You might want to put this to the back of your mind until after Christmas, but an unhealthy lifestyle could make you look a year older, new research suggests.

Scientists have found that high blood sugar levels, associated with unhealthy living and lack of exercise, could cause the face to age more quickly.

Researchers measured the blood sugar of 602 people. A further group of 60 participants were then asked to study two photographs of their faces and score them with a "perceived age".

It was found that the healthy people with low blood sugar looked on average a year younger than those with high levels, and as much as 18 months younger than diabetics.

It was calculated that every additional millimole per litre increase in blood sugar added five months of ageing to their facial features.

One theory is that the build-up of sugar sticks to collagen, a protein that helps to keep skin supple, and becomes difficult to remove.

Another suggestion is that glucose could hamper insulin production, which is thought to play a significant role in the ageing process.

David Gunn, who led the Unilever study, said: "The higher glucose people had, they started looking older. Diabetics looked older again, and they have had the worst exposure to high glucose levels.

"This adds extra evidence that there is another reason to have a healthy lifestyle – because it is going to affect your appearance as well as your health."