The Nikkei news service is reporting that since its December 1 launch in Japan, Wii Fit has sold a million units. Wii Fit first debuted in July last year at the Electronic Entertainment Expo in Santa Monica and garnered mixed reviews.

Wii Fit turns the living room into a fitness center for the whole family with Wii Fit and the buy Wii Balance Board. The ‘game’ offers a “core” workout and compares results and progress on a new channel on the Wii Menu. Workouts include Aerobic exercise, Muscle conditioning, Yoga poses and Balance games.

The title also keeps a track of the users BMI (Body Mass Index) and gives a users ‘Fitness Age’, sort of like how brain training gives the player their brain age. The Fitness Age is measured by factoring the user’s BMI reading, testing the user’s center of gravity and conducting quick balance tests.

With one million units of Wii Fit sold in a month, that’s a lot of fit Wii users in Japan.