Rugao, a city renowned for the longevity of its residents, has 255 centenarians, according to statistics from the city's civil affairs bureau released Thursday.

The city with a population of 1.45 million and located in east China's Jiangsu Province, also has more than 4,000 people above 90 years old and 40,000 above 80, according to the statistics.

Rugao's average life expectancy is 75.59 -- 4.59 and 9.59 higher than the China and world average respectively.

China has six "longevity cities," but Rugao is the only one to be found in a low-lying and economically-developed region.

Regular and healthy eating and sleeping habits were believed to be the reason of people's long life in Rugao.

The favorable environment may contribute to the residents living longer as well. A study by the Jiangsu Provincial Institute of Geological Survey showed that per kilogram of soil contained an average of 3.3 milligrams of iodine, 57.3 milligrams of zinc and 0.047 milligrams of selenium, generally higher than other regions.

According to experts with the institute, selenium plays an important role in preventing humans from getting cancer, zinc is a key element in protein, while iodine is necessary in forming the thyroid hormone.

More centenarians are likely to be seen as life expectancy is expected to keep rising. Report by the World Health Organization said that by 2009, the average life expectancy in China was 73.05 years, up from 71.4 years in 2000 and 72 in 2006.