A Swedish study which linked heavy use of wireless phones with an increased chance of brain cancer has been questioned by the US Food and Drug Administration (FDA).

Reported on March 31 in the International Archives of Occupational and Environmental Health, the study was conducted by researchers at the Swedish National Institute for Working Life.

After comparing data from 2,200 cancer patients and an equal number of healthy patients, researchers found those who heavily used cellular phones had a 240 percent increased risk of a malignant tumor on the side of the head where the cell phone is used.

The Swedish researchers acknowledge that the heightened risk was associated with heavy use of cell phones. By heavy use, it means use for a total of 2,000 or more hours, or about one hour per day for 10 years.

However, the FDA indicated that it would review all the studies as it had prepared to do so for some time. The FDA questioned the way the researchers conducted their study. It noted that the study used data collected through a mailed questionnaire coupled with a few follow-up phone interviews, but without in-person evaluations, suggesting the study is not reliable.

Two studies often cited in news reports that are contradictory to the current study are a Dutch Health Council review of worldwide research, which did not yield any association between brain tumor risk and use of cell phones, and a four-year British survey, which showed no link between use of cell phones, regardless of the duration of use, and the most common type of tumor.

There is no evidence of adverse effects associated with use of cell phones. But it concedes that if there is any risk, it is likely very small, the US FDA said.

Nevertheless, the US FDA indicated it "plans to convene a meeting in the near future to evaluate research conducted to date in this area and identify gaps in knowledge that warrant additional research," and it will continue monitoring studies for possible health problems from exposure to radiation.

The study, however, maintained that it considered a long term effect of wireless phone on the cancer risk in a larger population of subjects. Previous studies were relatively small and followed the subjects only for a shorter period. A cancer-causing effect may not manifest itself until 10, 20 or even more years later, meaning short term studies may not reveal the real risk of cell phone use.

The FDA responded to the study because it had received numerous queries following the news reports on the link of brain tumor with cell phone use.

Safety of wireless telephones

Wireless telephones are hand-held phones with built-in antennas, often called cell, mobile, or PCS phones. These phones are popular with callers because they can be carried easily from place to place.

Wireless telephones are two-way radios. When you talk into a wireless telephone, it picks up your voice and converts the sound to radio frequency energy (or radio waves). The radio waves travel through the air until they reach a receiver at a nearby base station. The base station then sends your call through the telephone network until it reaches the person you are calling.

When you receive a call on your wireless telephone, the message travels through the telephone network until it reaches a base station close to your wireless phone. Then the base station sends out radio waves that are detected by a receiver in your telephone, where the signals are changed back into the sound of a voice.

The Federal Communications Commission (FCC) and the Food and Drug Administration (FDA) each regulate wireless telephones. FCC ensures that all wireless phones sold in the United States follow safety guidelines that limit radiofrequency (RF) energy. FDA monitors the health effects of wireless telephones. Each agency has the authority to take action if a wireless phone produces hazardous levels of RF energy.

FDA derives its authority to regulate wireless telephones from the Radiation Control provisions of the Federal Food, Drug, and Cosmetic Act (originally enacted as the Radiation Control for Health and Safety Act of 1968).

FCC derives its authority to regulate wireless telephones from the National Environmental Policy Act of 1969 (NEPA) and the Telecommunications Act of 1996.