A Canadian researcher says ultraviolet light can zap harmful microbes to prevent headaches, sore throats, itchy eyes and other symptoms that might be attributed to allergies in office workers.

The glass and steel facades of modern buildings seem impenetrable. Windows are sealed shut to keep heating and cooling costs down, but the conditions can lead to "sick building syndrome."

Dr. Dick Menzies of the Montreal Chest Institute wanted to see if office worker ailments could be improved using ultraviolet light to kill bacteria and mold.

His team installed UV lights in the ventilation systems of three buildings in downtown Montreal. The lamps were aimed at the cooling coils and drip pans in ventilation systems, where the germs collect.

It's estimated more than two-thirds of North Americans work in air-conditioned buildings.

"What we're trying to do is exactly what the sun does. You never see bacteria or mould growing in sunlight," said Stuart Engel, president of the Montreal company that makes the filters

Over a year, 771 employees filled out questionnaires about their sick building syndrome complaints.

"Overall, there was about a 20-per-cent reduction in symptoms, particularly in symptoms that might be attributed to allergy, for example nose irritation, congestion, itchy watery eyes, sore throat," said Menzies.

He notes the reduction was small since the air inside offices still had a high microbial count because humans themselves carry germs. Diseases also spread through personal contact and on transit.

Ultraviolet cleansing may not be a cure-all for indoor bacteria, but the study suggests it goes a long way toward helping office workers breathe easier.

The study, which appears in this week's issue of the medical journal The Lancet, is the first large-scale look at the effect of UV radiation on the health of office workers.

More research is needed to confirm its effectiveness before building owners start to think about installing the systems. Engel said the filters will cost about $50,000 for a large building.