Vitamin D promotes calcium absorption, which helps to maintain healthy bones and teeth and is also useful in supporting a healthy immune system. It may also support nerve and muscle function which is particularly useful for older adults. The majority of modern adults in Ireland are deficient in Vitamin D. It is sourced mainly from sunlight, something we see very little of unfortunately. It can be difficult to source from the modern diet. It is presented in the form of Vitamin D3 in this supplement as this is the most absorbable form of the nutrient. 1000IU daily is an appropriate strength for those who are mildly deficient in this vitamin.