X-Rays, sunshine: Could radiation be hurting your health?

When Sheri Diehl, a Chicago-area flight attendant, got -- and finally stayed --pregnant after four miscarriages in the 1990s, she contacted her supervisor and asked to stop flying immediately. Her biggest worry? Radiation. She knew the airplane's shell didn't protect her from the sun's rays at high altitude. Diehl and her fellow flight attendants had long wondered -- Could there be unknown health risks for frequent fliers? -- which now included her baby. "I wasn't taking any chances," she says.

Radiation exposure is on the rise, thanks largely to the popularity of high-tech medical exams such as CT scans.

Diehl's baby was fine. But her worries were more than new-mom-to-be jitters. We're all exposed to radiation sources -- the sun, X-rays, mammograms, CT scans, dental exams, even soil -- and we're just now finding out whether those rays, combined, are dangerous.

So how much radiation is too much? Scientists are still figuring that out-- and they tend to disagree about the risks. But they recently found worrying signs that radiation exposure is on the rise, thanks largely to the popularity of high-tech medical exams such as CT scans. So it's wise to follow in Diehl's footsteps and be smart about limiting exposure. Here's what you need to know.

Why radiation is scary

The odds of developing cancer from radiation exposure are very small, but risks do rise the more you get zapped and the younger you are when you're radiated, according to the National Academy of Sciences. This means putting off radiating medical scans, if they're not medically necessary, is always good for you because radiation can damage cell DNA-- and that damage can lead to cancer years down the road. It's true that your body can repair the damage or the cell may simply die. But the earlier you get radiated, the more opportunity there is for uncorrected errors to start cropping up in your DNA.

Know your radiation footprint

To understand what's typical and how radiation adds up, remember this number: 3 mSv. (mSv stands for millisievert, the scientific unit of measurement for radiation.) That's how much radiation, on average, a person in the United States absorbs in a year from background sources such as sunlight, soil, and radon gas that may be in our homes or offices. "If you add the man-made sources like radiation from smoke detectors or X-rays it rises to an average of about 3.6 mSv," says Cynthia McCollough, Ph.D., a radiation-dose researcher at the Mayo Clinic in Rochester, Minnesota. That's not much, but your footprint gets bigger fast if you have multiple radiation-based medical tests.

Learn the limits

Health.com: Estimate your annual radiation dose with this chart. Then remember that while some scientists don't believe any level of radiation is necessarily safe, the International Commission on Radiological Protection says that the maximum acceptable dose depends on the source and the purpose. For the general public, it's about what you get from background radiation -- 3 mSv per year. But if you need a medical exam (or several exams), the acceptable limit is as high as 20 mSv per year.

Weigh the risks

At some time in your life, of course, you'll need a radiation-based medical treatment or diagnostic test. Radiation therapy may be the best way to shrink a cancer or save a life. But you should weigh each diagnostic test carefully, experts say. For instance, studies show that having a mammogram from age 40 and up saves lives. "Most often the benefits of such tests and treatments outweigh the risks," says Henry Royal, M.D., a professor of radiology at Washington University in St. Louis, MIssouri. But getting a mammogram before age 40 or having more than one per year carries higher risks and should be avoided unless your personal risk factors are high. The same goes for DEXA scans, a low-radiation scan for evaluating bone density and catching signs of osteoporosis. Like mammograms, the earlier you start DEXA-scan screenings, the more radiation you'll absorb over your lifetime. That's one reason the U.S. Preventive Services Task Force, a standards-setting body, uses age 65 as the starting point for DEXA scans, unless there's a history of bone fractures or high risk of osteoporosis. Health.com: What is radiation therapy?

If you break your ankle on vacation, an X-ray can't be avoided. But you can ask for copies of the X-ray so that you don't need a second one when you get home. And do you really need dental X-rays every six months to look for hidden cavities? If your teeth are generally healthy and you brush and floss regularly, ask your dentist about annual or biannual bitewing X-rays instead.

Avoid the CT scan bandwagon

A recent study in The New England Journal of Medicine warned that up to one-third of all CT scans may be medically unnecessary -- and that 20 million Americans may be radiated unnecessarily every year. With some 65 million CTs performed annually in the United States, study authors David Brenner, Ph.D., and Eric Hall, Ph.D., of Columbia University Medical Center in New York City suggested that up to 2 percent of all future cancers may be caused by radiation from CTs. Health.com: What's a CT scan?

While your odds of cancer from one CT scan are minuscule -- 1 in 2,000 -- the study also reported that some scans may be riskier than others. A typical, full-body CT scan (often used in emergency rooms to check for internal injuries after car accidents) can emit 200 to 250 times as much radiation as a chest X-ray. The same numbers apply to full-body scans at boutique medicine storefronts designed for healthy people wondering if they have undiscovered diseases.

There is no doubt that CTs can be incredibly useful, but some experts believe that doctors may order full-body CTs to protect themselves from possible malpractice suits following emergencies, on the off chance that they'll miss something. Always ask whether a CT scan is absolutely necessary, says William McBride, Ph.D., a radiation-oncology expert at the University of California, Los Angeles, Jonsson Cancer Center. Health.com: I paid $450 to boost my cancer risk

Rethink those frequent flier miles

Frequent flying theoretically ups your cancer risks. After all, seven miles above sea level, there's much less atmosphere to absorb radiation from the sun. The Association of Flight Attendants takes the risk seriously enough that it recently warned members (who fly an average 100,000 to 450,000 miles a year) that some researchers have found "a significant increased risk of breast cancer among female flight attendants."
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