Forget taiji and qigong. A group of 20 to 50 elderly folk have picked up an unorthodox activity - all in the name of health.

Every weekday morning, they take turns rolling down a slope at Bedok Reservoir.

They are led by 71-year-old retiree Lew Keh Lam, known to the group as 'Master', who started the activity seven years ago. Mr Lew claims rolling downhill can cure all forms of ailments, including cancer, Parkinson's Disease and stroke.

"Our body is short of negative ions. In the morning, before the sun shines, there're a lot of negative ions in the grass. If your body requires the negative ions, it will allow you to roll, and when you don't need it, it won't let you roll," said Mr Lew in Mandarin.

However, general practitioner Dr Chia Ai Mian said there is no scientific evidence that Mr Lew's claims and added that the activity pose some risks.

"If they are rolling at that kind of speed they may sprain their back. They may get bruised and get cuts if they're not careful which ground they are on," said Dr Chia.