Each hair follicle contains pigment (called melanin — the same thing that colors our skin) that gives our hair its color. As we get older, we produce less pigment, resulting in gray hair. Dermatologists usually use the "50-50-50" rule of thumb which states that at 50 years old, 50 percent of the population has at least 50 percent grey hair.
However, some people go gray early. What's early? As WebMD reports: "Typically, white people start going gray in their mid-30s, Asians in their late 30s, and African-Americans in their mid-40s." So early is before those benchmarks, and its those early gray strands that may indicate a nutritional imbalance.
"Low vitamin B12 levels are notorious for causing loss of hair pigment," says Dr. Karthik Krishnamurthy, director of the Dermatology Center's Cosmetic Clinic at Montefiore Medical Center in the Bronx, New York, tells Good Housekeeping. And a 2013 study found low vitamin D3, serum calcium and serum ferritin levels in people who went gray prematurely.
Early gray hair also can be a sign of a problem with your pituitary or thyroid gland, according to WebMD.