London, Aug 7 - Middle-aged smokers are 70 percent more likely to develop dementia than those who don't smoke, a new study has warned, prompting experts to advise regular physical and mental exercises.

The study published in Britain's Journal of Neurology, Neurosurgery and Psychiatry says people who smoke, have high blood pressure or diabetes massively increase their risk of developing dementia.

Under-55s who smoke increase their risk five-fold, and smokers aged between 46 and 70 have a 70 percent higher risk of developing chronic memory loss, according to the study.

Diabetes will more than triple the risk of dementia, says the study.

A separate study published this week in the American journal Neurology shows that people may be able to ward off the onset of dementia by stimulating their brain regularly through everyday activities such as reading, writing and playing card games.

Dr Susanne Sorensen, head of research at Britain's Alzheimer's Society, said: 'Interestingly this research has found that memory loss in people who are in the very early stages of the condition may be delayed by ordinary activities that engage the brain, whether they were well-educated in early life or not.

'This research suggests that exercising your brain as well as your body may play a role in the fight against dementia.'

The results in the British journal show that middle-aged people should immediately quit smoking and make lifestyle changes that will help control dementia rather than waiting until they are pensioners.

'A healthy heart means a healthy brain,' said Neil Hunt, Chief Executive of Alzheimer's Society, adding that people should keep active, eat a balanced diet, not smoke and have their blood pressure and cholesterol checked regularly.