ZincSerum zinc
A mineral essential to immunity, healing and testosterone production.
Zinc is required by hundreds of enzymes and by the proteins that switch genes on and off. It has particular roles in immune function, wound healing, taste and reproductive hormone production.
It matters as a nutrient, but serum zinc is an imperfect way to measure status: the body regulates the blood level, and it falls during infection and inflammation as zinc is redistributed into tissues, which can look like deficiency when it is a response.
In practice results are interpreted alongside inflammatory markers and, where it matters, a fasting morning sample is used, since zinc drops after meals and through the day.