Calcium deficiency can be caused by:
- Low calcium intakes, due to unavailability or avoidance of certain food groups, e.g. cow’s milk and other dairy produce made from cow’s milk;
Impaired intestinal calcium absorption due to interactions between the calcium content of foods and dietary phytates or oxalates (see above);
- Low calcium absorption, due to increasing age , physiological disorders such as hypochlorhydria (11), or vitamin D receptor disorder in the gut (12);
Increased calcium excretion due to elevated protein or sodium intakes (12).
Severe hypocalcaemia (serum calcium <1.9 mmol/L) is a rare phenomenon that may cause cardiac arrhythmias leading to emergency hospital admission (13). It is not typically linked to dietary intakes (unless in the severely malnourished); instead the most likely causes are hypoparathyroidism, chronic kidney disease and vitamin D deficiency (13, 14), or malabsorption e.g. in coeliac disease and/or in particular, where malabsorption of vitamin D is concomitant (14).
In healthy populations, a lower calcium absorption will usually be met with a lower urinary calcium excretion, thereby maintaining calcium homeostasis. In the case of mild calcium deficiency, study results reporting on the health benefits of calcium supplementation that are often reported in the media, were found by a thorough review by the Institute of Medicine to be mixed and inconclusive (7).
Very low calcium intakes are also associated with non-infantile rickets, either alone or together with low, but not necessarily deficient, vitamin D status (15).