I too have very low vitamin D level and calcium. 6 months ago a Rhuematologist explained to me why I needed a prescription for Vitamin D with 50,000 eug’s and not just an over the counter vitamin. She explained that for some unknown reason my body was not absorbing and retaining the daily recommended amount, and unless I took this supplement my osteoarthritis and osteopenia would continue to increase. I would like to add this, along with some lifestyle changes and only taking this supplement much of my chronic pain has dissipated. I make sure I get the recommended sun exposure, using a protective SPF that has UVA/ UVB protection, and I eat a plant based diet almost daily.