Improved home ventilation that dehumidifies the air may make it easier for people with asthma to breathe at night, hint findings of a small study from the United Kingdom.

In theory, lowering indoor humidity should lower concentrations of moisture-loving dust mites - a major trigger for asthma-related breathing problems.

To test this, Dr. Neil C. Thomson, at the University of Glasgow, and colleagues measured breathing patterns over 12 months in 119 men and women who were about 42 years old on average and had asthma for 9 to 30 years.

Specialists retrofitted each home with a humidity-lowering ventilation system. They also steam-cleaned carpets, and replaced mattress covers and bedding, to clear dust mites.

In half the homes the ventilation systems actively exchanged indoor and outdoor air. In the other “control group” half, the systems had operational motors but non-operational fans to help ensure the groups remained “blinded” to what was actually happening, the researchers report in the journal Allergy.

Thomson’s team found no overall difference in dust mite concentrations between the homes with and without a working ventilation system.

Also, their comparison of morning breathing tests done at the start of the study and again at 3, 6, 9, and 12 months, showed no difference between those living with or without operational ventilation.

However, participants living in homes with working ventilation systems showed an overall significant improvement in evening breathing tests, while those with non-working systems worsened in these tests.

This may be partially due to the slightly reduced humidity, and dust mite levels found in the bedrooms and bedding of participants with active ventilation systems. But ventilation may also have improved overall air quality, Thomson speculated in an email to Reuters Health.

SOURCE: Allergy, November 2009.