TOO much exercise can damage teen health, say experts.

A study found that over exercising is just as bad for teenagers as too little, with a guideline for teens of 14 hours a week.

Regular exercise is known to have a positive impact on mental and physical well being, reducing stress and anxiety and boosting self esteem and brain power.

But experts say any more than 17.5 hours a week has a detrimental effect.

The study, carried out by Swiss scientists, involved more than 1200 teens over one year.