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A Simple Step to Reduce DNA Damage from CTs and X-rays

Author: Jian Gao, PhD

Editor: Mr. Frederick Malphurs

November 21, 2023

The Damage Is Real

Medical imaging has revolutionized diagnosis – offering unprecedented clarity in detecting internal abnormalities such as injuries and cancer. Despite its enormous benefits, medical imaging is not without risks – radiation from medical imaging such as CT scans and X-rays can damage DNA which could lead to cancer. Children are particularly vulnerable to radiation exposure. A large Australian study published in the prestigious BMJ (British Medical Journal), which analyzed 10.9 million children 19 years or younger, found the overall cancer incidence was 24% greater for those exposed to CT scans than for those unexposed. And the study found a dose-response relationship – the larger the dose of radiation, the higher cancer risk.1

Another large study from the UK is even more unsettling. The study published in Lancet, one of the world’s top medical journals, found “Compared with patients who received a dose of less than 5 mGy, the relative risk of leukemia for patients who received a cumulative dose of at least 30 mGy (mean dose 51.13 mGy) was 3.18 and the relative risk of brain cancer for patients who received a cumulative dose of 50-74 mGy (mean dose 60.42 mGy) was 2.82.” In other words, those younger than 22 who had two or more CT scans (an average radiation dose per scan is about 15 mGy or mSv) increased their risks of leukemia and brain cancer by 318% and 282%, respectively.2

Bear in mind, these are epidemiological studies based on real data rather than extrapolated from theoretical models – the findings are real. Nevertheless, please do not be scared away from CT scans when really needed. As scary as these findings are, they are relative risks, not absolute risks (the number of individuals getting cancer) which are much smaller. For starters, the relative risk is calculated as the ratio of cancer risk of the exposure group to the risk of the non-exposure group. For example, if three cancer cases occurred among 1,000 patients exposed to repeated CT scans and only one case occurred in 1,000 patients not exposed, the relative risk is 3 or 300%. But the absolute risk is only 0.2% = (3 – 1)/1000.

Both relative and absolute risks are informative. Many studies only report the relative risks, but others also report the absolute risks. For instance, a 2007 study published in the New England Journal of Medicine found CT scans contributed to 1.5-2% of all cancer cases,3 which means 30,000-40,000 more cancer cases in 2023 due to CT scans. This is very likely an underestimate because the number of CT scans in the US was about 6.2 million in 2007 while it is over 8 million in 2023.

WebMD describes the cancer risk from CT scans this way: “Overall, your odds are very low – the chance of getting a fatal cancer from any one CT scan is about 1 in 2,000.”4 However, given over 80 million CT scans performed annually, 1 in 2,000 is tantamount to 40,000 new cancer cases due to CT scans. 

Considering another study published in JAMA Internal Medicine estimated 29,000 new cancer cases related to CT scans in 2007,5 the estimate of 30,000-40,000 new cancer cases in 2023 due to CT scans appears to be rather conservative.

Among all the imaging techniques, the radiation effects of CT scans have been studied most because (1) the number of CT scans has increased 27-fold in the last 43 years from about 3 million in 1980 to over 80 million today, and (2) CT scans emit much large radiation doses as shown in the Table below.3 A single CT scan emits up to 2,000 times the radiation of a conventional x-ray. “Many studies have shown that organ doses associated with routine diagnostic CT scans are similar to the low-dose range of radiation received by atomic-bomb survivors.”6

As shown in the Table above, although the radiation dose from mammograms is not as large as that of CTs, it is not totally benign either. Studies have found mammograms can induce breast cancer albeit the odds are small.7-11 For instance, a study published in the Annals of Internal Medicine concluded “On average, annual screening of 100,000 women aged 40 to 74 years was projected to induce 125 breast cancers leading to 16 deaths relative to 968 breast cancer deaths averted by early detection from screening.”12

The benefit of mammograms is obvious, but the risk of radiation-induced breast cancer should not be ignored.

