Astronomy

10 ASTRONOMY • APRIL 2018

I

f we’re ever to colonize

other planets, we’ll have to

deal with increased radia-

tion environments. Starting

in 1969, 24 astronauts

ventured beyond Earth’s atmo-

sphere and magnetosphere,

leaving behind all layers of cos-

mic ray protection. U.S. astro-

naut Shannon Lucid cites this

hazard as the biggest challenge

for manned space exploration.

It may already have cost

some astronauts their lives. Five

of the original space pioneers

have died of cancer. Alan

Shepard publicly wondered if

his Apollo radiation exposure

had given him the leukemia

that ultimately killed him. And

studies show that radiation is

particularly bad for the heart.

Many of us have a personal

stake in this issue. Some of us

have undergone whole-body CT

scans, each of which could have

delivered as much radiation as

Hiroshima survivors received a

mile away from ground zero.

Should we worry? Maybe, but

maybe not. Nuclear safety

experts have long known about

lethal radiation doses, after

unfortunate accidents involving

workers assembling nuclear

weapons and several instances

when uranium-235 in power

plants went supercritical. There

have even been several suicides

and suicide attempts (a radio-

logical worker in Moscow, a

radiographer in the U.K.), as

well as murders (Alexander

Litvinenko, Roman Tsepov,

Vladimir Kaplun) using radioac-

tive materials. All this has con-

firmed that exposure to 1,

rems (a common but now

STRANGEUNIVERSE

Everything in moderation — even radioactivity.

BY BOB BERMAN

Is radiation

beneficial?

antiquated classification; 1 rem

equals 0.01 sievert, the modern

SI unit) is usually fatal. For com-

parison, astronauts landing on

Europa’s icy surface would

receive 540 rems (5.4 Sv), which

is lethal in just a couple of hours.

Accidents such as Chernobyl,

plus studies of the Nagasaki

and Hiroshima survivors, show

that sublethal doses can result

in cancer 20 years later. So early

on, health physicists created a

paradigm now known as the

LNT — the linear no-threshold

model — by graphing fatalities

and cancers caused by various

radiation doses, working back-

ward to assess the consequences

of very small exposures.

They guessed that there is no

safe threshold for radiation: No

matter how small the dose,

some DNA will be damaged,

and some percentage of people

will eventually get cancer. If this

is true, then we should be care-

ful about getting CT scans. We

might even watch how many

bananas we eat, since each gives

us more radiation from potas-

sium-40 than we’d get by living

next to a nuclear power plant

for a year (though still just

1/100th the daily dose we get

simply by living on Earth).

To test their hypothesis, epi-

demiologists studied large

groups of people exposed to

small amounts of radiation. For

example, there is a decade-long

medical survey of 70,000 resi-

dents living near a radioactive

thorium-contaminated black

sand beach in Kerala, India.

They got a surprise. Cancer

rates in Kerala residents, and in

Hiroshima, Nagasaki, and

Chernobyl survivors, are far

below the rates predicted by the

LNT model. In some cases, the

cancer rate was less than in

control groups. Their radiation

exposure had apparently pro-

tected them from cancer!

Ta ken aback, re s e a rchers

revisited animal studies that had

indeed showed a protective, ben-

eficial effect from low radiation

doses. Could small radiation

doses actually be good for you?

This possibility, called radiation

hormesis, has a sound biological

basis. All animals are exposed to

continuous low-dose radiation

from cosmic rays and such. The

body is accustomed to repairing

such genetic damage. When rats

are exposed to low-dose radia-

tion, it seems to prime, harden,

and shield them from the results

of getting a later, much larger

radiation zap. They’re even pro-

tected from other carcinogens.

If true, radiation hormesis

means that, even should Europa

remain off-limits, astronauts

might do fine on the Moon or

Mars. Back home, there’s no

reason to decline dental X-rays.

The idea that it’s healthful to

get small doses of something

that would harm you in higher

amounts is not new. It’s the

founding principle of homeopa-

thy. It certainly applies to

things like fasting, stress, and

iron or iodine supplements.

In 2005, the British Journal of

Radiology published an article

by Ludwig E. Feinendegen,

M.D., a member of the Medical

Advisory Board at Advanced

Medical Isotope Corp., conclud-

ing, “The linear-no-threshold

hypothesis for cancer risk is

scientifically unfounded and

appears to be invalid in favour

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 and be replaced by a

hypothesis that is scientifically

justified.”

More studies are underway.

One involves putting animals

in a zero-radiation environ-

ment shielded even from the

normal earthly background of

360 microsieverts per year. Will

they die sooner when they’re

deprived of all radiation?

It’s too soon to know. The

biggest health organizations

continue to advise avoiding

unnecessary radiation, and

hormesis remains controver-

sial. But even at this early stage,

it’s amazing enough to deserve

our attention, since it may

affect the planetary destinies of

the human race.

BROWSE THE “STRANGE UNIVERSE” ARCHIVE AT http://www.Astronomy.com/Berman.

Water surrounding the core of the Advanced Test Reactor glows bright blue because of

an effect called Cherenkov radiation. ARGONNE NATIONAL LABORATORY

The idea that it’s healthful to get small doses

of something that would harm you

in higher amounts is not new.

Join me and Pulse of the Planet’s

Jim Metzner in my new podcast,

Astounding Universe, at

http://astoundinguniverse.com.