title: Effect of dietary phosphate intake on the circadian rhythm of serum phosphate concentrations in chronic kidney disease: a crossover study.
abstract: BACKGROUND
  Previous trials of binders in chronic kidney disease (CKD) stages 3-5 have shown only modest changes in serum phosphate but evaluated morning phosphate. It is unknown whether a circadian pattern of phosphate concentrations exists in CKD and is modifiable by dietary manipulation.
  
  
  OBJECTIVE
  We determined the circadian pattern of serum phosphate concentrations in CKD and whether it was modifiable by altering absorbable phosphate.
  
  
  METHODS
  This was a crossover feeding study in 11 CKD participants (estimated glomerular filtration rate: 30-45 mL · min(-1) · 1.73 m(-2)) and 4 healthy control subjects. All subjects received high-phosphate (2500 mg/d), normal-phosphate (1500 mg/d), and low-phosphate (1000 mg/d plus 1000 mg lanthanum carbonate 3 times/d) diets for 5 d followed by a 10-d washout. After each 5-d feed, phosphate and other measurements were made every 4 h over 1 day.
  
  
  RESULTS
  In CKD participants who consumed the high-phosphate diet, there were circadian changes in phosphate with lowest concentrations (± SDs) at 0800 (4.2 ± 0.5 mg/dL) and 2 peaks at 1600 and 0400 (4.5 ± 0.8 and 4.4 ± 0.6 mg/dL, respectively), which were similar to those in healthy controls. Results with the normal-phosphate diet were similar. The low-phosphate diet altered the circadian rhythm (P = 0.02) such that 0400 and 1600 peaks were absent. Differences in phosphate for lowest- compared with highest-phosphate diets were smallest at 0800 and largest at 1600 (0.5 compared with 1.0 mg/dL) in CKD. Circadian changes in phosphate were not explained by urine phosphate excretion, parathyroid hormone, or fibroblast growth factor-23.
  
  
  CONCLUSIONS
  A circadian pattern of serum phosphate is observed in CKD with lowest concentrations at 0800 and highest at 1600 and 0400. This circadian pattern is modifiable by phosphate intake and most evident at 1600. Future intervention studies targeting intestinal phosphate absorption should consider afternoon phosphate measurements.
authors.affiliation: From the Division of Nephrology, Department of Medicine (JHI) and Division of Preventive Medicine, Department of Family and Preventive Medicine, University of California San Diego, San Diego, CA (JHI and CAMA); the Nephrology Section, Veterans Affairs San Diego Healthcare System, San Diego, CA (JHI); and Denver Nephrology, Denver, CO (GS, MSP, and GAB).
authors.forename: Joachim H
authors.initials: JH
authors.lastname: Ix
authors.affiliation: From the Division of Nephrology, Department of Medicine (JHI) and Division of Preventive Medicine, Department of Family and Preventive Medicine, University of California San Diego, San Diego, CA (JHI and CAMA); the Nephrology Section, Veterans Affairs San Diego Healthcare System, San Diego, CA (JHI); and Denver Nephrology, Denver, CO (GS, MSP, and GAB).
authors.forename: Cheryl A M
authors.initials: CA
authors.lastname: Anderson
authors.affiliation: From the Division of Nephrology, Department of Medicine (JHI) and Division of Preventive Medicine, Department of Family and Preventive Medicine, University of California San Diego, San Diego, CA (JHI and CAMA); the Nephrology Section, Veterans Affairs San Diego Healthcare System, San Diego, CA (JHI); and Denver Nephrology, Denver, CO (GS, MSP, and GAB).
authors.forename: Gerard
authors.initials: G
authors.lastname: Smits
authors.affiliation: From the Division of Nephrology, Department of Medicine (JHI) and Division of Preventive Medicine, Department of Family and Preventive Medicine, University of California San Diego, San Diego, CA (JHI and CAMA); the Nephrology Section, Veterans Affairs San Diego Healthcare System, San Diego, CA (JHI); and Denver Nephrology, Denver, CO (GS, MSP, and GAB).
authors.forename: Martha S
authors.initials: MS
authors.lastname: Persky
authors.affiliation: From the Division of Nephrology, Department of Medicine (JHI) and Division of Preventive Medicine, Department of Family and Preventive Medicine, University of California San Diego, San Diego, CA (JHI and CAMA); the Nephrology Section, Veterans Affairs San Diego Healthcare System, San Diego, CA (JHI); and Denver Nephrology, Denver, CO (GS, MSP, and GAB).
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Block
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002940:Circadian Rhythm; D018592:Cross-Over Studies; D004032:Diet; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood; D005919:Glomerular Filtration Rate; D064368:Healthy Volunteers; D006801:Humans; D007811:Lanthanum; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000008:administration & dosage* / Q000097:blood*; D051436:Renal Insufficiency, Chronic / Q000097:blood*
chemical_list: D010281:Parathyroid Hormone; D010710:Phosphates; C119467:lanthanum carbonate; D005346:Fibroblast Growth Factors; D007811:Lanthanum; D000089703:Fibroblast Growth Factor-23