Zinc in Total Parenteral Nutrition. Requirements and Metabolic Effects

Abstract

Abstract Each of 24 patients with gastrointestinal disease was studied for a period of 3 wk while receiving total parenteral nutrition (TPN) to which zinc had been added in amounts of either 0.0, 1.5, and 3.0 or 6.0, 12.0, and 23.0 mg/day for each of the (three) weekly periods. Abnormal zinc excretion occurred from the gastrointestinal tract in diarrheal stools and intestinal fluids lost through suction and fistulous discharge. Gastrointestinal loss of zinc depended on the volume of the contents lost and the source of these contents. The mean concentration of zinc in gastrointestinal contents was found to be 15.2 δg of zinc/g of contents for the output from patients with an intact small bowel and 3.6 δg/g of contents from high small bowel fistulae and after extensive small bowel resection. Urinary loss of zinc occurred in all patients but constituted the major source of excretion only in patients without diarrhea or small bowel drainage. Increased urinary zinc excretion was found to occur in association with a significantly elevated urinary nitrogen. Zinc balance could be achieved only by supplying this metal in excess of obligatory losses, and a positive zinc balance was associated with improved nitrogen retention. Hence, there appeared to be a link between the metabolism of protein and that of zinc. Patients with large gastrointestinal losses of zinc were found to have significantly lower insulin and higher glucose levels (and lower lactate and pyruvate levels) than patients with normal gastrointestinal loss. Furthermore, plasma insulin increased whenever a negative zinc balance was converted to a positive one, and vice versa. These findings raise the possibility that zinc deficiency impairs insulin response and the utilization of glucose and amino acids. Appropriate zinc replacement in such patients seems, therefore, to be an important component of total parenteral nutrition. An estimate for this replacement, based on a formula developed from the authors' observations, would have placed most patients in zinc balance.