What is Calcium Citrate?
Calcium is the most abundant mineral in the body.  Calcium is naturally found in dairy, tofu, beans, and even some vegetables.  Calcium citrate is calcium + citric acid. Chemically bonding calcium to citrate improves the bioavailability of calcium.  Regardless of the form of calcium, obtaining an adequate amount of vitamin D can increase calcium absorption in the gut. Vitamin D can also help maintain serum levels of calcium.  Consuming an adequate amount of calcium can increase bone mass density, help balance blood pressure, and can even aid fat loss efforts. [1,4,5,6,7]
Calcium Citrate VS Calcium Carbonate
While calcium carbonate is more common, calcium citrate has greater bioavailability, can have fewer gastrointestinal side effects, and can be taken at any time. 
Calcium Citrate Benefits
In the body, calcium is the building block of our bones. It also has diverse roles in cellular and hormonal signaling. Inadequate calcium intake can lead to brittle bones and hormonal imbalances. [1,6,5]
Calcium is one of the major factors in achieving optimal bone mass density (BMD).  99% of bodily calcium is found in our bones and teeth; the other 1% is found in plasma and soft tissues.  The 1% is vital to maintaining bodily homeostasis. Maintaining the right calcium levels in extracellular fluids and plasma is so vital that the body will break down its support beams (bones) to achieve the perfect balance.  Generally speaking, the body will only breakdown bones if calcium intake is not enough to meet bodily demands.
Early adolescence is the period in which the most rapid increase in bone density is seen.  After peak bone mass density is attained, the general goal is to maintain as much bone mass as possible. As previously mentioned, if calcium intake is not sufficient to support bodily functions, the body will catabolize bone to obtain calcium.  If this occurs over the course of years, or even decades, bones can become thin, brittle, or misshapen.
The cellular roles of calcium permit accelerated fat loss, secondary to proper diet and exercise. One study observed a group of participants that consumed 1,300mg of calcium per day alongside another group that consumed 488mg calcium per day. The group consuming more calcium had 11% higher fat oxidation than the low calcium group.  A long-term study found that over the course of a year, the high calcium group lost 35% more weight, relative to the low calcium group. In general, adequate calcium intake has been associated with higher rates of whole-body fat oxidation.  Increased fat burning is likely due to intracellular calcium’s regulation of fat cell metabolism, as it can act as a signal molecule. 
Calcium Citrate Powder Dosage
The recommended dosage of calcium citrate is two flat 1/8 tsp scoops (980mg) once daily.
Calcium Citrate Side Effects
Too much calcium intake may cause constipation. Using magnesium with calcium may counteract this side effect.