While the cancer risks of radiation exposure are well documented, much more research is needed into the effects of low-dose radiation on cardiovascular risk. These are the conclusions of a Comment in this week's edition of The Lancet, authored by Kiyohiko Mabuchi, Parveen Bhatti, and Alice Sigurdson at the National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.
High-dose therapeutic radiation of more than 30-40 Gy — eg, that used in treating breast cancer - is already known to increase the risk of heart disease. However, people with certain non-cancer diseases, eg scoliosis, are exposed to doses much lower than this. There is evidence of a dose-response relation from surviving patients irradiated for peptic ulcer disease with cardiac doses of 1.6-3.9 Gy, which showed such patients had significantly increased risk of heart disease. And a recent study of employees in the nuclear industry in the UK has also revealed a statistically significant association between radiation exposure at much lower doses and cardiovascular disease.
The authors discuss the difficulties of assessing the effects of these low radiation doses effectively, and the problems of excluding 'confounders', ie, other factors applicable to the individual that could be responsible or partly responsible for their heart disease. They point out that radiation could cause damage in the same way as other biological pathways. For example, atherosclerosis is an inflammatory process associated with damage to the endothelial cells that line blood vessels — a pathway that could be shared with radiation-related tissue effects.
Finally, the authors say that the risk of radiation-related heart disease is much lower than that of radiation-related cancer, but due to the uncertainty around the heart-disease risk it is premature to begin estimating the excess number of heart disease cases in an exposed population. They conclude: "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."
Kiyohiko Mabuchi, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA T) +1 301-496-6641 E) mabuchik@mail.nih.gov / nicpressofficers@mail.nih.gov
Full Comment: http://press.thelancet.com/radiation.pdf
Journal
The Lancet