Heart Risk Due To Low Radiation Doses Worth Investigating Say Scientists
Featured ArticleMain Category: Heart Disease
Also Included In: Radiology / Nuclear Medicine
Article Date: 29 Aug 2008 - 3:00 PST
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Scientists at the National Cancer Institute in the US say more research is needed into the effects of low-dose radiation on cardiovascular risk, an area that remains controversial and about which there is too much uncertainty to give reliable estimates of numbers affected, compared to the well documented risks of cancer from radiation exposure.
This the conclusion of a Comment in this week's issue of The Lancet, written by Drs Kiyohiko Mabuchi, Parveen Bhatti, and Alice Sigurdson from the National Cancer Institute, which is part of the National Institutes of Health in Bethesda, Maryland.
There is evidence that high dose radiation of more than 30-40 Gy, such as that used to treat Hodgkin's lymphoma and breast cancer, increases the risk of heart disease. But what is less clear is the risk for people who are exposed to much lower doses, such as patients with non-cancer diseases like scoliosis and ankylosing spondylitis. While patients being treated for non-cancer conditions have been included in extensive epidemiological research, few of the studies have evaluated the effect of dose-response on cardiovascular as opposed to cancer risk, wrote the authors.
(Gy is short for gray, a unit of absorbed radiation that is equal to one joule of radiation energy absorbed by one kilogram of matter.)
What little evidence there is, suggests there could be a significant relation between low dose radiation and cardiovascular risk, but there are many difficulties because of the problems of excluding other factors that could be involved, the so-called "confounders" that obscure the statistics or make it look like there is a link when there isn't when you remove the effect of these other factors on heart disease.
For instance, there is evidence that surviving patients who were treated with radiation for peptic ulcer showed a significantly increased dose-response related risk of heart disease from cardiac doses of 1.6-3.9 Gy. And another study of workers in the UK nuclear industry also suggested a statistically significant link between exposure to low dose radiation and cardiovascular disease.
The authors suggest there are plausible biological explanations for how low dose radiation might damage cardiac tissue, for example the biological mechanisms that underlie inflammatory processes like atherosclerosis that damage the endothelial cells that line blood vessels could be similar to the effect of radiation-related tissue changes.
The authors conclude that there is too much uncertainty to be able to give reliable estimates of the number of extra heart disease cases that occur because of low-dose radiation and that:
"Further investigations are needed to sort out effects of radiation and confounders in existing and planned studies of radiation-exposed cohorts, and new laboratory studies are needed to explore biological mechanisms for low-dose radiation-related cardiovascular effects."
"The low-dose radiation effects on cardiovascular disease risk are likely to remain challenging and controversial -- even more so than the linear no- threshold arguments for cancer risk that are debated to this day -- but should not be dismissed," they added.
"Can low-dose radiation increase risk of cardiovascular disease?"
Parveen Bhatti, Alice J Sigurdson, Kiyohiko Mabuchi.
The Lancet, Volume 372, Number 9640, 30 August 2008, pages 697-699.
Click here for full text of Article (subscription required).
Sources: The Lancet.
Written by: Catharine Paddock, PhD
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today
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Heart Risk Due To Low Radiation Doses: Additional Evidence
posted by Egan Oconnor on 2 Sep 2008 at 2:39 am Very strong evidence exists supporting the hypothesis that medical imaging by fluoroscopy and planar x-rays is an important causal co-actor in ischemic heart disease (IHD) as well as in human cancer --- an hypothesis described in Medical News Today, 29 Aug 2008 (“Heart Risk Due to Low Radiation Doses Worth Investigating Say Scientists,” by Catharine Paddock, PhD).
This evidence was uncovered and published in 1999 in a monograph (ISBN 0932682979) entitled Radiation from Medical Procedures in the Pathogenesis of Cancer and Ischemic Heart Disease: Dose-Response Studies with Physicians per 100,000 Population, by the late John W. Gofman, M.D., Ph.D. His previous pioneering accomplishments in scientific research are described in an obituary (now online at http://www.berkeley.edu/news/media/releases/2007/09/04_GofmanObit.shtml ) .
Unfortunately, his wife’s failing health and then his own failing health prevented him from presenting his new findings widely. But fortunately, the complete monograph is available from http://www.amazon.com and its Executive Summary, table of contents, extensive reference list, and its first five chapters are available, free, online at http://www.ratical.org/radiation/CNR/RMP/execsumm.html . On the same site are the six main critiques by peer-reviewers at http://www.ratical.org/radiation/CNR/RMP/6critiques.html.
