There are nuclear reactions happening in our bodies, though they are very subtle and not harmful. These reactions are mainly related to naturally occurring radioactive isotopes and cosmic rays interacting with our body.

One example is the presence of potassium-40, a naturally occurring radioactive isotope. Potassium-40 makes up a small fraction of the potassium in our bodies and undergoes radioactive decay, which is a form of a nuclear reaction. This decay process can result in the emission of beta particles (electrons) or gamma rays, both of which are types of radiation. Despite this, the levels of radiation are extremely low and pose no health risk.

Another example is the interaction of cosmic rays with the atoms in our bodies. Cosmic rays, which are high-energy particles from space, occasionally collide with atomic nuclei in our bodies, causing nuclear reactions. These reactions can produce small amounts of radioactive isotopes, but again, the levels are so low that they are not harmful.

In summary, while nuclear reactions do occur in our bodies, they are natural, very low in intensity, and do not pose any danger to our health. These processes are just a part of the natural background radiation we are all exposed to throughout our lives.