Serum lithium as a compliance marker for food and supplement intake

• Published in: The American journal of clinical nutrition 2001, Vol.73 (1), p.75-79
• Main Authors: DE ROOS, Nicole M, DE VRIES, Jeanne H. M, KATAN, Martijn B
• Format: Article
• Language: English
• Subjects: Adult; Afdeling Humane voeding; Biological and medical sciences; Biomarkers - blood; Cross-Over Studies; Dietary Supplements; Dose-Response Relationship, Drug; Eating; Feeding. Feeding behavior; Female; Fundamental and applied biological sciences. Psychology; Human Nutrition; Human Nutrition & Health; Human Nutrition (HNE); Humane Voeding; Humane Voeding & Gezondheid; Humans; Lithium; Lithium - analysis; Lithium - blood; Lithium - pharmacokinetics; Male; Medical research; Middle Aged; Nutrition; Patient Compliance; Time Factors; Vertebrates: anatomy and physiology, studies on body, several organs or systems; VLAG; Yogurt
• ISSN: 0002-9165; 1938-3207
• DOI: 10.1093/ajcn/73.1.75

Analyzing 24-h urine for lithium after consumption of lithium-tagged foods or supplements provides a validated compliance marker but is laborious. Most studies involve blood sampling; therefore, we tested whether serum lithium concentration could be used as a compliance marker. We used serum lithium as a compliance marker in a dietary trial and an evaluation study. In the dietary trial, 78 volunteers consumed 500 mL yogurt tagged with lithium (250 micromol/d) for 6 wk. Serum lithium increased from 0.9+/-0.3 to 6.6+/-1.5 micromol/L, which was close to the predicted concentration, indicating that the subjects were highly compliant. However, the interindividual variability in serum lithium concentration was large. To test whether this variability resulted from compliance differences or natural variability, we performed an evaluation study: 12 subjects took a lithium supplement (250 micromol/d) for 13 d under supervision. Serum lithium increased from 0.14+/-0.03 to 3.9+/-0.8 micromol/L (range: 2.6-5.4 micromol/L); thus, there was wide interindividual variation in serum lithium despite 100% compliance. However, within-subject variability was small, with a CV of 7% for serum lithium measured on 4 different days. We checked whether taking half the dose on each of 2 d (125 micromol lithium/d) would significantly lower serum lithium. Indeed, serum lithium dropped in all subjects, by a mean of 1.0 micromol/L on the first day (P or =1.0 micromol/L suggest altered compliance. Serum lithium concentrations after intake of lithium-tagged foods or supplements can be used to assess compliance in dietary trials.