People with sleep apnea are more likely to die in a given time period, according to a new study.

The National Institutes of Health study followed more than 1,500 adults between ages 30 and 60 for an average of 13.8 years. Those who had sleep-disordered breathing -- another name for apnea -- at the start were two to three times more likely to die from any cause.

Researchers said in a news release that the effect was tied to severity of breathing problems, but was not due to age, obesity or heart health.

Those who were not treated for their apnea were four times more likely to die from any cause and five times more likely to die from cardiovascular conditions.

The results were based on data from the Wisconsin Sleep Cohort.

A news release on the work said it is estimated that 12 million to 18 million people in the U.S. have moderate or severe breathing problems. Because affected individuals are asleep and typically unaware of the breathing problems, and the condition cannot be diagnosed during routine physician office visits, most people with sleep-disordered breathing are undiagnosed.