Are Our Bodies Radioactive? - Health Physics

Does human body contain radioactive elements? How do they affect our body?

Have you eaten a banana lately?  Any vegetables?
If the former, you might have some Potassium-40 incorporated into some of your cells.  If the latter, you might have some Carbon-14 in you.

Almost everything we eat has small amounts of radioisotopes, and if there is any nutritional value to what we eat, molecules are absorbed and incorporated into our body, which can include radioisotopes.

What do they do?
They decay radioactively, and can cause mutations in your DNA or destruction of certain biological macromolecules!
But wait!  Isn't that how cancer starts?
Well, yes, but it's also an extremely common occurrence, and our cells are replaced very often in a process called "turnover".  If DNA is damaged, most of the time the cell will kill itself in a controlled manner (called "apoptosis"), and nearby cells will replicate (if they still can) to replace the dead cell and recover some of it's contents.  The damaged cell may kill itself in an uncontrolled manner (called "necrosis"), but when only a small number of cells necrosis, they are easily replaced.

Okay, so then how does radiation cause cancer?
Cancer is produced when radiation causes damage that prevents apoptosis and/or necrosis (and many times allows for unregulated replication of that cell).  This is a chance event (with a very small probability relative to the number of mutations that occur to our cells every day of our life).

How much cell turnover is good/bad?
Well, this is a contentious and continuously debated point in the radiation safety community.  Supporters of the "Linear No-Threshold Hypothesis" say that lower radiation exposure is always better, which means that minimizing cell turnover due to radiation is the goal.  Supporters of the "Radiation Hormesis Hypothesis" say that, below a certain threshold of radiation dose, radiation can stimulate the immune system and have certain beneficial properties.  That is, low levels of radiation can increase the turnover rate of certain cells involved in the immune system, and this can have benefits to the human in terms of overall health.

Studies have gone both ways, sometimes showing increased risk of cancer due to increased background radiation levels, other times correlating decreased risk of cancer with high background radiation levels that are below the "threshold" dose.

So, are radioisotopes inside the human body good or bad?
We really can't say either way for certain, just yet.
However, it is safe to say that in both cases, the extra risk produced by the radioisotopes you currently have in your body is negligibly small.  Better to be worried about your doses from dental x-rays!