KRYPTONITE: Nightmare for Superman?

Do you wonder why kryptonite is dangerous for Superman?
According to Superman story, this fictional kryptonite was produced from the material of Superman’s native planet Krypton when it was destroyed in an explosion.

If Superman is exposed to kryptonite, he gradually becomes weak. Long term and high level exposure can be fatal.
As a background, did you know that Superman’s power comes from the Earth’s yellow sun? His cells absorb electromagnetic radiation. Superman possesses extraordinary powers, traditionally described as, "faster than a speeding bullet, more powerful than a locomotive, and able to leap tall buildings in a single bound." Superman's famous arsenal of powers include flight, super strength, invulnerability, super speed, vision powers (including x-ray, heat, telescopic, infra-red, and microscopic vision), super photographic memory, super hearing, and super breath, which enables him to freeze objects by blowing on them.
Kryptonite is usually found in the form of glowing green rock or metal, with some crystalline formations. Like radioactive Earth elements, kryptonite emits radiation. The radiation seems to behave like gamma ray or X- ray, which can penetrate objects and living bodies. In post comics, long- term exposure to it is known to have the same effects on human beings as exposure to Earth- born radioactive materials; these effects include cancer.
“Kryptonite’s radioactivity may interrupt some organic process with Superman’s body. It might displace the solar radiation responsible for Superman’s powers.
It possibly interferes with semi- photosynthetic process, driving the energy out of his cells in a painful fashion. As a result, Superman can no longer take the advantage of the powers yellow sun gives him. And he loses his powers and may die.”