Lack of minerals like zinc, copper is one of the most underestimated yet one of the most analysed reasons for grey hair.
Turning already grey hair into black is not possible after a particular age, but you can always slow down further greying of hair.
A balanced diet is the most effective solution to control greying of hair. Include lots of fresh fruits, vegetables, protein rich sources of food in your diet. Load up on food items containing antioxidant and
vitamin C like gooseberry, oranges, lemon etc.
Try to stay stress free, limit your on-screen time, and do exercises and yoga that will increase oxygen supply to your hair.