What Doesn’t Kill You Makes You Stronger

Most people over 50 have some kind of joint and back pain.  We think that when we gain weight, there is more pressure in every step, more strain on the joints, and it makes our arthritis worse.  But the truth is stranger than this.  In fact, exercise helps to prevent and to relieve arthritis [Ref1Ref2, Ref3Ref4].  (The only exception is extreme, punishing exercise, like the elbow of a major league pitcher or the knees of a lineman in pro football.)  Walking around with a 40-pound backpack has the opposite effect of carrying an extra 40 pounds of belly fat.  The reason that weight gain exacerbates arthritis is that every fat cell is a hormone factory, pumping out inflammatory signals.  Together these signals (called cytokines) tell the blood cells to turn up the heat on the inflammatory attack that is eating away at the cartilage in our joints.

Was mich nicht umbringt, macht mich stärker.
— Friedrich Nietzsche

photo_backpainMaybe the fact that overeating is bad for our longevity is so familiar to you that you no longer think it’s strange.  But believe me, it’s strange.  It’s strange that the harder you work your body the longer it lasts.  And it’s strange that life span in lab animals can be modestly extended not by protecting and coddling them, but just the opposite–by challenging them with one hardship or another.  A list of things that have been found to increase life span include

  • low-dose radiation
  • toxins
  • pathogens and infections
  • heat, and
  • cold
  • hypoxia (oxygen starvation)

Paraquat is a powerful herbicide, and highly toxic to humans.  It is the opposite of an anti-oxidant.  When paraquat was sprayed from the air to destroy marijuana fields in Chiapas, Mexico, 16 people died.

In the McGill University laboratory of Siegfried Hekimi, life span of roundworms is extended remarkably by adding paraquat to the medium in which they swim.  Tiny doses of paraquat have little effect, and high doses kill the worms, but if the dose is adjusted just right, the worms live 70% longer.

When challenged, the body adapts by becoming stronger–this much is no surprise.  What makes us stand up and take note and rethink how we’re put together is that the body “over-adapts”.  It becomes so much stronger that we actually are healthier and live longer in the presence of challenges and toxins and hardships than when we are coddled in an ideal, unstressed environment

The name for this general phenomenon is hormesis, and it was first described in the 19th Century.  But the word “hormesis” dates only from 1943, and it is only in the last two decades that the idea has received some scientific respect.  There are three reasons thescientific community has resisted the concept:

  • Association with the problematic science of homeopathy.  In the early 20th Century, people who promoted homeopathic medicine were prominent supporters of the concepts of hormesis.
  • Polluters and chemical manufacturers seized on the idea to argue, opportunistically, that pollution is actually a boon to public health!  In fact, owners of nuclear power plants argue that leakage of radiation is not a problem as long as it is below a threshold dose*.
  • The true strangeness emphasized above.  Hormesis implies that the body is unable to be fully healthy if it has all the food it needs, and is deprived of poisons and stressors.


Examples of Hormesis

  • The most dramatic and obvious examples of hormesis are that less food and more exercise both lead to extended life span.
  • Chloroform is a trace contaminant in toothpaste.  Manufacturers tested the safety of their product by feeding toothpaste to dogs with and without the chloroform.  They were surprised to find that the mortality rate was lower for the dogs that got chloroform [Ref].
  • Repeated, mild burns slow the age-related damage to human skin cells [Ref].  Worms that are exposed to heat shock also live longer [Ref].
  • In an Australian study, people exposed to more sunlight had less long-term UV damage to their DNA [Ref].
  • Rats that were bathed in cold water 4 hours per day lived longer and had lower cancer rates than rats that stayed warm [Ref].
  • Mice exposed to 25 or 50 times the normal background level of gamma radiation lived 20% longer than mice that received only the ordinary background [Ref].
  • Fruit flies exposed to disease enjoyed greater fertility and longer life [Ref].

Don Luckey devoted the last decades of his professional life to documenting the health benefits of radiation exposure, and faced the skeptics to argue that we should all be getting more whole-body radiation exposure than we get from cosmic rays and low background of radioactive elements in the earth [Ref]. The US National Research Council disagrees [Ref].

