The body's arteries become stiffer after middle age if a person has too much body fat, a new study has found.

According to UK scientists, while obesity is known to increase the risk of heart disease, the reasons for this have been so far unclear.

However, they have discovered that while the blood vessels of young obese people seem to be able to compensate for the effects of having too much weight, this does not continue and after middle age, the arteries become stiffer as body fat increases.

The study involved 200 people who were scanned in order to measure the speed of blood flow in the aorta, which is the biggest artery in the body.

It found that the arteries of young adults with more body fat were less stiff. However, from the age of 50, arteries became stiffer as body fat increased.

Furthermore, the scientists found that body fat was more associated with stiffer arteries than body mass index (BMI), which just takes into account a person's height and weight.

"The effects of having more fat seem to be different depending on your age. It looks like young people may be able to adapt to excess body fat, but by middle age the cumulative exposure to years of obesity may start to cause permanent damage to the arteries," commented lead scientist, Dr Declan O'Regan, of Imperial College London.

He said that they are unsure how body fat makes the body's arteries stiffer, ‘but we do know that certain metabolic products in the blood may progressively damage the elastic fibres in our blood vessels'.

"Understanding these processes might help us to prevent the harmful effects of obesity," he added.

Details of these findings are published in the journal, Hypertension.