Holland & Barrett's Pure Cod Liver Oil is high in omega 3 fatty acids and provides an excellent source of vitamins A and D. Both Vitamins A and D contribute to the normal function of the immune system. Vitamin A also contributes to the maintenance of normal skin, whilst Vitamin D contributes to the maintenance of normal bones and muscle function. This formula contains Glucosamine which is produced naturally in the body, yet there are no major food sources of this substance. Glucosamine is a major structural component within joint tissue.