Vitamin C Can Save the Day

Not all is lost. Numerous studies have consistently demonstrated vitamin C supplementation prevents DNA damage from radiation exposure,13-20 and repairs DNA damage induced by radiation.21 In addition to the ‘traditional’ radicals created by radiation, vitamin C can counteract radiation-induced long-lived radicals (LLRs) that destabilize chromosomes and induce cancerous DNA mutations.22 Furthermore, vitamin C is also shown to inhibit radiation-induced death of human blood cells.23 Moreover, vitamin C has also been shown to reduce DNA damage caused by UV rays (UVA and UVB) from the sun.24,25 These findings are not surprising because vitamin C is arguably the most well-known and strongest antioxidant scavenging and neutralizing free radicals by donating electrons to them (free radicals have unpaired electrons and tend to steal electrons from other molecules like DNA and alter their fundamental structure and functions).

In a lab study where 40 mice exposed to a lethal dose of radiation were randomly assigned to four groups – three treatment groups received vitamin C equivalent of 200, 400, 800 mg per kilogram body weight daily for five days, and the control group received no treatment. At the end of the study the survival rate in the control group was 50% while the survival rates of all three treatment groups were 90%.26             

Given the significance of these findings, this study should have been refined to find out the minimum vitamin C dosage needed to reach the 90% survival rate – it is very likely that less than 200 mg/kg is needed since the survival rate with 200mg/kg is not lower than the survival rate of 400 and 800 mg/kg. By human standards, a dose of 200 mg/kg body weight is quite high, equivalent to 20 grams for a 220-pound person. Disappointingly, no further studies to refine the results have appeared yet – probably that is because nobody can make money out of vitamin C preventing cancer.

Nevertheless, dosages for animals are hardly relevant to humans. Luckily, there are a few studies on humans offering us some guidance. For instance, a 2019 study published in the European Journal of Radiology assessed the protective effect of vitamin C by studying 60 patients undergoing abdominal multiphase contrast-enhanced CT scans. The researchers divided the 60 patients into a prevention group (n = 30) and control group (n = 30). Patients in the prevention group were orally administered 1 g vitamin C at 30, 60, or 120 minutes prior to the CT examination, but no treatment was given to the control group. The DNA damage (measured by the γ-h2ax assay) was measured immediately after the CT scan.

The study found the mean increase in γ-H2AX was 0.49 foci/cell in the control group while it was only 0.19 foci/cell in the prevention group (p < 0.001). In other words, one gram of vitamin C intake reduced 61% of DNA damage caused by CT scans. According to the study, the vitamin C administration time (30, 60, and 120 minutes prior to CT examination) did not make any difference in preventing DNA damage.27

In a similar randomized controlled trial published in the Journal of the American College of Cardiology, researchers from Switzerland studied patients exposed to radiation from X-ray–based cardiac examinations. The study found the DNA damage was reduced by 87% among the individuals who received intravenous infusion of vitamin C (3 grams) compared to those in the control group (infused with saline). The study also tested NAC (N-acetyl cysteine, a popular dietary supplement as an antioxidant) and found it reduced DNA damage by 43%.28   

Evidently, studies have consistently demonstrated vitamin C intake before x-ray-based examinations can substantially reduce radiation-induced DNA damage. Yet, no government agencies or professional societies have come out to endorse vitamin C for preventing DNA damage from radiation, let alone establish guidelines. Consequently, there is no official recommendation on how much vitamin C to take and when to take it.

Based on existing studies, it appears to be rational to take 1-3 grams of vitamin C depending on the body weight an hour before CT scans or other X-ray-based examinations. Other antioxidants like vitamins A and E have also been shown to be effective,29 but vitamin C has some advantages: effective, inexpensive, readily available, and most importantly, safe; it is safer than water – drinking too much water can kill, but nobody can get killed by taking too much vitamin C.

Despite all the benefits, the decision to take vitamin C to reduce DNA damage is tricky for those undergoing cancer radiation therapy. Although a study showed vitamin C supplementation improved a key biomarker (neutrophil-lymphocyte ratio) associated with mortality,30 there is a concern that vitamin C supplementation may not only protect normal but also cancer cells from radiation.31 More research is needed in this area.

