Contribution of dietary protein and inorganic sulfur to urinary sulfate: toward a biomarker of inorganic sulfur intake.
BACKGROUND
Sulfiting agents are widely used as food additives. Limits are set on their use in foods because they may adversely affect health. Sulfiting agents are excreted in urine as sulfate, which is indistinguishable from sulfate derived from sulfur amino acids.


OBJECTIVE
The objective was to assess the contribution of inorganic sulfur to urinary sulfate excretion and of dietary protein to urinary sulfate and nitrogen excretion with the aim of developing a urinary biomarker of inorganic sulfur intake.


METHODS
Nine healthy men were fed a sequence of 3 diets for 15 d (n = 7), 5 diets for 10 d (n = 6), or both. The diets contained 51-212 g protein/d (0.43-1.71 g S/d) and 0.17-0.27 g inorganic S/d; p-aminobenzoic acid-validated 24-h urine samples (n = 47) were analyzed for sulfate and nitrogen.


RESULTS
Dietary inorganic sulfur was efficiently excreted as sulfate in urine. Urinary sulfate derived from protein correlated strongly (r(2) = 0.86) with urinary nitrogen. Urinary recovery of protein sulfur and nitrogen decreased from 84% at average protein intakes (72 g/d) to 70% at high protein intakes (212 g/d). The nitrogen:sulfur ratio (in g) of the protein in the study diets was 18.9, which was maintained in urine (18.4 +/- 0.1) after dietary inorganic sulfur intake was subtracted from urinary sulfate. Therefore, inorganic sulfur intake (g/d) = urinary sulfur (g/d) - 0.054 x urinary nitrogen (g/d). For typical UK intakes of inorganic sulfur (0.25 g/d), this biomarker should produce mean (+/- SD) values of 0.24 +/- 0.10 g S/d.


CONCLUSIONS
Twenty-four-hour urinary nitrogen and sulfate values can be used to predict inorganic sulfur intake.
Magee
Elizabeth A
EA
Department of Molecular and Cellular Pathology, Ninewells Hospital and Medical School, Dundee, United Kingdom. e.magee@dundee.ac.uk
Curno
Richard
R
Edmond
Laurie M
LM
Cummings
John H
JH
D000328:Adult; D000603:Amino Acids, Sulfur / Q000378:metabolism; D015415:Biomarkers / Q000652:urine; D018592:Cross-Over Studies; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism*; D004311:Double-Blind Method; D005243:Feces / Q000737:chemistry; D005503:Food Additives; D006801:Humans; D008297:Male; D008875:Middle Aged; D009584:Nitrogen / Q000652:urine; D013431:Sulfates / Q000032:analysis / Q000652:urine*; D013440:Sulfides / Q000032:analysis; D013455:Sulfur / Q000008:administration & dosage* / Q000378:metabolism / Q000493:pharmacokinetics
D000603:Amino Acids, Sulfur; D015415:Biomarkers; D004044:Dietary Proteins; D005503:Food Additives; D013431:Sulfates; D013440:Sulfides; D013455:Sulfur; D009584:Nitrogen