Radiophobia: Dental x-rays can kill you!–and other sage advice from the Land of Oz

A man freaks out about miniscule amounts of radiation from dental x-rays, declares on television to tens of millions of devoted viewers that a few routine radiographs can give people cancer, but he regularly crisscrosses the country and indeed the globe, thereby exposing himself to notably higher radiation doses in the form of cosmic rays.

This is not a false anecdote, but a real life scenario. It’s the case of Dr. Mehmet Oz. He’s been in the news a lot recently, trying to defend himself and his Columbia University faculty position against charges that the advice he gives out is based on pseudoscience. Most of the recent criticism has focused on his rants against chemicals and GMOs and his promotion of quack “natural” cures. But Oz cuts a wide swath. On his TV show, in 2010, he went on a rant against dental x-rays and mammograms.

Based partly on his reasoning that “the amount of radiation exposure, although it’s very small in mammography, it’s not that dissimilar from dental x-rays,” and partly on a thyroid cancer study conducted in Kuwait whose results he misconstrued, Oz reached the following conclusion: having more than five x-rays (dental films or mammograms) within a year would cause a fourfold increase in a person’s risk for thyroid medullary carcinoma. He then went on to recommend avoiding these types of X-ray scans—which should seem particularly odd, giving how Oz is a notorious jet setter.

To give all of his talks and promote his ideas in so many cities, Oz travels frequently through Earth’s skies, which means that his own annual exposure to ionizing radiation is many times higher than the levels of exposure that he has warned people to avoid.

Pilot’s dilemma?

This is not to say that Oz and others should avoid flying. On the contrary; even for a frequent flyer, the increased radiation exposure in the air compared with life on the ground is not a health concern. In aerospace medicine, there is concern about airline cabin crews having an elevated risk of cutaneous malignant melanoma (a deadly form of skin cancer) and breast cancer, but it’s not clear how much ionizing radiation from space contributes to the increased incidence. Some of the melanoma risk, at least, is do to increased exposure to non-ionizing ultraviolet radiation–not necessarily while flying.

Rather, because they travel a lot in their work and get free trips, pilots and flight attendants tend to vacation a lot in sunny, beachy places, and this could be the main reason for the increased melanoma incidence. Also, the disruption of the usual 24 hour day/night rhythm is thought to come into play, raising the risk for both melanoma and breast cancer. A few studies have suggested increased incidence of brain malignancy in pilots, which is speculated to result from heavy cosmic particles (nuclei of large atoms generated by explosions of distant stars), but the case on this issue is still open. What is not seen among pilots and other flight crew members, however, is an increase in thyroid malignancy and other cancers that typically are associated with exposure to high doses of beam radiation, such as X-rays. And, importantly, the radiation from a flat film X-ray scan should be even less of a concern.

Perspective on the relative radiation dose

In high doses, ionizing radiation (particle or electromagnetic wave energy concentrated enough to strip electrons from atoms) is one of the worst dangers the universe has to offer. As dramatized in medical detail in the 1989 film Fat Man and Little Boy, which tells the story of the Manhattan Project, very high doses of ionizing radiation produce what’s now called acute radiation sickness, which can kill rapidly. Thousands of victims of the Hiroshima and Nagasaki bombs who were close to ground zero, but not close enough to be killed instantly by the blast, died within a few days. Further out from the blast sites, and also around the Chernobyl nuclear accident of 1986, there were major increases in the rates of various cancers, especially leukemia and thyroid cancer. Either way, it’s a horrible way to die, and everybody is aware of this, so it is quite understandable why the word “radiation” provokes fear.

But the quantity and duration of exposure really matters. At low doses, ionizing radiation probably is not much of a health issue at all, and it’s quite possible that low dose radiation could be good for you. Radiation is natural. We–all life on Earth–grew up with it. At this moment, high energy particles from space are passing through your body, penetrating your cells, causing errors in your DNA. But there’s nothing to worry about. Over billions of years, our cells have evolved repair mechanisms to correct the damage, so the genetic errors do not persist.

In most North American cities, people receive background ionizing radiation at a dose of approximately 3 mSv per year. That’s due to radon in the air, radioactive isotopes in the ground, and cosmic radiation and solar particles coming from space. As you ascend, the contribution from space radiation increases, so high altitude places have higher levels of natural background radiation.