Avoid Unnecessary Exposure

Nevertheless, vitamin C cannot prevent all the DNA damage caused by CT scans. It is important to ask your radiologist or technician about radiation dose before the CT scan – probably it is better to inquire at the time the appointment is made. Studies have shown the radiation dose can be significantly lowered without compromising the quality of the pictures.32,33 CT machines have several parameters your radiologist can adjust to optimize the radiation dose. You need to ask about the radiation dose because a study shows only 47% of radiologists and 9% of emergency department clinicians are aware that the doses of radiation are associated with development of cancer, and only 7% of the patients are informed of the risks of their CT scan.34 More importantly, you need to make sure you do not get more radiation than you need accidentally due to a technician’s mistake. It happens.35

In addition, the use of a contrast agent during CT scans to enhance the quality of the pictures can significantly increase radiation doses – up to 30%.36,37 Ask your doctor if the contrast is really needed. Above all, ask your doctor if you really need a CT scan, or if an alternative such as MRI can be used. Studies found 20-40% of CT scans were not necessary and should not have been ordered.38

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Taken together, DNA damage from CT scans and other X-ray-based examinations is real. Given the gravity of potential DNA damage, the radiation dose should be by law written in the physicians’ orders and communicated to patients just like the dosage of a medication in the prescription. And a digital display of the radiation level on CT or X-ray machines at the time of examinations should be required too.

Be Real

For variety of reasons, it is unlikely to see transparency on radiation doses from x-ray-based examinations like CT scans anytime soon. The good news is that the protective effect of vitamin C is proven – the evidence cited in this article is based on real data rather than theoretical models.

For starters, there are mainly three competing theoretical models about the relationship between radiation dose and DNA damage:39-41 one is called linear-no-threshold (LNT) model assuming any amount of radiation causes DNA damage in proportion to the dose received. The other one is referred to as linear-quadratic (LQ) model postulating the LNT model is applicable only when the dose is small, but as the dose increases, the DNA damage accelerates exponentially. The third one is called threshold-quadratic (TQ) model hypothesizing no DNA damage would occur until the exposure reaches a threshold (cumulative doses of 100 mSv), above which the DNA damage increases exponentially. Apart from these three models, a novel theory known as the hormesis model suggests that small-dose radiation may be beneficial. Go figure.  

Regardless of how the theorists spin their models, again, the research findings cited in this article are based on real data, not theoretical models. For those who need multiple CT scans, especially for young children who are more susceptible to radiation, it is better to be safe than sorry – press for the radiation dose you will receive and take vitamin C before any CT scan or other X-ray-based examinations.  

About the Author and Editor: Jian Gao, PhD, is a healthcare analyst/researcher for the last 25 years who devoted his analytical skills to understanding health sciences and clinical evidence. Mr. Frederick Malphurs is a retired senior healthcare executive in charge of multiple hospitals for decades who dedicated his entire 37 years’ career to improving patient care. Neither of us takes pleasure in criticizing any individuals, groups, or organizations for the failed state of healthcare, but we share a common passion — to reduce unnecessary sufferings inflicted by the so-called chronic or incurable diseases on patients and their loved ones by analyzing and sharing information on root causes, effective treatments, and prevention.

Disclaimer: This article and any contents on this website are informational or educational only and should by no means be considered as a substitute for the advice of a qualified medical professional. It is the patients and caregivers’ solemn responsibility to work with qualified professionals to develop the best treatment plan. The author and editor assume no liability of any outcomes from any treatments or interventions.

