weight, because excess weight gain in childhood is associated with high insulin resistance (Wilkin TJ – Diabetes 2003).
- Overweight is now perceived as the norm. Parents are no longer aware of their own or their children’s obesity. A simple analysis of the EarlyBird parents and their children revealed what is a fundamentally serious issue for the campaign to reduce childhood obesity. Parents are essential partners in the fight against childhood obesity yet, crucially, they do not acknowledge the problem. (Jeffery AJ – BMJ 2005).
- Despite clear evidence of an SES gradient in sports club attendance among the children, EarlyBird can find no evidence for corresponding differences in physical activity. The same is true for family income. The assumption that children of lower socio-economic status suffer from their lack of structured opportunity with less physical activity is not reflected in the evidence. Indeed, analysis suggests that the poorer child may undertake marginally more, rather than less, physical activity than the wealthier. (Voss LD – Child Care, Health and Development 2008)
- Girls are genetically some 35% more susceptible to diabetes than boys – hotly contested when first published, but now widely accepted. Young overweight females may be more important to target for obesity prevention than males, as they consistently develop type 2 diabetes more often. (Murphy MJ – Pediatrics 2004).
- Girls are born lighter than boys – a finding that is universal throughout the human race, and by implication likely to confer survival advantage on the species. Birth weight is mostly related to growth during the third trimester of gestation, and this in turn to levels of foetal insulin. EarlyBird proposes that the insulin resistance that makes females more susceptible to diabetes may also be responsible for their lower birth weight. Finding the gene responsible (by implication sex-linked) could unlock a mechanism that controls insulin resistance, the basis for type 2 diabetes. (Wilkin TJ – Int J Obesity 2006).
The Accelerator Hypothesis
- The incidence of type 1 diabetes is rising as fast as type 2, and both in parallel with obesity. The Accelerator Hypothesis, which underpins the EarlyBird study, proposes that type 1 and type 2 diabetes are the same disorder of insulin resistance set against different genetic backgrounds. The implications are important to type 1 diabetes prevention programmes which might consider lifestyle change before embarking on immunotherapy or islet cell transplant. An RCT to test the hypothesis is the subject of a grant application to the EME programme of the NIHR. (Wilkin TJ – Diabetologia 2001).
- Support for the principal prediction of the The Accelerator Hypothesis, that among children who develop Type 1 diabetes, those of higher body mass index (BMI) will develop it younger – true acceleration. (Kibirige M – Diabetes Care 2003; Editorial by Arlan Rosenbloom, same issue)
- Independent support for the Accelerator Hypothesis, including evidence that waist circumference is greater in children who develop type 1 diabetes. It satisfies another prediction that BMI at presentation will rise as the environmental accelerator (body mass) increases over time. (Betts P – Diabetic Medicine 2005; editorial by Dennis Daneman, same issue).
- A closely reasoned plea, with a group of international opinion leaders, to consider lifestyle change or insulin sensitising drugs (as proof of principle) in the prevention/management of Type 1 diabetes. Weight gain appears to be an important environmental accelerator contributing to the increase in Type 1 as well as type 2 diabetes, and lifestyle intervention, clearly effective in Type 2 diabetes, should now be trialed in Type 1 before embarking on further trials using more aggressive forms of treatment . (Wilkin TJ – Diabetes Care 2004)
Physical Activity/The Activitystat Hypothesis
- The UK and US Governments advise at least 60 minutes moderate physical activity every day. This report reveals the strengths of a truly longitudinal design, reaching beyond cross-sectional analyses to establish what proportion of children consistently meets the guideline, and what the impact of doing so is on change in body composition and metabolic health. Only 42% of the EarlyBird boys and 11% of the girls met this guideline consistently over the three-year period from 5-8 y. Importantly (because governments use BMI as their outcome measure), there were no differences in the trend for BMI over the four time points in either sex, but the more active children were metabolically healthier. The study questions the utility of BMI as the outcome measure of physical activity programmes in children, whether the bar for girls should be lowered (girls systematically record less physical activity than boys) and whether it is possible to achieve more activity in less active children. (Metcalf BS – Arch Dis Child 2008).
- Less than 1% of the four-fold variation in physical activity among children can be explained by the five-fold variation in PE opportunity at school. This study, more than any other, points to the lack of environmental impact on the physical activity of children, and asks what effect Government policy on expanding recreational facilities might have on children’s activity. The report was based on a single school term. We have recently been funded to analyse the remaining three terms’ data from this study, which will allow us to assess year-on-year reproducibility and control for effects of seasonality. (Mallam KM – BMJ 2003).
- Being driven to school may not be eco-friendly, but it does not appear to reduce a child’s overall activity – he/she makes up for it elsewhere in the day. The activity cost at 7y of being driven to and from school during the hours 8-9am and 3-4pm is 16%, but overall nil. (