How does this compare with the kind of diagnostic X-ray scans that concern Dr. Oz?

To answer this, first of all, it should be noted that Oz was not even correct in his assumption that, “[the amount of radiation exposure in mammography is] not that dissimilar from dental X-rays”. Mammography imparts a radiation dose of approximately 0.4 mSv, but a dental x-ray usually is a lot lower, typically around 0.005 mSv.

That means you’d need about 80 dental films to get the same amount of radiation as you get from a mammogram. By ignoring the numbers, Oz started off the radiation discussion on the wrong foot, and it got worse. It also means that you need seven mammograms, or 600 dental films, in a year just to double your usual yearly exposure to ionizing radiation. And doubling your normal exposure is not a big deal. Much easier than getting 600 dental films, you could double your exposure simply by moving from a sea level city to Santa Fe, New Mexico, or some other high altitude locale.

In terms of X-ray dose, intermediate between a dental X-ray and a mammogram, a flat film chest X-ray typically gives you a dose of about 0.1 mSv, and in real-life medicine, none of these doses is of the level that worries clinicians and public health officials. Instead, people who actually study radiation are worried about increased cancer risk from diagnostic procedures such as full body computed tomography (CT). One full-body CT scan gives you about 12 mSv, meaning about 100 chest films worth, 25 mammograms worth, or 2,400 dental films worth of X-radiation.

Based on analysis of cancer following the Japanese atomic bombings and Chernobyl and various epidemiological studies in health settings, there are enough data for researchers to be concerned that one’s risk of developing fatal cancer may rise with exposure to radiation on the order of a full-body CT dose. However, even in this case, the calculated increased risk is only slight, meaning that it increases by one case per several thousand people.

Flying and radiation

The dose of radiation that you get on any flight in a given amount of time varies, depending on altitude, latitude and various other factors. Flying over the continental US, typically you receive 1-2 dental X-rays worth of radiation each hour, and thus in a story by NPR, it is stated that flying from New York to LA, you get roughly the equivalent of 8 dental X-rays. Flying across the Atlantic to Europe, typically the exposure is higher, because you fly closer to the North Pole, where the levels of cosmic radiation are much higher compared with areas close to the Equator.

For this reason, sometimes you hear the radiation dose for these flights explained in terms of how many chest X-rays worth of radiation you get. Still, it’s not a lot, if you keep that full body CT perspective in mind. That CT dosage, 12 mSv, may sound high based on what we’ve discussed so far, but for perspective consider that during a 2-3 year mission to Mars it’s predicted that astronauts could receive a full Sievert of space radiation. That’s cumulative over the entire mission, but it would be like getting more than 80 full-body CT scans during that amount of time on Earth. It’s up to you to figure out how many dental X-rays you’d need to equal that.

Low dose radiation: Are effects really cumulative?

By the time that astronauts go to Mars, we may have better radiation protection technology than exists today. We also probably will have advanced nuclear propulsion, which would reduce the cumulative radiation exposure by transporting the astronauts much more quickly between Earth and Mars than is possible with chemical propulsion. Instead of nearly a year of travel time, for instance, certain nuclear propulsion systems now in the research stages could reduce the time to one month in each direction. Because astronauts would receive much more radiation from the space environment than from a well-designed nuclear reactor, nuclear energy would reduce the radiation exposure to a fraction of what it would be otherwise. It would also make a Mars mission much safer for several other reasons not related to radiation, also due to the reduced travel time.

Even without improved propulsion and radiation protection technology, however, it’s important to note that a large radiation dose spread out over time is not the same thing as getting the dose all in one burst. We evolved in an environment that provides constant low level radiation and our cells are good at dealing with it. Going back decades to the time when the health effects of radiation were first observed, there has always been a question of whether there is a threshold of radiation exposure, an exposure dose below which you are not damaged in any way. In other words, if the usual 3 mSv per year does not harm us, how much above that can we go with no ill effects? If we can get exposed up to a certain level continuously with no harm, then logically, there is no reason to add up all of the little exposures into into an annual, cumulative dose to assess one’s cancer risk. Why then, do we constantly hear about how much radiation is dangerous, or not dangerous, per year?