Edward Calabrese researches the epidemiology of environmental toxins at U Mass.  For 25 years, he reported findings in terms of standard linear models:  If 1 part per million is bad, then we expect half a part per million to be half as bad.  But with accumulating evidence, there came a point where he had to break ranks, and he has been a prominent advocate of the hormetic viewpoint ever since.

From a comprehensive search of the literature, the hormesis phenomenon was found to occur over a wide range of chemicals, taxonomic groups, and endpoints…hormesis is a reproducible and generalizable biological phenomenon, and is a fundamental component of many, if not most, dose-response relationship [Ref].

The Hygiene Hypothesis says that widespread use of disinfectants has reduced childhood exposure to bacteria to an unhealthy extent, and that increased incidence of asthma, irritable bowel syndrome, Crohn’s disease, and various auto-immune disorders has been the result.

Hormesis also has an unusual place in cinematic history. During the 1950s, reports on the capacity of ionizing radiation to stimulate growth inspired the genre of so-called ‘‘nuclear monster’’ movies, which included Godzilla (1954) and Attack of the 50 Foot Woman (1958). Typical of this genre was Them! (1954), in which ants exposed to radiation from atomic bomb tests grow to gigantic proportions and terrorize residents of New Mexico. [Ref]


How to make biological sense of hormesis

The reason that hormesis seems so strange to us is that we like to think that we are evolved to be as strong and as healthy as it has been possible for nature to make us.  It doesn’t make sense for us as individuals to hold back on strength and longevity just because we don’t happen to be starved or poisoned at the moment.  But if we thinkcollectively instead of individually, it all starts to make sense…

My principal contribution to evolutionary theory has been the Demographic Theory of Senescence, which starts from the premise that population overshoot is a danger to most animal species.  If animals eat all the food that is available to them and reproduce as fast is they are physically capable, then the environment will be denuded, the next generation will starve, and the species will face extinction.  All animal species are evolved to avoid this.  [Academic references 2012 and 2006]

Another way to describe this same situation is to say that the main causes of death in nature are all clumped together.  When food becomes scarce, everyone starves at once.  When there is an epidemic, everyone gets sick together.  When there are storms or cataclysms or environmental poisons, they affect an entire population at once.

Aging is nature’s way of leveling out the death rate, assuring that we don’t all die at the same time.  Aging puts our deaths on an individual schedule so we can die at different times; other causes of death tend to kill everyone or no one.

Since aging has evolved to complement the environmental death rate, we expect that when the environment is most hostile, there is little or no need for additional deaths from aging.  So aging takes a vacation during starvation or other times of hardship.  Conversely, when life is easy and stress-free, no one is being killed from external causes, aging is out in full force, helping to thin the population and avoid population overshoot.

So the Demographic Theory provides a natural context for understanding hormesis.  In fact, the Demographic Theory is the only theory of aging in which hormesis is actually a prediction.

(Mikhail Blagosklonny agrees, but stops short of saying that aging is programmed.  Peter Parsons disagrees.)


Implications for Personal Care and Longevity

Well, eat less and exercise more–that’s a good start.  If I were just looking at the data, I’d have to say that introducing a source of gamma radioactivity in the home, 25 times above background might be justified.  But the idea makes me queasy.  We don’t know how to do it well.  Might it be beneficial at some ages and a risk factor at other ages?  People who live in houses with naturally high radon levels have elevated risk of lung cancer [Ref].

The concept of hormesis has made me relax a lifelong fear of pollution, and I have backed off from Bruce Ames’s program of reduced exposure to natural and artificial toxins. But I’m not ready to do anything pro-active to increase my exposure to toxins or radiation.



* My position on nuclear power is that low-level leaks of radioactivity are the least of its problems.  Nuclear power should be a non-starter because it is uneconomic without huge government subsidies, including the Price-Anderson act which limits liability.  Haven’t we learned anything from Chernobyl, Three Mile Island, and Fukushima?  And don’t get me started on guaranteeing the safe storage of radioactive waste for the next 20,000 years.


This article originally appeared on Josh’s blog Aging Matters.