Opti-Cal/Mag Extra Strength 2:1 contains elemental calcium in a highly absorbable "bisglycinate" form, which is 180% more absorbable than common citrate forms. Zinc, vitamin D3 and digestive aids increase the effectiveness of this formula. Plus, added key nutrients protect calcium from interrupted absorption. Beneficial for individuals who avoid processed foods, eat some meat, little or no dairy and include more whole grains, nuts and vegetables into their diet.