ossofortin Vitamin D2 for Vitamin D deficiency and muscle weakness. ossofortin is a nutritional supplement that contains Vitamin D2 (ergocalciferol), to compensate for Vitamin D deficiency in the body, and prevent osteoporosis, muscle weakness, feeling of fatigue, and constant tiredness. Vitamin D helps in the absorption of calcium, and is available in the form of tablets of 50,000 IU and 10,000 IU.