Yes, HEALTHIER is a Scrabble word!

Letter values in Scrabble US: H 4, E 1, A 1, L 1, T 1, H 4, I 1, E 1, R 1.

Is it a valid word?

HEALTHIER is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

improved in health or physical condition
having or indicating good health in body or mind; free from infirmity or disease
financially secure and functioning well
promoting health; healthful
exercising or showing good judgment
large in amount or extent or degree

Also: good for you, level-headed.