Sulfur balances in intravenously fed infants: effects of cysteine supplementation.

Sulfur balances were completed in newborn infants parenterally fed with or without cysteine. In both groups, the preservative, potassium metabisulfite, accounted for the majority of sulfur intake (32 mg S/kg/day), while methionine intakes provided an additional 27 sulfate losses accounted for approximately 95% of the sulfur excretion, with the remainder contained in amino acids. Balance data accounted for over 99% of the sulfur infused in the unsupplemented group, but only 90% of that given to the cysteine-supplemented group. Thus, urinary excretion of sulfate generally reflects input from either inorganic or amino acid sources. Of the sulfur retained in the supplemented group, 75% was calculated to be retained in lean tissue and in increases in total body sulfate, but the distribution of the remaining 25% remains unknown. The failure to account fully for the sulfate provided to the cysteine-supplemented group, however, may be due to errors in the balance technique or due to an accumulation of cysteine or sulfate in body pools undefined by this study.