I know summer is coming to New York when I start seeing groups of people, both women and men, practicing folk dance in Central Park or in other open spaces in the city. I am always amazed by their enthusiasm, because although many among them are not young, they put a lot of energy and enthusiasm into this activity.

Similar groups can also be seen in many Chinese cities, where guangchangwu, which can be translated as "square dancing" is an activity engaged in by mostly groups of middle aged and elderly people, a majority of whom are women. According to some estimates, there are about 100 million square and folk dancers in China.

In most cases, dancers gather early in the morning or in the evening, and dance to the sound of loud music to keep fit and engage in some refreshing recreation. Their activity, however, doesn't meet with the approval of many of their neighbors, who complain about the loud music, nay the noise, they cause, saying it is a source of irritation.

Many neighbors have demanded that dancing in public squares and parks be banned to prevent it from becoming a more critical problem in the neighborhoods where it is practiced. As a response, lawmakers in Guangzhou, Guangdong province, have drafted a law that would set limitations on square dancing in order to create quieter public areas for everybody's enjoyment. According to the proposed law, expected to be implemented by the end of this year, people who violate it could be fined up to 2,000 yuan ($322.52).

Physical activities, including dancing and exercise, have proved increasingly effective in reversing some of the effects of aging. These activities are also an effective way of keeping people more aware, having better memory and even delaying some of the negative traits of diseases such as Alzheimer's and other forms of dementia which are becoming more frequent today as people live longer.

The Einstein Aging Study, whose summary was published in the New England Journal of Medicine, one of the leading medical journals in the US, found that dancing helps prevent both Alzheimer's disease and vascular dementia, the second most common form of dementia after Alzheimer's disease. The study included people taking part in 11 other physical activities such as team sports, swimming and cycling. Of all the physical activities, however, only dancing benefited the brain, which researchers believe is the result of the cerebral rather than the physical aspect of dance.

Joseph Verghese, the lead researcher of the study, said: "Dance is not purely physical in many ways, it also requires a lot of mental effort. Among the people who participated in the Einstein Aging Study, those who danced frequently--three or four times a week -- showed 76 percent less incidence of dementia than those who danced only once a week or didn't dance at all. Other studies have concluded that dance has social and emotional elements that are advantageous for all people, but particularly for those who want to lead long and healthy lives.