Best Form of Calcium Supplement

With so many options, what is the best form of Calcium?  To start, it is important to know that calcium is best absorbed in an acidic medium, hence best utilized, generally, when taken with food.  In addition, calcium can compete for absorption with other minerals such as iron, zinc and copper which are normally taken in smaller amounts.  Calcium should be taken at a separate time of day from a multi with minerals, or the large amount of calcium will potentially interfere with utilization of the iron, zinc and copper.  Some calcium supplements may include zinc, but these wouldn’t be my first choice for calcium.  The small amounts of calcium included in multis isn’t enough to worry about since usually it’s only about 100 to 200 mgs.  Fiber supplements should be taken at a different time of day then minerals, since the fiber may bind minerals in insoluble complexes and interfere with absorption and utilization.
 
Below is a listing of all the forms and what their strengths and weaknesses:

Calcium Citrate has the advantage of being mildly acidic in nature (derived from Citric Acid); this acidity enhances absorption, even when taken without food. 

Hydroxyapatite includes both calcium and phosphorus in a two to one ratio; calcium and phosphorus compete for absorption, so, if dietary intake is skewed from the one to one ratio of the two required (1000 mgs of each per day), the phosphorus may hinder calcium absorption.  Those with very high protein intake, as well as those with liberal intake of carbonated beverages like soda may have high enough phosphorus already that additional phosphorus with the calcium is not desirable.

Aquamin is well-utilized and is appropriate for individuals who want a plant-based calcium.  It tends to be quite a bit more expensive than other calcium forms.

Coral calcium is fine for absorption, but it is sometimes overpriced for benefits given.  Trace minerals in a mined form of coral calcium would probably not be as high as in a marine-grade coral because of leaching of minerals from environmental exposure.

Calcium carbonate has the advantage of high milligrams per pill since it’s 40% calcium by weight (higher percent than other forms).  It’s not as well absorbed, especially if an individual has low stomach acidity anyway or is taking an acid blocker.  Calcium carbonate is alkaline (basic) in nature - think similar to antacids.