A Minnesota Department of Health analysis of possible health effects from wind turbines concludes that annoyance and diminished quality of life are the most frequent complaints from nearby residents.

The "white paper," a review of available scientific research, notes that people vary greatly in their sensitivity to noise, with penetrating, low-frequency sounds posing the most problems.

Distance helps dampen annoying or possibly harmful effects, the report concluded.

"Beyond a half mile the likelihood of impacts is fairly low in most terrains," said Rita Messing, an author of the report and supervisor of the health department's site assessment program.

Minnesota's minimum setback requirement for wind turbines is at least 500 feet or a distance that would not allow nighttime noise levels above 50 decibels more than half of any given hour.

North Dakota has used as its "informal" setback requirement a minimum distance of 1,400 feet, about a quarter of a mile. The North Dakota Public Service Commission plans to conduct hearings to evaluate a formal standard.

Clay County is considering a new zoning ordinance with a minimum setback of 1,500 feet or a distance that would not allow nighttime noise levels above 45 decibels.

"It is an issue," Tim Magnusson, the Clay County planning director, said of noise and health complaints stemming from large wind turbines, including headaches, dizziness and sleep disturbance.

The proposed longer setback, he said, is intended "as an effort to mitigate some of those issues." The county has jurisdiction to site small wind projects, capable of generating fewer than 5 megawatts.

The review by Minnesota health officials was partly in response to concerns raised by Clay County residents.

Per and Sandra Anderson, who live in Moorhead and own land in rural Clay County near the proposed Lakeswind Wind Power Plant, have asked for a thorough review of possible health effects from wind turbines.

The Minnesota Department of Health review makes clear that the effects of low-frequency vibration are not well understood, and many uncertainties remain, Per Anderson said.

The National Research Council, which has called for further research, concluded that noise produced by wind turbines generally is not a major concern beyond a half mile.

Meanwhile, some foreign experts, including the French Academy of Medicine, have called for a minimum setback of a mile, Per Anderson said.

"To me it's an indication that there's concern from the scientific community and industry doesn't get it," he added.

Anderson, a religion professor whose specialty is ethics, said officials shouldn't wait for research to be clear when human health is at stake.

Officials, he said, should take a precautionary approach in regulating wind turbines, which is increasingly the trend in Europe.

"I don't think that's morally responsible given the evidence," Anderson said of waiting to impose longer setbacks for wind turbines. "I'm arguing for better safe than sorry."

Messing said any health effects from wind turbines are "probably a fairly low-level health issue," but because effects appear quite variable no one could predict who would be affected.

That must be balanced with economic benefits, including revenues for schools, that local communities must consider, she said. A half mile, she said, "is a rather large distance," and noted most jurisdictions allow turbines much closer to residents.

On the other hand, she noted that low-frequency noise, often pulsing, can penetrate buildings. "So that's an issue."