People should avoid taking the antacid calcium carbonate in doses larger than half a gram, for despite its capacity to neutralize stomach acids, calcium carbonate can increase the calcium level in the blood and thus impair kidney function
Moreover, just half a gram of it can stimulate the production of gastrin, a stomach hormone that triggers acid secretion
People who avoid taking more than half a gram of calcium carbonate are less likely than average to suffer from impaired kidney function.