Increased calcium intake for limited periods does not normally cause toxic effects. The urine and the feces easily eliminate any excess calcium. However, an increased risk of kidney stones in persons susceptible to them has been associated with chronically high calcium intake. Low intakes of calcium for prolonged periods of time can lead to calcium deficiency. Persons with lactose intolerance have trouble digesting the sugar in milk.
Lactose intolerance is due to an inability to produce lactase, the enzyme that digests milk.
The wall of the gastrointestinal tract produces this enzyme.