OstroVit Vitamin D3 4000 IU + K2 - 100 Tablets. Why Choose OstroVit Vitamin D3 + K2?. High Potency: Each tablet contains 4000 IU of Vitamin D3 and 100 ?. g of Vitamin K2. Vitamin D3, also known as cholecalciferol, is a fat-soluble vitamin essential for bone mineralization and immune health.