Obese and overweight children as young as five are showing signs they could be at risk of heart attacks and stroke later in life, new research shows.

The Oxford University study found obese and overweight children had higher blood pressure than their normal-weight peers.

Obese children also had higher cholesterol and insulin levels, and a thickening of the heart muscle, compared with normal-weight children.

All these symptoms are known cardiovascular disease risk factors.

The authors of the study, published in the British Medical Journal this week, said if the risk factors continued into adulthood, obese children could be at 30 to 40 per cent higher risk of stroke and heart disease than their normal-weight counterparts.

“Weight and especially obesity has a significant effect on the risk parameters for cardiovascular disease that are present in children from age five years,” the authors said.

“This effect could give them a head start on their normal and even overweight classmates for future cardiovascular disease, diabetes and stroke.”

The impact of obesity on future health could be far greater than previously thought, the authors wrote.

The Oxford researchers analysed 63 studies involving about 49,000 children aged five to 15 from highly developed countries.

The prevalence of childhood obesity had increased significantly over the past 30 years, they said.

In 2010, about 43 million children younger than five years were overweight worldwide.

The researchers said it was necessary to pinpoint the exact age when risk factors began in children to prevent the problems occurring.

A study by researchers at Melbourne’s Murdoch Childrens Research Institute, published earlier this year, found that obesity caused fewer health problems in toddlers but started to bite in adolescence.

Lead researcher Melissa Wake said this highlighted a crucial period of time to intervene and reverse the weight problems.

Dr Robert Grenfell from the Heart Foundation said almost a quarter of Australian children were now overweight or obese.

“We’re very concerned that today’s children and teenagers could become the first generation in history to die at a younger age than their parents,” he said.

He said the Oxford research suggested obese children already had high blood pressure and cholesterol, which normally wasn’t observed until people were in their thirties or forties.