HealthPhysics.md

Health Physics

2013-08-14

How many linear relationships in biology persist over more than 6 orders of magnitude?

Whether a given dose is hormetic or deleterious should depend on the stress on the animal at the time of exposure. I conjecture that wartime stress could be responsible for deleterious effects in Japanese bomb survivors at ~ 100mSv, compared to other exposure cases that suggest hormetic effects at that dose.

The doubling dose for double-strand breaks is about 1.5 Gy per cell cycle.¹ That is, ROS from normal metabolism are worth about 0.3 Gy/hour. DNA repair machinery is nearly at capacity at that level, so an additional 1.5 Gy can be deadly. Exercise seems to derive its benefits from stimulating the same systems ²³ and whether it is good or bad also depends on one's existing stress level. Exercising a fatigued person is deleterious, but exercising a sedentary person is beneficial.

If oxidative stress is hormetic, antioxidant supplements may be harmful.⁴

See also:

NAS panel 'misled the world' when adopting radiation exposure guidelines

New clues about the risk of cancer from low-dose radiation

DNA damage (DSBs in particular) may be essential to learning

LNT falsified in two species of bacteria

Another nail in the coffin of the 'accumulated damage' theory

Antioxidant from D. radiodurans protects mice from ionizing radiation

Anthracyclines induce DNA-damage-mediated protection against sepsis

"effective low doses of ionizing radiation act via creation of an anti-inflammatory phenotype in inflamed tissue"

Treatment of Alzheimer's Disease with CT Scans (case report)

X-Erase

2016-08-06

Q: Can you tell me in simple terms why this product is utter nonsense?

A: There's no such thing as "cell ionization". Ionizing radiation (like X-rays) can create ions. But these are electrically charged atoms or molecules, not entire cells. Ions tend to undergo chemical reactions, forming neutral products. Such reactions are generally only harmful when they involve DNA.

Once DNA is damaged it can only be fixed with knowledge of what its sequence should be, and nano-machines capable of using this knowledge to do the repair. Not by "drawing out electrostatic charges".

Fortunately our cells are full of machines like that. You'd be dead in a few hours without them. That's because the reactive molecules created by radiation are the same ones created by burning sugar.⁵ Cells burn lots of sugar so they need to have a way of dealing with it.

You can potentially prevent the damage with antioxidant supplements: you flood your cells with chemicals that can react with the ions, in hopes the ions hit them before hitting any DNA.

Unfortunately this protects cancerous cells too. Cancer cells may even benefit more, because they burn sugar at higher rates than healthy cells. Oxidative damage is a big killer of pre-cancerous cells and it may not be a good idea to go around preventing it.⁶

Also, our DNA repair machines are self-regulating. They respond to need like many other processes in the body. If you live in an area with high background radiation, your repair machinery beefs itself up. This is one reason exercise (deliberately burning sugar faster) can be good for you – it exercises your DNA repair machinery. Antioxidants have been shown to prevent some of the benefits of exercise.²

In summary, radiation isn't special, and oxidative damage is bad but also fundamental to life and preventing it willy-nilly probably isn't a good idea. Fortunately, this medical device thing has no chance of doing that.

All this applies to ionizing radiation, which is any radiation with enough energy to ionize atoms (generally by knocking some electrons off, leaving a positive charge because the protons in the nucleus are no longer counterbalanced). Lower-energy radiation like microwaves can't do that. It can only make things warmer.

Footnotes

1. Vilenchik, Knudson 2003 http://doi.org/10.1073/pnas.2135498100 ↩

2. Ristow et al 2009 http://doi.org/10.1073/pnas.0903485106 ↩ ↩²

3. Watson 2013 http://doi.org/10.1098/rsob.120144 ↩

4. Bjelakovic et al 2007 http://doi.org/10.1001/jama.297.8.842
   Though note, not all included studies were controlled, so the effect may be due to things like risk homeostasis, where people 'spend' the presumed benefits of vitamins by undertaking additional unhealthy behaviors. ↩

5. Resting metabolism is worth about about 300 mSv/hour. ↩

6. There's a limit to what cellular DNA repair machinery can handle. This is why radiation can cure cancer – the extra damage pushes cancer cells over the edge first because they're already sustaining more than healthy cells. ↩