Sealing up houses to improve energy efficiency also traps more radon inside and may lead to a higher risk of lung cancer, according to a new study, Newsmax Health reports. 

Guidelines suggest people install ventilation systems when they try to reduce heat loss from their homes.

Many energy efficiency measures, like putting draft strips along doorframes, reduce air exchange, study author Paul Wilkinson said.

Radon, a gas produced from naturally occurring uranium in soil and water, is known to increase the risk of lung cancer. It is present in many homes in varying amounts.

The U.S. Environmental Protection Agency (EPA) estimates radon contributes to about 21,000 lung cancer deaths each year, mostly among people who smoke.

"Do it yourself test kits are inexpensive. If a home tests high for radon, increasing ventilation rates and/or installing a radon mitigation system will lower radon concentrations substantially," R.William Field said. He studies the health effects of radon at the University of Iowa College of Public Health in Iowa City but wasn't involved in the new study.

In the U.S. there is little awareness of the dangers of radon, he said, and only about 30 percent of homes have been tested.

According to an EPA map, states in the Midwest and New England tend to have the highest radon levels.

Homeowners should check radon levels before and after installing energy-efficiency retrofits, according to Wilkinson.