Colonizing other planets means living with increased radiation. Starting in 1969, when the first of 24 astronauts ventured beyond both our planet›s atmosphere and its magnetosphere, they left behind all layers of cosmic ray protection. US astronaut Shannon Lucid cites this hazard as the biggest challenge in space exploration.
It may already have cost some astronauts their lives. Five of the original space pioneers have died of cancer. Alan Shepherd publicly wondered if his Apollo radiation had given him the leukemia that ultimately killed him.
Most of us have a personal stake in this issue. Many have had CT scans unaware that a single whole body scan can deliver as much radiation as was received by Hiroshima survivors a mile from ground zero. Should we worry?
Maybe, but perhaps not. Nuclear safety experts have long known about lethal radiation doses thanks to unfortunate accidents to workers assembling nuclear weapons. There have even been several suicides and murders using radioactive materials. All this confirmed that an exposure to 1000 rems (using a common but now antiquated measurement system) is usually fatal. For comparison, astronauts landing on Europa’s icy surface would receive 540 rems, which would be lethal in less than a day.
Accidents such as Chernobyl in 1986 plus studies of the 1945 Nagasaki and Hiroshima survivors show that lower-than-lethal doses can result in various cancers 20 years later. So early on, researchers created a paradigm now known as the LNT — the linear no-threshold model, by graphing fatalities and eventual cancers caused by various radiation doses and charting them backward to assess the unknown consequences of low exposures. They guessed that radiation has no safe threshold. That no matter how small the dose, some DNA would be damaged and some percentage of these people would eventually get cancer.
If true, we should be careful about medical scans that use radiation (as opposed to ultrasound probes, which merely employ sound.) We might even watch how many bananas we eat, since a single banana delivers more radiation (from potassium-40) than we’d get by living next door to a nuclear power plant for a whole year.
Epidemiologists then studied large groups of people exposed to small amounts of radiation. For example, they conducted a decade-long medical survey of 70,000 residents living at a radioactive, thorium-contaminated black sand beach in Kerala, India.
They got a surprise. Their incidence of cancer, like that of Hiroshima, Nagasaki and Chernobyl survivors, were far below the rates predicted by the LNT model. In most cases, the cancer rate was less than the control groups. Their radiation exposure had apparently protected them from cancer!
Taken aback, researchers revisited previous animal studies that indeed showed a protective, beneficial effect from low radiation doses. Could such small radiation doses actually be good for you? This possibility, called radiation hormesis, has a sound biological basis. All animals and people are exposed to continuous low-dose radiation from cosmic rays and such. The body routinely repairs such genetic damage. So when rats are exposed to low dose radiation, it seems to prime, harden and shield them from the results of getting a later, larger zap. They’re even protected from other carcinogens.
Radiation hormesis suggests that, even if Europa remains off-limits, astronauts would do fine in the slightly-above-normal radiation background on the Moon or Mars. Back home, it would mean there’s no reason to decline dental X-rays. Indeed, some Japanese clinics now offer low radiation “treatments” based on the purportedly protective effects of hormesis.
That it’s healthful to get small doses of something that would harm you in higher amounts is not a new idea. It certainly applies to things like iron and iodine supplements, and careful UV exposure, that makes the body generate the most ideal form of vitamin D.
In 2005, the prestigious Journal of Radiology ran an article that concluded, “The linear-no-threshold (LNT) hypothesis for cancer risk is scientifically unfounded and appears to be invalid in favor of a threshold or hormesis. This is consistent with data both from animal studies and human epidemiological observations on low-dose induced cancer. The LNT hypothesis should be abandoned. . .”
More studies are underway. One of them keeps animals in a zero-radiation environment so that they’re shielded even from the normal earthly background of 360 microsieverts per year. Will they die sooner when deprived of all radiation?
It’s too early to know. The biggest health organizations continue to advise avoiding unnecessary radiation, and hormesis remains controversial. But even at this early stage it merits our attention, since it may affect our planetary colonization dreams.