600 + D Magnesium & More. Helps reduce the risk of hip fractures by 29%. Complete Bone Health Formula With 9 Bone Health Nutrients. Gluten Free. More Nutrients than Caltrate® or Citracal® Reasons to choose Os-Cal®:. Helps reduce the risk of osteoporosis. Highly absorbable calcium. Meets USP dissolution standards. Contains the only form of calcium shown to help promote colon health. One Os-Cal Ultra® has 0 calories; one Viactiv® has 20 calories. One Os-Cal Ultra® has 600 mg of elemental calcium; one Citracal + Vitamin D® has only 315 mg.