A new study revealed that the age-adjusted prevalence of any sleep disorder diagnosis among U.S. military veterans have risen by 600 percent over an 11-year period.

The study, published in the journal Sleep, showed that the age-adjusted prevalence of sleep disorder among U.S. veterans have increase to nearly 6 percent in 2010 from the less than 1 percent in 2000.

For the study, the researchers analyzed a total sample of 9,786,778 veterans seeking care in the Veterans Health Administration system between 2000 and 2010. The researchers accessed the national Veterans Administration Informatics and Computing Infrastructure database for the electronic medical records of the veterans. The then defined the cases using diagnostic codes specified by the American Academy of Sleep Medicine.

Among those, 751,502 were diagnosed with at least one sleep disorder. The researchers summarized age-adjusted annual prevalence by sex, race, combat exposure, body mass index, and comorbid diagnoses.

Sleep apnea is the most common sleep disorder to be diagnosed, with 47 percent of the study sample, followed by insomnia with 26 percent.

Sleep apnea is a common sleep disorder that occurs when an individual experiences one or more pauses in breathing or shallow breaths during sleep. These breathing pauses may last from a few seconds to minutes and may occur 30 times or more within an hour.

On the other hand, insomnia is a persistent sleep disorder that makes it hard for an individual to fall asleep, stay asleep or both. People with insomnia often awaken feeling unrefreshed and tired.

According to a press release, the prevalence rate of veterans suffering from post-traumatic stress disorder (PTSD) has tripled within the 11-year study period. Additionally, 16 percent of veterans with PTSD were diagnosed with sleep disorder, the highest among various health conditions.

Meanwhile, veterans diagnosed with cardiovascular disease, cancer, or other chronic diseases were more likely to develop sleep disorders relative to those without comorbid conditions.