References

  1. Mathews JD, Forsythe AV, Brady Z, et al. Cancer risk in 680,000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians. BMJ. 2013 May 21;346:f2360. doi: 10.1136/bmj.f2360. PMID: 23694687; PMCID: PMC3660619.
  2. Pearce MS, Salotti JA, Little MP, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet. 2012 Aug 4;380(9840):499-505.
  3. Brenner DJ, Hall EJ. Computed tomography–an increasing source of radiation exposure. N Engl J Med. 2007 Nov 29;357(22):2277-84.
  4. https://www.webmd.com/cancer/can-ct-scans-lead-to-cancer
  5. Berrington de Gonzalez A, Mahesh M, Kim KP, et al. Projected cancer risks from computed tomographic scans performed in the United States in 2007. Arch Intern Med. 2009 Dec 14;169(22):2071-7.
  6. Semelka RC, Armao DM, Elias J Jr, Huda W. Imaging strategies to reduce the risk of radiation in CT studies, including selective substitution with MRI. J Magn Reson Imaging. 2007 May;25(5):900-9.
  7. Hauge IH, Pedersen K, Olerud HM, et al. The risk of radiation-induced breast cancers due to biennial mammographic screening in women aged 50-69 years is minimal. Acta Radiol. 2014 Dec;55(10):1174-9.
  8. Yaffe MJ, Mainprize JG. Risk of radiation-induced breast cancer from mammographic screening. Radiology. 2011 Jan;258(1):98-105.
  9. Eidemüller M, Holmberg E, Lundell M, Karlsson P. Evidence for Increased Susceptibility to Breast Cancer from Exposure to Ionizing Radiation Due to a Familial History of Breast Cancer: Results From the Swedish Hemangioma Cohort. Am J Epidemiol. 2021 Jan 4;190(1):76-84.
  10. Ronckers CM, Erdmann CA, Land CE. Radiation and breast cancer: a review of current evidence. Breast Cancer Res. 2005;7(1):21–32.
  11. Løberg M, Lousdal ML, Bretthauer M, Kalager M. Benefits and harms of mammography screening. Breast Cancer Res. 2015 May 1;17(1):63. doi: 10.1186/s13058-015-0525-z.
  12. Miglioretti DL, Lange J, van den Broek JJ, et al. Radiation-Induced Breast Cancer Incidence and Mortality from Digital Mammography Screening: A Modeling Study. Ann Intern Med. 2016 Feb 16;164(4):205-14.
  13. Konopacka M, Rzeszowska-Wolny J. Antioxidant vitamins C, E and beta-carotene reduce DNA damage before as well as after gamma-ray irradiation of human lymphocytes in vitro. Mutat Res. 2001 Apr 5;491(1-2):1-7.
  14. Kanter M, Akpolat M. Vitamin C protects against ionizing radiation damage to goblet cells of the ileum in rats. Acta Histochem. 2008;110(6):481-90.
  15. Naeeji A, Mozdarani H, Shabestani Monfared A, et al. Oral Administration of Vitamin C, Cimetidine and Famotidine on Micronuclei Induced by Low Dose Radiation in Mouse Bone Marrow Cells. J Biomed Phys Eng. 2017 Jun 1;7(2):117-126.
  16. Konopacka M, Widel M, Rzeszowska-Wolny J. Modifying effect of vitamins C, E and beta-carotene against gamma-ray-induced DNA damage in mouse cells. Mutat Res. 1998 Sep 11;417(2-3):85-94.
  17. Al Alani EA, Al Musawi MS, Mahdi AH. Influence of vitamin C on irradiated mice tissues induced DNA double strand breaks DSB using gH2AX marker. J Pak Med Assoc. 2021 Dec;71(Suppl 8)(12):S117-S122.
  18. Brabson JP, Leesang T, Mohammad S, Cimmino L. Epigenetic Regulation of Genomic Stability by Vitamin C. Front Genet. 2021 May 4;12:675780. doi: 10.3389/fgene.2021.675780.
  19. Sram RJ, Binkova B, Rossner P Jr. Vitamin C for DNA damage prevention. Mutat Res. 2012 May 1;733(1-2):39-49.
  20. Smith TA, Kirkpatrick DR, Smith S, et al. Radioprotective agents to prevent cellular damage due to ionizing radiation. J Transl Med. 2017 Nov 9;15(1):232. doi: 10.1186/s12967-017-1338-x. PMID: 29121966; PMCID: PMC5680756.
  21. Konopacka M, Palyvoda O, Rzeszowska-Wolny J. Inhibitory effect of ascorbic acid post-treatment on radiation-induced chromosomal damage in human lymphocytes in vitro. Teratog Carcinog Mutagen. 2002;22(6):443-50.
