A new study has questioned why poorer children are at higher risk of obesity compared to their better-off peers. The findings are published in The European Journal of Public Health.

Researchers from University College London and London School of Economics used data from the Millennium Cohort Study (MCS). This tracks nearly 20,000 families from across the UK. This study used measurements made when the children were aged 5 and again at age 11.

The link between relative poverty and childhood obesity was stark. At age 5, poor children were almost twice as likely to be obese compared with their better off peers. 6.6% of children from families in the poorest fifth of the sample were obese while the figure for the richest fifth is just 3.5%. By the age of 11 the gap has widened, nearly tripling to 7.9% of the poorest fifth are obese; for the best-off, the figure is 2.9%.

The researchers examined many aspects of a child's environment and health behaviours. The environmental factors looked at were aspects such as whether the mother smoked during pregnancy, how long she breastfed for and whether the child was introduced to solid food before the age of four months. They also factored in the degree to which the mother was herself overweight or obese. senior author Professor Yvonne Kelly explained that: "intervening in the early years when the family environment has more profound influences on children's healthy development has the potential to be particularly effective."

To assess the impact of physical behaviour, the study compared the frequency of sport or exercise, active play with a parent, hours spent watching TV or playing on a computer, journeys by bike and the time that children went to bed. It also compared dietary habits such as whether the child skipped breakfast as well as fruit and sweet drink consumption. Professor Kelly went on to stress that:

"The 'structural' causes of socioeconomic inequalities have to be addressed along with tackling 'inherited' obesity via lifestyle factors that tend to go with lower incomes. Early intervention with parents clearly has huge potential. And evidence from our work suggests that this should start before birth or even conception."

The study found that doing sport more than three times a week played an important role, as did an earlier bedtime and regular fruit consumption which were both positively associated with downward movement in weight categories. However, maternal smoking during pregnancy and a mother's BMI were negatively associated with downward movement across weight categories. Overall, the study found that markers of 'unhealthy' lifestyle here could mean as much as a 20% additional risk of obesity for a child.

The analysis in this study suggests better targeting. The authors say that more research should be undertaken to increase effectiveness, given that the processes involved in the development of fat gain in children involve social, environmental, and biological factors.