We are exposed to radiation every day. This may seem alarming, but much of this radiation occurs naturally and is harmless in small doses. Knowing how much additional radiation exposure is caused by medical procedures, air travel, and other activities can help us make in formed decisions and avoid unnecessary worry.
The average person is exposed to approximately 6.2 millisieverts (mSv, the units used to measure the effective radiation dose) of radiation each year. This level of exposure is well below the international standards for radiation workers, which allow up to 50 mSv per year.
However, we should be aware of the hazards of excessive radiation exposure, especially since the effect of radiation is cumulative over a lifetime. Scientists estimate that for every 1,000 mSv of radiation that we receive, 0.2 mutations occur in our genes. Some of these mutations increase the risk for cancer, but not all mutations are dangerous—the average person already carries 50 gene mutations.
Natural radiation sources
Radiation is classified as ionizing (capable of freeing electrons from atoms or molecules) and non-ionizing. Ionizing radiation (e.g., x-rays) is considered more harmful than non-ionizing radiation (e.g., radio waves).
Most of the natural radiation that we receive is due to radon (a radioactive element) in the air. Airborne radon alone accounts for more than one-third (2.3 mSv) of the average person’s annual radiation exposure. Altitude also affects radiation exposure. For every additional foot above sea level, there is a minute increase in radiation per year due to cosmic radiation, or radiation from the sun and outer space.
Terrestrial (ground) radiation accounts for approximately 0.2 mSv (3.2%) of our annual exposure. What we consume also affects our exposure to radiation: food contains the radioactive isotopes carbon 14 and potassium 40, and some water contains additional radon. This, however, should not be a source of concern: together, food and water typically account for only 0.3 mSv (4.8%) of our annual radiation exposure.
Factors that increase radiation exposure
Although most radiation occurs naturally, environmental and lifestyle factors can increase our levels of exposure. Keep in mind that the amount each factor contributes to a person’s level of radiation exposure is usually very small.
Building materials contain varying levels of radon: living in concrete, stone, adobe, or brick buildings increases a person’s annual radiation exposure.
Air travel also exposes us to small amounts of radiation. Specifically, for every hour spent traveling by plane, a person is exposed to 0.005 mSv of ionizing radiation. The millimeter wave scanners at security checkpoints use non-ionizing radiation that is not known to be harmful.
Nearly half of the average person’s annual radiation exposure is due to medical testing, such as radiography (x-ray) and computed tomography (CT or CAT) scans. An average chest x-ray exposes the patient to around 0.1 mSv of radiation. CT scans, on the other hand, use multiple x-ray beams to form a three-dimensional image of the patient’s body. A patient receiving a chest CT scan receives around 7 mSv of radiation. Although radiography and CT scans expose patients to radiation and should not be overused, it is important to keep in mind the life-saving benefits of these imaging studies. Ultrasonography and magnetic resonance imaging do not use ionizing radiation.
An avoidable source of radiation is tobacco smoke. In addition to other carcinogens, tobacco smoke contains small amounts of the radioactive isotopes lead 210 and polonium 210.
Despite public concerns about cell phones, which use radiofrequency (non-ionizing) radiation, no relationship between cell phone use and cancer has been found. However, because data are not yet available from people who have used cell phones for several decades, the International Agency for Research on Cancer has classified radiofrequency radiation as a possible human carcinogen (cancer-causing agent).
Concerns and misconceptions
There is a common misconception that radiation exposure is one of the leading causes of cancer. This is largely due to well-publicized disasters such as chemical leaks, nuclear reactor meltdowns, and atomic bombings that greatly increased the cancer rates in surrounding areas. However, such disasters involve massive quantities of radiation (around 210 mSv, in the case of the bombing of Hiroshima) that are far above the typical annual exposure. In reality, radiation, when compared with certain chemicals and heavy metals, is one of the weaker cancer-causing sources.
While unnecessary radiation exposure should be avoided, we should keep the small risk of additional exposure in perspective. Medically necessary x-ray or CT scans should not be avoided because of radiation concerns, and patients should discuss any such concerns with their physicians.
— N. Danckers
For more information, talk to your physician or visit www.cdc.gov/nceh/radiation. To learn about radon, visit www.epa.gov/radon. To calculate your radiation exposure, visit www.ans.org/pi/resources/dosechart.
OncoLog, February 2015, Volume 60, Issue 2