@bulldogsandbruins 821 wrote:

What are the causes and can anything be done to slow/reverse the process?

The color of hair is determined by the production of melanin by cells in hair follicles called melanocytes.

When the metabolism of melanocytes is impaired, then the production of melanin is decreased. This causes hair to be non-colored, clear, translucent – a color we call gray or white hair.

Some processes – such as aging or autoimmune destruction of hair follicles when DHT attaches – may cause permanent melanocyte impairment. Aging, itself, reduces catalase enzyme production, which prevents hydrogen peroxide produced by the body from impairing melanin production.

But some may be reversible. These include:
Vitamin B12 deficiency
Thyroid deficiency
Anemia
Biotin deficiency
Folic acid deficiency