The ubiquity of background radiation and the clinical utility of naturally occurring potassium-40 in human body

The commonly accepted notion that any dose of radiation is carcinogenic is questionable in light of our current appreciation of the evolution of our planet and the life that has quite successfully evolved upon it. The earth was born in an abundant sea of radiation. Thus, the premise of the linear no-threshold hypothesis that extrapolates the risk from radiation exposure at higher levels to that at lower levels in a linear fashion without recognizing a lower limit of risk is of questionable scientific merit and, in our opinion, requires appropriate revision. The presence of natural background radiation and its abundance in the human body is reviewed. One of the naturally occurring radioisotopes in the human body, ⁴⁰K , is discussed as a useful marker of intracellular space of the brain and of muscle mass of the limbs, which measurements may be of relevance for clinical diagnostic purposes.