Nature’s Bounty Vitamin D3 400IU Tablets are designed to support bone health and immune function by providing vitamin D3, the form your body naturally produces when exposed to sunlight. Vitamin D3 plays a crucial role in calcium absorption, which is essential for maintaining strong bones and teeth. It plays a crucial role in modulating the immune response, helping to defend against pathogens. Vitamin D3 supports muscle function and nerve signaling, contributing to overall neuromuscular health.