Recommended for people with low vitamin D levels and inadequate calcium intake. Also, those seeking a convenient combined Vitamin D & Calcium supplement. Why Ostelin Vitamin D & Calcium Ostelin Vitamin D & Calcium has the highest levels of Vitamin D & Calcium per tablet in a combination product. The Ostelin range is Halal accredited. How this product works Vitamin D is essential for calcium absorption, required for healthy bones and teeth. Calcium is essential in our youth and throughout life to maximise and strengthen bones, and may assist in the prevention and treatment of osteoporosis.