Friday, July 29, 2016

Ionizing Radiation Adversely Impacts Cardiac Health

A new study came out addressing the impacts of ionizing radiation on the cardiac health of astronauts.

The research study notes that all forms of ionizing radiation have been show to have adverse impacts on the human heart but the ionizing radiation known as HZE is particularly destructive. HZE radiation is galactic radiation consisting of the nuclei of atoms heavier than helium and hydrogen.

Below is the study, references to research on ionizing radiation and cardiac health, and a definition of HZE ions:

Michael D. Delp , Jacqueline M. Charvat , Charles L. Limoli, Ruth K. Globus & Payal Ghosh (2016). Apollo Lunar Astronauts Show Higher Cardiovascular Disease Mortality: Possible Deep Space Radiation Effects on the Vascular Endothelium. Scientific Reports 6, Article number: 29901 (2016). doi:10.1038/srep29901
ABSTRACT: As multiple spacefaring nations contemplate extended manned missions to Mars and the Moon, health risks could be elevated as travel goes beyond the Earth’s protective magnetosphere into the more intense deep space radiation environment. The primary purpose of this study was to determine whether mortality rates due to cardiovascular disease (CVD), cancer, accidents and all other causes of death differ in (1) astronauts who never flew orbital missions in space, (2) astronauts who flew only in low Earth orbit (LEO), and (3) Apollo lunar astronauts, the only humans to have traveled beyond Earth’s magnetosphere. Results show there were no differences in CVD mortality rate between non-flight (9%) and LEO (11%) astronauts. However, the CVD mortality rate among Apollo lunar astronauts (43%) was 4–5 times higher than in non-flight and LEO astronauts. To test a possible mechanistic basis for these findings, a secondary purpose was to determine the long-term effects of simulated weightlessness and space-relevant total-body irradiation on vascular responsiveness in mice. The results demonstrate that space-relevant irradiation induces a sustained vascular endothelial cell dysfunction. Such impairment is known to lead to occlusive artery disease, and may be an important risk factor for CVD among astronauts exposed to deep space radiation.  
Recent epidemiological studies have demonstrated increasing risk for cardiovascular disease resulting from ionizing radiation exposure10,11,12. However, these estimates are largely derived from low linear energy transfer (LET) radiation exposures such as X-rays or gamma rays, which have fundamentally different properties from charged HZE particles comprising the galactic cosmic rays. HZE ions, for example, produce greater adverse effects on cellular physiology through increased genetic alterations and perturbations to redox metabolism, leading to persistent elevations in oxidative stress13,14,15.
Here are the citations for research establishing impacts of ionizing radiation from atomic weapons and medicine. These studies primarily address exposure to gamma (electro-magnetic) and beta radiation (electron/positron):
10. Shimizu, Y. et al. Radiation exposure and circulatory disease risk: Hiroshima and Nagasaki atomic bomb survivor data, 1950–2003. BMJ 340, b5349 (2010).

11. Darby, S. C. et al. Risk of ischemic heart disease in women after radiotherapy for breast cancer. N Engl J Med 368, 987–998, 10.1056/NEJMoa1209825 (2013).

12. Little, M. P. et al. Systematic review and meta-analysis of circulatory disease from exposure to low-level ionizing radiation and estimates of potential population mortality risks. Environ Health Perspect 120, 1503–1511, 10.1289/ehp.1204982 (2012)
HZE ions are similar to alpha particles, which consist of a nucleus of a helium atom. HZE ions by definition are a form of fast moving particle radiation consisting of nuclei of elements heavier than hydrogen: “A nucleus with no orbiting electrons”:
From Wikipedia: HZE ions are the high-energy nuclei component of galactic cosmic rays (GCRs) which have an electric charge greater than +2. The abbreviation "HZE" comes from high (H) atomic number (Z) and energy (E). HZE ions include the nuclei of all elements heavier than hydrogen (which has a +1 charge) and helium (which has a +2 charge). Each HZE ion consists of a nucleus with no orbiting electrons, meaning that the charge on the ion is the same as the atomic number of the nucleus. HZE ions are rare compared to protons, for example, composing only 1% of GCRs versus 85% for protons.[1] HZE ions, like other GCRs, travel near the speed of light. Their source is likely to be supernova explosions.[2]
I've tried several times to find information on whether or not nuclear fission reactors used in commercial energy production can generate HZE ions in a meltdown scenario. I know decay of uranium and radium, among other elements, produces alpha particles but I can find no information about production of HZE ions on earth.

So the potential role of HZE ions on earth is not clear. Regardless, the research cited above does clearly establish that ionizing radiation has adverse impacts on cardiac health and that space radiation poses special dangers.

Cancer is only one of the many detrimental biological effects of ionizing radiation. Leaving earth is not an option for humans until radiation shielding technology is perfected. The Martian scenario played out by Matt Damon is an unrealistic fantasy.

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