Studies of a urinary biomarker of dietary inorganic sulphur in subjects on diets containing 1-38 mmol sulphur/day and of the half-life of ingested 34SO4(2-).

OBJECTIVE: Sulphites are widely used food additives that may damage health, hence limits are set on their use. They are excreted in urine as sulphate, along with sulphate derived from sulphur amino acids. Dietary intakes of sulphites are hard to determine, so we have tested the utility of urinary nitrogen:sulphate ratio as a biomarker of inorganic sulphur (IS) intake. Additionally we determined the half-life of ingested (34)SO(4)(2-) from its urinary excretion.
SUBJECTS: Twenty healthy adult subjects were recruited by poster advertisement, for a 24-h study where they ate specified foods, which were high in IS, in addition to their normal diet. The half-life of ingested (34)SO(4)(2-) was assessed in five healthy volunteers, given 5.9 mmols of Na(2)(34)SO(4) as a single dose and collecting all urine specimens for 72-96 h. Urine and duplicate diets from three previously conducted studies were analysed for nitrogen and sulphate content, thus expanding the range of IS intakes for evaluation.
METHODS: Duplicate diets were analysed for IS content by ion exchange chromatography, while IS intake was predicted from urinary sulphate (g/day S)-(urinary nitrogen (g/day)/18.89). (32)S:(34)S ratios were determined by liquid chromatography mass spectrometry/mass spectrometry.
RESULTS: The range of IS intake was 1.3-37.5 mmol S/day. Actual and predicted IS intakes were mmol/day+/-s.e. 9.2+/-0.65 and 7.0+/-0.45, respectively, and were correlated r=0.60 (n=108). The mean half-life of ingested (34)SO(4)(2-) was 8.2 h.
CONCLUSIONS: From a 24-h urine collection, IS intake from the habitual diet can be determined for groups of individuals. To predict individual intakes of IS, which may include high sporadic amounts from beer and wine, at least 48 h of urine collection would be required.