Exposure to low-dose radiation linked to increased heart disease risk

A recent study discovered that being exposed to low doses of ionizing radiation is linked to a slight rise in the risk of developing heart disease.

The study's results "have implications for patients who undergo radiation exposure as part of their medical care, as well as policymakers involved in managing radiation risks to radiation workers and the public," say scientists in the press release.

A link between low radiation levels and heart disease

While it is well known that exposure to high radiation levels can harm the heart, scientific evidence now links low radiation levels to heart disease. This includes instances such as exposure to scatter radiation from radiotherapy or working in the nuclear industry.

For the analysis, an international team of scientists analyzed scientific databases to identify studies investigating the potential connections between various cardiovascular diseases and exposure to radiation, primarily from radiotherapy and occupational sources.

Considering critical factors such as the individual's age at the time of exposure, scientists discovered consistent evidence that a higher radiation dose was associated with a greater risk of developing cardiovascular diseases. The risk increase was proportional to the amount of radiation received, spanning a wide range of radiation doses.

The study discovered that the risk of developing cardiovascular disease increased with the amount of radiation exposure, with each gray (Gy) of radiation increasing the relative risk. Furthermore, for specific types of cardiovascular disease, the risk was higher for lower doses of radiation (less than 0.1 Gy) and when exposure occurred over an extended period (multiple exposures over hours to years).

The underlying mechanisms are not well understood

According to the authors, the underlying mechanisms behind the cardiovascular effects of radiation, even at high doses, are not well understood.

They also recognize that few studies have explored how lifestyle and medical risk factors, such as smoking, obesity, diabetes, high blood pressure, and high cholesterol, could potentially modify the risk of developing cardiovascular disease from radiation exposure. So there is still a need for further research in this area.

Researchers note that the findings support an association between acute high doses and, to a lesser extent, chronic low doses of radiation exposure and most cardiovascular diseases. They also suggest that "radiation detriment might have been significantly underestimated, implying that radiation protection and optimization at low doses should be rethought."

Analysis of the latest evidence was published in The British Medical Journal on March 8.

Study abstract:

Objective: To systematically review and perform a meta-analysis of radiation associated risks of cardiovascular disease in all groups exposed to radiation with individual radiation dose estimates.

Design: Systematic review and meta-analysis.

Main outcome measures: Excess relative risk per unit dose (Gy), estimated by restricted maximum likelihood methods.

Data sources: PubMed and Medline, Embase, Scopus, Web of Science Core collection databases.

Eligibility criteria for selecting studies: Databases were searched on 6 October 2022, with no limits on date of publication or language. Animal studies and studies without an abstract were excluded.

Results: The meta-analysis yielded 93 relevant studies. Relative risk per Gy increased for all cardiovascular disease (excess relative risk per Gy of 0.11 (95% confidence interval 0.08 to 0.14)) and for the four major subtypes of cardiovascular disease (ischaemic heart disease, other heart disease, cerebrovascular disease, all other cardiovascular disease). However, interstudy heterogeneity was noted (P<0.05 for all endpoints except for other heart disease), possibly resulting from interstudy variation in unmeasured confounders or effect modifiers, which is markedly reduced if attention is restricted to higher quality studies or those at moderate doses (<0.5 Gy) or low dose rates (<5 mGy/h). For ischaemic heart disease and all cardiovascular disease, risks were larger per unit dose for lower dose (inverse dose effect) and for fractionated exposures (inverse dose fractionation effect). Population based excess absolute risks are estimated for a number of national populations (Canada, England and Wales, France, Germany, Japan, USA) and range from 2.33% per Gy (95% confidence interval 1.69% to 2.98%) for England and Wales to 3.66% per Gy (2.65% to 4.68%) for Germany, largely reflecting the underlying rates of cardiovascular disease mortality in these populations. Estimated risk of mortality from cardiovascular disease are generally dominated by cerebrovascular disease (around 0.94-1.26% per Gy), with the next largest contribution from ischaemic heart disease (around 0.30-1.20% per Gy).

Conclusions: Results provide evidence supporting a causal association between radiation exposure and cardiovascular disease at high dose, and to a lesser extent at low dose, with some indications of differences in risk between acute and chronic exposures, which require further investigation. The observed heterogeneity complicates a causal interpretation of these findings, although this heterogeneity is much reduced if only higher quality studies or those at moderate doses or low dose rates are considered. Studies are needed to assess modifications of radiation effect by lifestyle and medical risk factors in more detail.