Unfortunately, there is no scientific evidence that any diet, herb, supplement, or natural product can prevent or reverse gray hair, however, there are some underlying conditions that can cause hair to go prematurely gray and some ancient approaches you might be interested in.
Each one of us has a genetically predetermined time when our hair will begin to turn gray. Although nothing can stop this, there are some conditions that can cause hair to gray earlier or more quickly than normal, such as thyroid disorders, vitamin B12 deficiency, and vitiligo.
In traditional Chinese medicine (TCM) and Ayurveda, the traditional medicine of India, premature gray hair reflects an underlying disturbance. Read the full answer: Natural Help for Gray Hair?