The reason is that currently clinical medicine and public heath operate on the assumption that there is no threshold at all. In radiation health science, there is a mathematical concept called the linear no-threshold model. Based on information from populations exposed to varying medium to high levels of radiation, especially during the two atomic bomb blasts in Japan at the end of World War II, the rates of various cancers have been calculated in comparison with the radiation dose. The higher the dose, the more leukemia and the more thyroid cancer and you can draw a line showing that more people got sick in places close to the bomb blast, where radiation was at a very high level, compared with places a little further out, where radiation levels were not quite as high. We’re not talking about chest X-ray doses, however, or CT scan doses, but higher levels. Getting exposed to say, 1/30th, 1/20th or 1/10th of the Mars mission dose, not over a long space mission, but instantly when the bomb exploded, absolutely gave people cancer. The higher the dose, the more cancer cases there were until the dose was so high that people didn’t live long enough to get cancer and died instead from acute radiation sickness. But there were no data on low level radiation. Thus, to make an estimate on what kind of risk you’d get from low doses, the line plot from the medium to high doses was extrapolated backward.

Since the mid twentieth century, when atomic bomb cancer cases were first analyzed epidemiologically, scientists have been applying this back extrapolation technique over an over. The line is extended backward to calculate risks for cancer from very low levels of radiation–in other words, if a lot of radiation causes a lot of cancer, then a little radiation causes a little cancer. What do we mean by “a little cancer”? It means that on the part of the line corresponding to tiny radiation exposures–that part of the line that was drawn by backward extrapolation, not based on actual low dose data–the calculated increased risk ends up being lower than 1 case in 100,000 people.

But, importantly, that one case in hundreds of thousands of people develops from low dose radiation, only if there is no threshold, meaning if there is no minimum exposure below which the radiation doesn’t harm you. That’s the linear no-threshold model, and it’s used as a guideline for radiation exposure, to be on the safe side, but not because there’s any evidence of its validity.

Drawbacks of the linear no-threshold model

The problem with this model is that it may not be correct, and by employing it just to be on the safe side, we end up telling everyone to watch out, even for small potential exposures to radiation. As a society, we play it particularly safe, when it comes to pregnancy. Epidemiologically, we know that a dental X-ray, a chest X-ray even a pelvic X-ray is not going to harm a fetus, but pregnant women are conditioned to avoid those tests, though strangely not flying, which exposes the fetus to higher doses. If the thought of radiation from a dental X-ray gives people the same feeling that they get from the thought of radiation from a Mars mission, then any fear is completely irrational, and it makes sense to call the phenomenon “radiophobia”.

If we are a radiophobic society, it’s probably safe to say that the aversion that many people have to nuclear energy is not based on a rational concern about nuclear accidents–in the US, nuclear power plants are actually very well safeguarded against this–but on a fear of any radiation at any level. Only when people develop a realistic grasp of what’s a lot of radiation vs. what’s negligible can we have a useful public discussion in this country about the benefits and drawbacks of nuclear power.

Even beyond the possible existence of thresholds for safe radiation exposure, there has been growing evidence over the last few decades that low level radiation could have some positive effects on human cells. The idea, something that I covered recently for Discover Magazine, is called radiation hormesis. Essentially, it’s the opposite of the linear no-threshold model and it means that low doses of ionizing radiation can be helpful by stimulating DNA repair and other normal functions in our cells. Radiation hormesis is hotly debated, but a string of studies on laboratory animals have brought it to the forefront, and if it proves correct it will mean that avoidance of low dose radiation might actually be harmful to health. But even bringing up the topic of radiation hormesis could be pretty hard for mainstream media, if indeed we live in a society that suffers from radiophobia. And at the moment, fear of anything related to radiation does seem to be  widespread. Take, for example, the topic of food irradiation.

