If you have continuous ringing in your ears or some other phantom noises -- known medically at tinnitus -- think about another cup of morning coffee as a possible treatment, researchers say.

Although the exact mechanism is as of yet unknown, a study found women who reported they consumed higher-than-average levels of caffeine were found less likely to experience the steady buzzing or ringing of the ears associated with the condition.

The study began in 1991 with around 65,000 American women with no reported incidence of tinnitus, and followed them for 18 years during which time almost 5,300 subsequent cases of tinnitus were recorded.

If a participant reported either daily symptoms or occurrences a few days a week, the study researchers considered that a case of tinnitus.

During the course of the study, the researchers gathered information on the participant's medical history, diet and lifestyle.

Analyzing their data, the researchers found women who consumed less than 150 milligrams of caffeine daily -- equivalent to about one-and-a-half 8-ounce cups of coffee -- had a 15 percent greater chance of developing tinnitus than women whose caffeine consumption was between 450 mg to 600 mg each day.

The study results are not proof of a cause-and-effect relationship between caffeine and tinnitus, the researchers acknowledged, and they said that further research is needed to understand the results.

"We know that caffeine stimulates the central nervous system, and previous research has demonstrated that caffeine has a direct effect on the inner ear in both bench science and animal studies," says researcher Dr. Gary Curhan, a professor of medicine at Harvard Medical School in Boston.

However, he says, "The reason behind this observed association is unclear."

Around 50 million people in the United States suffer from some degree of tinnitus, according to the American Tinnitus Association.

Although those afflicted most often describe a ringing sound, some people report hearing hissing, clicking, roaring, buzzing or chirping noises.

It is generally considered not a condition in itself but rather a symptom of some underlying medical problem, such as injury, a circulatory system disorder or age-related hearing loss.

Tinnitus should be of sufficient concern to merit a doctor's examination it if interferes with daily routines, if it occurs suddenly or without apparent cause or is accompanied by dizziness or hearing loss, the Mayo Clinic says.

The new study, conducted by Harvard researchers working with the Brigham and Women's Hospital in Boston, was published in the American Journal of Medicine.