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.

Stability of vitamins A, C, and E, carotenoids, lipids, and testosterone in whole blood stored at 4 degrees C for 6 and 24 hours before separation of serum and plasma.

To investigate whether overnight storage causes significant changes in whole blood, we measured serum and plasma concentrations of vitamins A, C, and E, carotenoids, lipids, and testosterone in whole blood samples stored in a refrigerator at 4 degrees C for 6 and 24 h before centrifugation, aliquoting and freezing them at -70 degrees C or below. In comparison with baseline samples prepared within 2 h, the mean percentage changes at 24 h were: -3.0% to +1.0% for retinol, alpha-tocopherol, and gamma-tocopherol in plasma; -8.7% to -0.1% for carotenoids in plasma; -7.2% for vitamin C in plasma and -1.8% for vitamin C in serum; -2.7% to +2.4% for lipids in serum; and +0.4% to +6.2% for testosterone in serum and plasma from men and women. Spearman's rank correlation coefficients between measurements made in the baseline samples and those made after storage for 24 h were greater than 0.9 for 11 analytes, between 0.8 and 0.9 for 7 analytes, and less than 0.8 for only 1 analyte (vitamin C in serum). The ratio of between-subject to within-subject coefficients of variation was greater than 3.0 for all analytes except lutein (ratio, 1.6), alpha-cryptoxanthin (ratio, 2.4) and vitamin C (ratio in serum, 3.0; ratio in plasma, 2.2). We conclude that storage of whole blood at 4 degrees C for 24 h before freezing does not cause important changes in the analytes studied and that this delay in processing may be incorporated in the design of large prospective studies.