They have poorly absorbable vitamin B6, and the phytate levels in grains impairs the absorption of most of the divalent minerals. Excessive consumption of cereal grains are associated with a wide variety of health problems. In animal models, rickets are routinely induced by feeding them high levels of cereal grains. It is thought that the high levels of phytate in unleavened whole grain breads cause a zinc deficiency which in turn is responsible for hypogonadal dwarfism, along with other health problems associated with zinc deficiencies. In Europe, where immigrant Pakistanis consume high levels of unleavened whole grain breads, rickets among their children remains a problem.
Cereal grains seem to have a simultaneous influence on vitamin D and Ca metabolism.
Epidemiological studies of populations consuming high levels of unleavened whole grain breads show vitamin D deficiency to be widespread. The mechanism by which cereal grain consumption influences vitamin D is unclear. Some investigators have suggested that cereal grains may interfere with the enterohepatic circulation of vitamin D or its metabolites, whereas others have shown that calcium deficiency increases that rate of inactivation of vitamin D in the liver. A new mechanism for induced vitamin deficiency in calcium deprivation. High prevalence of rickets in infants on macrobiotic diets.