Holland & Barrett Magnesium & Zinc 90 Tablets. Magnesium contributes to a reduction of tiredness and fatigue, normal energy yielding metabolism, normal functioning of the nervous system and normal muscle function. Contributes To the Maintenance of Normal Bones Reduces Tiredness and Fatigue For veg and vegans Zinc contributes to the normal function of the immune system, normal fertility and reproduction, maintenance of normal bones and has a role in the process of cell division.