Effect of caffeine on circadian excretion of urinary calcium and magnesium

J Am Coll Nutr. 1994 Oct;13(5):467-72. doi: 10.1080/07315724.1994.10718436.


Objective: To determine if later renal conservation occurs in calcium (Ca) and magnesium (Mg) excretion after morning caffeine-induced increases in urinary Ca and Mg excretion.

Design: Before-after trial of caffeine abstinance and consumption was conducted on two consecutive days in a metabolic ward while subjects ate a controlled diet containing 11.3 mmol Ca and 12.7 mmol Mg. 17 healthy males and females, ages 17-41 yr volunteered. Two caffeine doses of 3 mg/kg lean body mass caffeine were consumed at 7 and 10 a.m. on second day. Salivary caffeine concentrations and urinary Ca, Mg, sodium and creatinine excretion were measured.

Results: Salivary caffeine peaked at 4.7 umol/mL at 11:30 a.m. and declined with a half-life of 7.3 hours. Urinary Ca and Mg were elevated significantly (p = 0.01 and p = 0.04) for six h after the second caffeine dose. Caffeine had no significant effect on urinary calcium or magnesium excretion between 4 p.m. and 1 a.m. Between 1 and 4 a.m., urinary Ca and Mg excretion was decreased after caffeine (p = 0.04 and p = 0.01). Creatinine excretion was not different at any time.

Conclusions: Nighttime compensatory renal conservation was insufficient to offset morning caffeine-induced mineral losses, resulting in net 24-hour urinary increases of 0.32 mmol Ca and 0.16 mmol Mg.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Caffeine / administration & dosage
  • Caffeine / pharmacokinetics
  • Caffeine / pharmacology*
  • Calcium / urine*
  • Circadian Rhythm / drug effects*
  • Creatinine / urine
  • Female
  • Humans
  • Magnesium / urine*
  • Male
  • Saliva / metabolism
  • Sodium / urine


  • Caffeine
  • Sodium
  • Creatinine
  • Magnesium
  • Calcium