Vitamin D3 is a critical nutrient for regulating phosphorus and calcium levels in the body. This is why Vitamin D3 may be important for healthy bones, teeth and heart health. Vitamin D3 also plays a critical role in supporting a healthy immune system as well. Without it, important immune cells such as T-lymphocyte (T-cells) would not develop fully or function properly. All of these things make Vitamin D 3 especially important for older aging adults to maintain strong bones and teeth, as well as, a healthy heart and immune system. While Vitamin D is produced within our bodies, those who spend much of their time indoors may not be receiving enough sunlight for the body to produce adequate amounts of Vitamin D3. Therefore, a taking a daily supplement of Vitamin D3 may be beneficial for optimal health and wellness.