Is the whitening limited to only brows or are your scalp hair affected as well? Do you have a family history of premature greying of hairs ? Though treatment options are limited for premature canities, I would say oral medications such as calcium pantothenate or topical formulations are worth a shot. However , these must not be started on your own. You will need a dermatologist who will take a history and suggest the next line of management or treatment accordingly. All the best!