Even people who appear to be in good health should be aware of the warning signs for Parkinson's disease, according to experts.

Constipation, (characterized as a frequency of less than twice per week), loss of the sense of smell, sleep disorders, slowness of movement, tremors or rigidity are all preclinical symptoms of the disease, said Wing Yun-kwok, chairman of the Department of Psychiatry at the Chinese University of Hong Kong's Faculty of Medicine.

Anne Chan Yin-yan, head of the Parkinson's Disease and Movement Disorder Unit at CUHK, said, "Identifying Parkinson's disease at an early stage and intervening when the neurodegeneration is less severe provides a higher chance of slowing the progression and even preventing the development of disabling symptoms."

The website of the American Parkinson's Disease Association states that the symptoms can broadly be divided into two categories. They are motor - including slow movement, rigidity and tremors - and nonmotor, such as sleep disorders and constipation. Studies show that nonmotor symptoms can precede motor symptoms by decades.

"When those motor symptoms appear, around 50 percent to 80 percent of relative nerve cells have already been lost," Chan said.

According to Zhang Zhenxin, chief physician in the Department of Neurology at Peking Union Medical College Hospital in Beijing, even though it is essential to consult a doctor in the initial stages, studies show that nearly 15 percent of Parkinson's patients on the Chinese mainland didn't seek medical help until two years after the disease took hold.

That is because the early symptoms are almost imperceptible and the disease progresses slowly. Moreover, the early stages can easily be confused with the normal effects of ageing.

Although there is no cure for Parkinson's, it is still important to receive formal treatment in the early stages.

"Research has shown that patients who received treatment within three years of the appearance of symptoms show better self-care ability, mobility and quality of life than those who received treatment four years after the onset of the disease," Zhang said.

Almost half of the people with Parkinson's in the world are Chinese, according to a study by the University of Rochester in the United States in 2007.

Based on a national epidemiological survey, the estimated morbidity of Parkinson's patients age 65 and older is 1.7 percent in China, and there are more than 2.5 million people with Parkinson's on the mainland.

With 100,000 new cases each year, the number of patients on the mainland will reach 15 million by 2030.

Specialist outpatient clinics are being established nationwide to ward off the disease. To date, there are 500 in 150 cities and counties, providing timely, efficient treatment.

A new edition of a guide book about Parkinson's clinics was published last month, providing patients with the addresses of facilities in their area and details that allow them to make appointments for consultations via their mobile phones.

After Alzheimer's disease, Parkinson's is the second most-common neurodegenerative disease in Hong Kong, which has an estimated 12,000 patients, according to CUHK.