Zinc is an important element to the human body in general and hair in specific. If you are proved by blood test to be deficient, it is very important you blood values for this are within the given range. In most laboratories this is 11-18 umol/L.
If an individual decided to take a zinc supplement regardless (for example because a friend felt better when taking) this could promote an excess of zinc which would, like any other potential overdose, be harmful.
I specialise in male and female hair loss, and a detailed assessment is necessary to decide on the particular treatment needed for an individual. Zinc can actively slow down the rate of testosterone converting to dihyrotestosterone in the conditions zinc applies to. These are known as Androgenic Alopecia and possibly in those androgen sensitive women, for example those with Polycystic Ovarian syndrome.
At Sussex Trichology it is often discussed that Zinc is an essential mineral which plays a part in the immune system, tissue repair and hair growth and hair regrowth. Zinc is a co-factor in the synthesis of protein (link to protein article) and cell division which is most important in forming the bonds which develop the hair shaft.
As with many other vitamins and supplements, a general multivitamin is most useful to boost a balanced diet. I don’t feel the hair, skin and nail supplements are suitable as they are rather general in who they treat (not age appropriate) and there is no scientific proof that the alternatives contained in these (for example green tea) are beneficial enough to take in tablet form. Could the individual not simply drink green tea? Nutritionally Zinc is present in fortified cereals, oily fish, cashew nuts, lobster etc.
A more in depth discussion on the specific points relevant to each patient and their condition, is held during the initial hour consultation.