With the proliferation of mobile devices and their extensive use, past studies on health risks related to cell phone radiation need to be re-examined, according to the U.S. Food and Drug Administration, which this week asked the National Research Council to identify further research that shows the effects of long-term exposure to these devices.

The council identified the need for studies of potential health outcome resulting from multiple, long-term, and low-intensity radio frequency exposure from mobile devices. Most current studies have been conducted to evaluate the effects of short-term exposure of healthy adults to radio frequency, according to the council.

More studies need to be conducted that measure the effects of extended mobile device use by teenagers, children, pregnant women, and fetuses, as well as exposure to cellular base station antennas. Although it's not yet known if children are more susceptible to radio frequency exposure, the research council and other medical and scientific institutions that make up the National Academies, believe children may be at increased risk because their organs are still developing. The National Academies provide science, technology, and health policy advice to Congress and the federal government.

It is believed that the current generation of children will be exposed to mobile devices for much longer periods than adults because they begin using the devices at an early age. A report issued by a National Academies committee cites several surveys that show a significant increase in children owning mobile devices. But there are no relevant studies that examine the health risks for children.

The council also suggests studies that analyze the amount of radio frequency energy produced by antennas in mobile devices and how it penetrates different parts of the body. There have been studies already conducted on the effects mobile device radiation has on the brain.

A study conducted in 2006 by the Swedish National Institute for Working Life found an increased risk of brain tumors in cell phone users. Past studies have also associated cell phones with cancer, although there are mixed views on the subject. Another report released in 2006 by British researchers says cell phones don't cause glioma, the most common type of brain tumor.

But mobile devices are now used in different ways than in the past. Newer phones, for example, have built-in antennas and with more people using them for texting and Internet access, the phones are held closer to other parts of the body, the report found.

Editor's Note: The headline was modified on Jan. 22 to refer to the correct government agency.