This "profound effect" of obesity, however, could be curbed by losing weight, the study showed.

The study, presented at the European Congress on Obesity (ECO) in Venice, Italy, for the first time, quantified the impact of age of onset, severity, and duration of childhood obesity.

"The early onset obesity model shows that weight reduction has a striking effect on life expectancy and comorbidity risk, especially when weight is lost early in life," Dr Urs Wiedemann of Stradoo GmbH, a life sciences consultancy in Munich, Germany.

"It is clear that childhood obesity should be considered a life-threatening disease. It is vital that treatment isn't put off until the development of Type 2 diabetes, high blood pressure or other 'warning signs' but starts early," Dr Wiedemann said.

For the study, the researchers created an early-onset obesity model based on data from 50 existing clinical studies on obesity and obesity-related comorbidities, such as type 2 diabetes, cardiovascular events, and fatty liver.

The studies included more than 10 million participants from countries around the world, approximately 2.7 million of whom were aged between 2 and 29 years.

The results also showed that a 4-year-old child with a body mass index of 3.5 (which indicates severe obesity) and who doesn't go on to lose weight has a 27 per cent risk of developing diabetes by the age of 25 and a 45 per cent risk by the age of 35.