WASHINGTON — About one in five Americans age 12 and over suffers from hearing loss in at least one ear that is severe enough to interfere with daily communication, US researchers said Monday.

The estimate is the first to cover the entire United States instead of select populations according to location or age, said the study authors from Johns Hopkins University.

"I couldn't find a simple number of how common hearing loss is in the US," said lead author Frank Lin, an assistant professor in the department of otolaryngology. "So we decided to develop our own."

The findings, published in the November 14 issue of the Archives of Internal Medicine, a publication of the Journal of the American Medical Association, are higher than previous estimates of 21 to 29 million people with hearing loss.

The researchers took data from the National Health and Nutritional Examination Surveys (NHANES), which has tracked Americans' health since 1971, and analyzed data from just over 7,000 hearing tests between 2001 and 2008.

Forty-eight million people, or 20.3 percent of people 12 and over in the United States, have hearing loss in at least one ear; while 30 million, or 12.7 percent of the population, has it in both ears, they found.

The researchers defined hearing loss as being unable to hear speech sounds of 25 decibels or less, which is the World Health Organization (WHO) definition for hearing loss.

Hearing loss becomes more frequent as people age, but the researchers found that it tended to happen less often in women than in men, and was also less frequent in blacks than whites.

Researchers are not sure why, but they suggested that the potential protective effects of the female hormone estrogen and the skin pigment melanin should be investigated as potential reasons.

According to the WHO, about 278 million people worldwide suffer from moderate to profound hearing impairment, or about four percent of the world population.

Hearing loss can be caused by a variety of factors, including infectious disease, loud noises, injury and simple aging. About half of all cases are preventable through prevention and early diagnosis, the WHO said.