I was reading a book on radiation biology, and the book describes the process of "indirect action", where radiation can first ionize a water molecule forming a free radical, which then may interact with important cellular molecules, such as DNA. This contrasts with "direct action" which involves direct ionization of a key cellular molecule.

The book states that as hydration increases, the probability of indirect action occurring increases. Given that indirect action normally predominates over direct action in cells, could this mean that over-hydration could be a risk factor for developing cancer in humans? Has there been any research into this?

In addition, would larger humans, who obviously have a larger bodily water content, have an increased risk of developing cancer compared with smaller humans?

  • $\begingroup$ What do you mean by over-hydration? Humans consist to a high percentage of water - it is present in every cell and necessary for out biochemical reaction, so there is already plenty of water present. $\endgroup$
    – Chris
    Commented Nov 20, 2014 at 6:53
  • $\begingroup$ @Chris, I don't mean any strict definition of "over-hydration". If a human is dehydrated, the intracellar water volume will decrease, and if a human has renal impairment leading to anuria, it is likely intracellular water volume will increase. So by overhydration I simply mean more intracellular water than otherwise, that may result from increased water intake, or decreased water excretion. $\endgroup$
    – Kenshin
    Commented Nov 20, 2014 at 6:59

1 Answer 1


In the most technical sense, yes. In a practical sense, no. Average background radiation dose from food and water sources is ~.3 mSv according to the UN. Given that it takes 1 full Sv to increase cancer risk by ~5-6%, it seems unlikely that, under normal conditions, variability in consumption of water will change risk in a significant fashion.

Now, when dealing with highly contaminated water, there may be a more exaggerated effects, scaling with an increased concentration of radioactive particles per unit of water. Of course, in highly radioactive situations the risk of radiation poisoning may be a more immediate worry.


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