Residents living near wind turbines are increasingly complaining of headaches, dizziness, insomnia and other ailments, sparking fears that the new energy source could pose a risk to public health.

Although the cause of the problem remains unclear, the Environment Ministry is investigating the possibility that low frequency sounds produced by the turbines are to blame.

The ministry is concerned that reports of ill health could spread as more wind turbines are built near residential areas.

Tsuyoshi Okawa's family fell ill in January 2007 soon after wind turbines began operating at Gumihara wind farm, about 350 meters from their home in Tahara, Aichi Prefecture.

The 40-year-old says they began to lose feeling in parts of their bodies, suffered bouts of dizziness, and were unable to sleep properly.

When they spent time away from the house, the symptoms quickly dissipated. But as soon as they returned, they would flare up again.

At the family's request, a group of acoustics experts conducted noise level tests and found that low frequency sounds were causing vibrations throughout the house.

Although they advised the Okawa family that those sounds could not adversely affect their health, the family decided to rent an apartment farther away where they could go to sleep each night.

Some local residents have dubbed the ailments "wind turbine diseases."

Low frequency sounds, which measure 100 hertz or less, are difficult for humans to hear. They are typically produced by air-conditioners and factory boilers. For years, people living within the vicinity of such equipment have complained of similar illnesses.

So far, more than 70 people living near wind turbines have reported ill health. They include residents in Ikata, Ehime Prefecture; Higashi-Izu, Shizuoka Prefecture; Toyohashi, Aichi Prefecture; and Minami-Awaji, Hyogo Prefecture.

In Toyohashi, where one company already operates a wind turbine, Chubu Electric Power Co. ran into stiff opposition from local residents to its plan to build 13 wind turbines. Residents say the proposed construction site is too close to homes.

The electric power company, based in Nagoya, was eventually forced to freeze the plan.

"As there are no safety standards on low frequency sounds, we cannot obtain the understanding of local residents," an official explained.

Full-scale construction of wind turbines in Japan started in the late 1990s and quickly increased, as concern over global warming shifted international attention toward environmentally friendly energy sources. By the end of fiscal 2007, Japan had 1,409 wind turbines.

Initially, they were situated along the coastline in areas such as Hokkaido and Tohoku. As construction increased and remote locations were used up, wind farm operators began to build them near residential areas. Izu Peninsula in Shizuoka Prefecture is the site of a plan to build as many as 80 wind turbines.

"We look for places where sufficient wind blows and no residential areas are located nearby," an official of a wind farm operator said.

"But even if we find those places, they are often located in national parks. It is hard to find suitable places."

In response to nationwide concern about the environmental hazard posed by low frequency sounds from factories, stores and houses, the Environment Ministry in 2004 issued a guidebook with advice about how to cope with them.

The ministry is now studying international data showing a potential link between wind turbines and health problems in surrounding areas to determine a plan of action for Japan. It has also started measuring low frequency sounds around some wind farms.

Tomohiro Shishime, who heads the ministry's Office of Odor, Noise and Vibration, said: "From a scientific point of view, the causes of the health problems have not become clear yet. So we can't create (safety) standards (on low frequency sounds) now."

According to Izumi Ushiyama, professor of engineering at the Ashikaga Institute of Technology in Ashikaga, Tochigi Prefecture, complaints about the ill-effects of low frequency sounds are more common in Japan than in the United States or Europe because the country is small and densely populated.

Huge wind turbines also dominate the landscape, obstructing views and making local residents feel boxed in, he said.

"It is important for companies (planning to construct wind turbines) to announce their plans in early stages and obtain proper understanding from local residents," he said, adding, "The government should also tackle the issue positively."