Last Call?

Nearly five decades ago, Americans learned that one of their most treasured habits—smoking—was lethal. This year, we could get more scary news, when scientists announce the results from Interphone, the largest-ever study to investigate whether cellphones cause cancer.

Interphone researchers are pooling and analyzing the results gathered from studies on 6,400 tumors sampled from patients in 13 countries. If the final results mirror the preliminary ones, the world's three billion cellphone users might want to dial back their talk time. Israeli researchers participating in Interphone found that people who use cellphones regularly are 50 percent more likely than non-users to develop brain tumors. And a joint Interphone analysis from the U.K., Denmark, Norway, Sweden and Finland reported a 40 percent increase in tumor risk in people who use cellphones for more than a decade; the study found no discernable risk for people who have used cellphones for fewer than 10 years.

No one yet knows specifically how cellphones could cause cancer. The radiation they emit has too little energy to cause genetic damage, but some scientists believe that it may have indirect effects that cause cells to proliferate uncontrollably. But there's no consensus on these theories.

Scientists like David Carpenter, the director of the Institute for Health and the Environment at the University of Albany, who spoke about cellphone risks at a Congressional subcommittee hearing in September, are looking to Interphone for a definitive ruling on cellphone safety but have expressed frustration over the two-years-delayed results.

An answer from Interphone is crucial for public health, Carpenter says. Although a handful of studies have been published on cellphones over the past few years, most have been statistically useless. For one thing, they surveyed too few people. Additionally, the majority of studies focused on the effects of cellphone use after several years, but in most cases brain cancer takes a decade to develop. Interphone looks at the influence of both short- and long-term use. That's not to say that the study is perfect. Interphone defines "regular" use as one call, once a week. It's possible that this definition underestimates the risk to people who use cellphones more frequently.

And what happens if Interphone reveals a definite link between cellphones and cancer? Will we find ourselves dependent on land lines again? Unlikely. The technology is probably here to stay, says Siegal Sadetzki, who ran the Israeli Interphone study: "We know that there are car accidents, and we still use vehicles, right? We've just learned how to do it wisely."

Read more of Popular Science's predictions for 2009.