A study published in the New England Journal of Medicine has found that children who were obese were almost twice as likely to die before 55 years of age than those who were not obese. Moreover, children whose weight was in the top 25% out of nearly 5,000 kids were 2.3 times more likely to die from diseases before middle age than those whose weight fell in the bottom 25%.

The authors of this big, long study looked at body mass index (BMI; a measure of weight that takes into account a person’s height) and risk factors for cardiovascular disease in 4,857 children aged 5-19 years who lived on an American Indian reserve in Arizona.

BMI and markers of cardiovascular disease were measured in all children when the study started in 1966 or after. The participants were then followed up until their death, their 55th birthday, or the end of 2003, whichever came first.

A total of 559 (11.5%) participants died before the age of 55, 166 (3.4%) of whom died from a disease or from self inflicted injury such as alcohol or drug abuse – so-called “endogenous causes.”

Children whose BMI fell within the top 25% of all those in the study were 2.3 times more likely to die from endogenous causes before the age of 55 than those whose BMI was in the lowest 25%. In fact, each one unit increase in BMI increased the risk of early death from endogenous causes by 40%.  This relationship persisted but at a slightly lower level once factors like cholesterol level and blood pressure were taken into account.

The authors then looked specifically at the 1394 (28.7%) children who were obese – those whose BMI fell in the top 5% on growth charts from governmental public health body the Centers for Disease Control and Prevention. Compared with non-obese children, these kids were 31% more likely to die before they reached 55.

Children with high blood glucose levels – a sign that diabetes might be on the horizon – were at 73% higher risk of dying early, whereas those with hypertension were at 57% higher risk. This link prompted the authors to say that the link between obesity and premature death “may be partially mediated by the development of glucose intolerance and hypertension in childhood.”

Childhood cholesterol level and blood pressure, however, had no effect on the risk of premature death from endogenous causes.

Speaking to the New York Times, senior author Helen Looker said, “This suggests that obesity in children, even prepubescent children, may have very serious long-term health effects through midlife — that there is something serious being set in motion by obesity at early ages. We all expect to get beyond 55 these days.”

American Indians were studied because childhood obesity has been common for decades in this ethnic group. The prevalence of obesity in young Arizona Pima Indians in the 1960s, when this study was initiated, was similar to that seen in Hispanic and African American children today, so hopefully the results from this long study should be generalisable to kids today.

In a linked editorial, Edward W Gregg of the Centres for Disease Control and Prevention pointed out: “Since the trends with respect to obesity and diabetes among the Pima Indians have been a reliable harbinger for trends in the rest of the U.S. population during recent decades, the present study should intensify the debate about whether interventions that are initiated during childhood and young adulthood can affect our broader diabetes epidemic.”

Furthermore, in a previous study the same authors found that BMI correlated closely with total body fat – adiposity – and that adiposity in turn correlated with cardiovascular risk factors. By extension, the link between BMI and early death in this study suggests that actual body fat is linked with early death.

This is important because BMI is an imperfect measure of weight – for example, some very muscular people might be heavy for their height and thus have a high BMI – thus despite the study results weight might not genuinely be associated with early death. On the other hand, high adiposity – “fatness” – is a more indicative of an unhealthy weight.

“Childhood obesity is becoming increasingly prevalent around the globe. Our observations, combined with those of other investigators, suggest that failure to reverse this trend may have wide-reaching consequences for the quality of life and longevity,” conclude the study authors.

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Franks P et al. (2010) Childhood Obesity, Other Cardiovascular Risk Factors, and Premature Death. New England Journal of Medicine 362 (6): 485-493. DOI: 10.1056/NEJMoa0904130