Supports immunity bones muscle and teeth in a chewable tasty and convenient way quest forte d 4000 provides 4000iu of vitamin d3 per chewable tablet vitamin d contributes to the normal function of the immune system and muscles it is needed for the utilization of calcium in the body to help maintain bones and teeth vitamin d is naturally created by the body through exposure to sunlight and may be recommended as a supplement for individuals with limited exposure to sunlight food supplemen