I think the answer is a cell..
The formulation of zinc that has been found somewhat effective in treating the symptoms of the common cold is the zinc gluconate. Zinc gluconate may also be used to treat and to prevent zinc deficiency. Zinc is an important mineral for growth and for the development and health of body tissues.
Humans are warm blooded and can't be cold blooded because of the environment we live in. We can't sit still during the winter and soak up warmth from the sun.