Vitamin D3 is an essential nutrient that many people in the UK are lacking due to lack of sunshine during parts of the year. But, what are the benefits of vitamin D3? Vitamin D contributes to the normal functioning of the immune system and the maintenance of normal teeth and bones for optimum bones and joint health. As it can help to support normal muscle functioning and plays a role in how well our bodies absorb calcium, vitamin D is essential to overall wellbeing.