Food irradiation

Just surfing through various naturopathic websites, such as The Nature Guide, you’re inundated with articles written to reach beyond the usual anti-GMO and organic-only consumers, to a public that fears radiation based on lack of information about it. Thus, when taking about irradiation of food, one article opens like this:

The radiation may come from nuclear material such as cobalt 60 or cesium 137 (both highly toxic), from x-rays or electronic beams. Usually, 100,000 RADS is administered to meats, vegetables and fruits, and up to 3,000,000 RADS is administered to spices.[i] Supposedly, the food doesn’t become radioactive, but other biochemical changes do occur…

We can stop at the word “supposedly”, as it shows how far the writer is willing to go. Of course, the food does not become radioactive by having X-rays or electrons shot through it. The most elementary high school physics course would provide enough of an explanation as to why not, but including “supposedly” sends a subtle message to the reader that maybe the physicists could be wrong. Then, the part about biochemical changes in the food–which is not a lie, but a misrepresentation of facts–seems like a side issue to the reader.

Food irradiation actually has been found to be safe by the FDA, and it has some great benefits. In particular, by keeping food safe of potential deadly microbial strains, such as E. coli, food irradiation can save lives. As far as biochemical changes in the food with irradiation, it’s true that radiation breaks up chemical bonds, causing rearrangements that alter chemical compounds, but so does cooking, and so do a lot of other processes to which food is subject. The bottom line is that the FDA has found food irradiation to be safe, based on a wealth of research. As with diagnostic X-rays, the only reason to fear it is having an irrational fear, namely radiophobia.

David Warmflash is an astrobiologist, physician, and science writer. Follow @CosmicEvolution to read what he is saying on Twitter.

3 thoughts on “Radiophobia: Dental x-rays can kill you!–and other sage advice from the Land of Oz”

  1. So I presume Oz doesn’t eat either gmos (we knew that) OR organic foods produced by mutagenesis (chemical and/or irradiation altered seeds).

    Reply
  2. Interestingly, the official recommendation of the American Dental Association says:

    Dentists should not prescribe routine dental radiographs at preset intervals (ie, every 6 months, every year) for all patients [1].

    While [2,3] concluded that:

    As with all sources of artificial ionizing radiation, considered use of this modifiable risk factor may be of benefit to patients [2].

    Accordingly, dentists should select patients wisely—only take X-rays when there is patient-specific reason to believe there is a reasonable expectation the X-rays will offer unique information influencing diagnosis or treatment [3].

    Finally, doctors are estimated to cause around 29 000 cancers yearly in the US by dosing patients with x-rays during CT scans [4].
    CT scans are estimated to cause 29 000 cancers

    Just some science to think about.

    [1] Council on Scientific Affairs. American Dental Association, US Department of Health and Human Services, Food and Drug Administration. Dental radiographic examinations: Recommendations for patient selection and limiting radiation exposure. 2012. Available at: http://www.ada.org/sections/professionalResources/pdfs /Dental_Radiographic_Examinations_2012.pdf. Accessed March 4, 2013.
    [2] Claus, Elizabeth B., et al. “Dental x‐rays and risk of meningioma.” Cancer 118.18 (2012): 4530-4537.
    [3] White, S. C., and S. M. Mallya. “Update on the biological effects of ionizing radiation, relative dose factors and radiation hygiene.” Australian dental journal 57.s1 (2012): 2-8.
    [4] Schmidt, Charles W. “CT scans: balancing health risks and medical benefits.” Environmental health perspectives 120.3 (2012): a118.

    Reply
  3. Conflicting information everywhere, and most of the people arguing that dental x-rays are safe are either dentists or others using no data. Physicists have found that even very low doses are dangerous. X-rays don’t make it to the ground because of the atmosphere. Dentists lie to us when they say we “get more radiation” from walking in the sun, because that’s UV rays, not x rays. X rays are almost gamma rays, and both tear apart DNA because they knock electrons out of orbit. [acting more like a particle than a wave] Furthermore, a concentrated beam, man made, is something humans are not evolved to handle. If one side of the helix breaks, it is repairable. The DNA repairs itself. If BOTH sides break (a double break) that is where the real damage is done, and mutations will take place. No one can assume that a dental x-ray doesn’t do any double breaks. Every dentist I’ve been to has demanded x-rays even when totally not necessary, even when they’ve been done already, and it’s a money making scam, disregarding the risks to people to make money. They were adamant about Mercury fillings being safe for decades. Now they don’t do them anymore. It’s proven they aren’t safe. They never admit that they are wrong until litigation and repeated years of research prove them wrong and make them pay. That’s when.

    Reply

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