  22. Waldren CA, Vannais DB, Ueno AM. A role for long-lived radicals (LLR) in radiation-induced mutation and persistent chromosomal instability: counteraction by ascorbate and RibCys but not DMSO. Mutat Res. 2004 Jul 13;551(1-2):255-65.
  23. Witenberg B, Kletter Y, Kalir HH, et al. Ascorbic acid inhibits apoptosis induced by X irradiation in HL60 myeloid leukemia cells. Radiat Res. 1999 Nov;152(5):468-78.
  24. Kawashima S, Funakoshi T, Sato Y, et al. Protective effect of pre- and post-vitamin C treatments on UVB-irradiation-induced skin damage. Sci Rep. 2018 Nov 1;8(1):16199. doi: 10.1038/s41598-018-34530-4. PMID: 30385817; PMCID: PMC6212420.
  25. Besaratinia A, Kim SI, Bates SE, Pfeifer GP. Riboflavin activated by ultraviolet A1 irradiation induces oxidative DNA damage-mediated mutations inhibited by vitamin C. Proc Natl Acad Sci U S A. 2007 Apr 3;104(14):5953-8.
  26. Mortazavi SM, Rahimi S, Mosleh-Shirazi MA, et al. A Comparative Study on the Life-Saving Radioprotective Effects of Vitamins A, E, C and Over-the-Counter Multivitamins. J Biomed Phys Eng. 2015 Jun 1;5(2):59-66.
  27. Tao SM, Zhou F, Joseph Schoepf U, et al. The effect of prophylactic oral vitamin C use on DNA double-strand breaks after abdominal contrast-enhanced CT: A preliminary study. Eur J Radiol. 2019 Aug;117:69-74.
  28. Stehli J, Fuchs TA, Ghadri JR, et al. Antioxidants prevent DNA double-strand breaks from X-ray-based cardiac examinations: a randomized, double-blinded, placebo-controlled trial. J Am Coll Cardiol. 2014 Jul 8;64(1):117-8.
  29. Lledó I, Ibáñez B, Melero A, Montoro A, Merino-Torres JF, San Onofre N, Soriano JM. Vitamins and Radioprotective Effect: A Review. Antioxidants (Basel). 2023 Mar 1;12(3):611. doi: 10.3390/antiox12030611.
  30. Park H, Kang J, Choi J, Heo S, Lee DH. The Effect of High Dose Intravenous Vitamin C During Radiotherapy on Breast Cancer Patients’ Neutrophil-Lymphocyte Ratio. J Altern Complement Med. 2020 Nov;26(11):1039-1046.
  31. Prasad KN, Cole WC, Kumar B, Che Prasad K. Pros and cons of antioxidant use during radiation therapy. Cancer Treat Rev. 2002 Apr;28(2):79-91.
  32. Saade C, Ammous A, Abi-Ghanem AS, et al. Body Weight-Based Protocols During Whole Body FDG PET/CT Significantly Reduces Radiation Dose without Compromising Image Quality:Findings in a Large Cohort Study. Acad Radiol. 2019 May;26(5):658-663.
  33. Nautiyal A, Mondal T, Manii M, et al. Significant reduction of radiation dose and DNA damage in 18F- FDG whole-body PET/CT study without compromising diagnostic image quality. Journal of Radiation Research and Applied Sciences,Volume 14, Issue 1, 2021, Pages 358-368.
  34. Lee CI, Haims AH, Monico EP, Brink JA, Forman HP. Diagnostic CT scans: assessment of patient, physician, and radiologist awareness of radiation dose and possible risks. Radiology. 2004 May;231(2):393-8.
  35. https://www.latimes.com/archives/la-xpm-2009-oct-10-me-cedars-sinai10-story.html
  36. Amato E, Salamone I, Naso S, et al. Can contrast media increase organ doses in CT examinations? A clinical study. AJR Am J Roentgenol. 2013 Jun;200(6):1288-93
  37. Mazloumi M, Van Gompel G, Kersemans V, et al. The presence of contrast agent increases organ radiation dose in contrast-enhanced CT. Eur Radiol. 2021 Oct;31(10):7540-7549.
  38. Power SP, Moloney F, Twomey M, et al. Computed tomography and patient risk: Facts, perceptions and uncertainties. World J Radiol. 2016 Dec 28;8(12):902-915.
  39. Doss M. Shifting the paradigm in radiation safety. Dose Response. 2012 Dec;10(4):562-83.
  40. Doss M. Linear No-Threshold Model VS. Radiation Hormesis. Dose Response. 2013 May 24;11(4):480-97.
  41. McMahon SJ. The linear quadratic model: usage, interpretation and challenges. Phys Med Biol. 2018 Dec 19;64(1):01TR01. doi: 10.1088/1361-6560/aaf26a. PMID: 30523903.
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