Dietary Supplement Essential For Strong Bones and Teeth Purity & Potency Guaranteed Natural Factors Vitamin D3 is essential for strong bones and teeth as it increases the body's absorption of calcium from food. Its role in regulating calcium levels also helps regulate the immune system and maintain healthy nerves and muscles. All Natural Factors products are manufactured in accordance with the Government of Canada's Good Manufactured Practices (GMP), among the highest standards in the world.