His findings about x-ray induced IHD fell out of the age-adjusted mortality rates in the United States from all major causes of death at mid-century --- data that Professor Gofman studied in order to make a reality check on the grim possibility that accumulated lifetime exposures to medical x-rays (including fluoroscopy) became a major contributing cause of cancer during the 20th century.
As a result of his dose-response studies, Professor Gofman proposed that lifetime accumulated exposures to medical x-rays may well be a necessary causal co-actor in over half of the age-adjusted mortality rates in the United States both from cancer and from ischemic heart disease. In other words, over half the current baseline cancer and IHD mortality rates might well be absent in the absence of past exposure to medical x-rays.
The “over 50%” estimates are necessarily ballpark estimates --- meaning a lack of appropriate data requires the use of several important approximations and assumptions, forthrightly identified in the book. The familiar estimate, that medical x-rays account for only 1% of the U.S. cancer burden, is also a ballpark estimate.
If you are deeply doubtful that x-rays could do so much harm without anyone recognizing it --- despite 100 years of their use in medicine --- the reasons become clear in Chapter 2 of the monograph, http://www.ratical.org/radiation/CNR/RMP/chp2F.html . The abbreviated explanation is that past x-ray doses have seldom been measured, although they have been a proven mutagen since 1929. There are no data on anyone’s lifetime accumulated doses to each organ. In addition, the cumulative unmeasured x-ray doses badly undermine risk-values extracted from study of persons exposed to ionizing radiation from non-x-ray sources (Japanese atomic bomb survivors, nuclear workers, airline flight personnel).
If these problems obscured very large risks from x-rays so well --- Dr. Gofman missed them for nearly 20 years --- why did he decide it was imperative to make a reality-check on the ballpark 1% estimate mentioned above? The story unfolds in Chapter 2. And how did he do it? He designed a novel method, set forth in detail in Chapters 3 and 4, which delivers its own ballpark estimate. No one can do better than “ballpark,” for the reasons stated above.
Despite natural doubts about his findings, your intellectual curiosity and responsibilities should persuade you to look at six unforgettable graphs from his monograph: http://www.ratical.org/radiation/CNR/RMP/chp1F.html#fig1a .These graphs plot age-adjusted mortality per 100,000 persons (males and females separately) versus physician-density per 100,000 persons, by Census Divisions. The necessary approximation (supported elsewhere in the mainstream literature) is that the average number of x-rays given per 100,000 population is approximately proportional to the number of physicians per 100,000 population, in each of the nine U.S. Census Divisions.
The analysis uncovered a startling similarity between the positive dose-responses from cancer and from ischemic heart disease. Quite intriguing. Statistically extremely significant too. By contrast, the flat or negative dose-responses for noncancer nonIHD causes of death look extremely different. Just by accident?
Because correlation alone cannot prove causation, Dr. Gofman considered other explanations, besides x-rays, for these powerful relationships (Chapter 68), and could find none better (Chapter 69). Therefore, he proposed that mutations acquired in the coronary arteries can be atherogenic, just as mutations in other organs can be carcinogenic. Indeed, acquired (non-inherited) mutations would explain why atheromas grow in distinct places and not everywhere in the coronary arteries. Dr. Gofman, the highly honored “father of clinical lipidology,” proposes in Chapters 45 and 46 how atherogenic mutations and atherogenic plasma lipoproteins may interact.
Prior to the very strong findings in his 1999 monograph, Dr. Gofman had regarded earlier evidence as too “thin” to believe that acquired mutations in the coronary arteries might initiate or accelerate atheromas. Astonished by his own new findings, he reviewed the earlier evidence and proposals by others, including some supportive experimental animal studies, described in Chapter 44, Part 8, and in Appendix J, Part 5c (“Observations of Synergism between [Ionizing] Radiation and Cholesterol”).
As Medical News Today indicates in its title, a causal relationship between low-dose ionizing radiation and IHD is “worth investigating” further. The growing use of fluoroscopy and CT in medicine makes it imperative to become familiar with verbatim excerpts from three major reports on the “safe-dose fallacy,” provided in Appendix B of the 1999 monograph.
Ms. Egan O’Connor, September 1, 2008, San Francisco.
(Dr. Gofman’s co-worker on radiation issues for 35 years,
and editor of his last five radiation monographs.)
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