Liquid D3 & K2 supports normal immune function, bone maintenance, and regulates serotonin levels, the brain's 'feel-good' chemical Immune System – Contributes to the normal functioning of the immune system. Healthy Bones & Teeth – Contributes to the maintenance of normal bones and teeth. Feel Good – Vitamin D3 helps regulate serotonin levels, the brain's 'feel-good' chemical.