Interactions between dietary caffeine and calcium on calcium and bone metabolism in older women.
OBJECTIVE
Our purpose was to determine the effect of 2 weeks of caffeine abstinence on calcium (Ca) and bone metabolism in women habitually consuming caffeine and either low or moderate amounts of Ca.


METHODS
Participants were 25 women, aged 39-76 years (mean 65 years, median 57 years) habitually consuming at least 200 mg caffeine daily. Three days of dietary records and 24-hour urine collections were made immediately prior to collection of fasting blood and 1-hour urine in a metabolic unit. Women were classified as low Ca consumers (414-584 mg daily) or moderate Ca consumers (662-1357 mg daily) based on 6 days of diet records.


RESULTS
Women in the low Ca group had higher levels of serum ultrafiltrable Ca (UFCa) after caffeine abstinence (1.40 mmol/L CAF+ vs 1.52 mmol/L CAF-, p < 0.01), while there were no differences between experimental periods for UFCa in the moderate Ca group (1.35 mmol/L CAF+ vs 1.38 mmol/L CAF-, ns). Women in the low Ca group also had lower serum bone isoenzyme alkaline phosphatase levels after caffeine abstinence (9.3 U/L CAF+ vs 8.8 U/L CAF-, p < 0.05), while no significant changes were seen in bone alkaline phosphatase in the moderate Ca consumers (8.7 U/L CAF+ vs 8.9 U/L CAF-, ns). Fasting total serum Ca, urinary hydroxyproline/creatinine, and Ca/creatinine ratios were unchanged in both dietary groups. Three-day mean 24-hour urinary Ca excretion decreased after caffeine abstinence in the moderate Ca group only. There were no differences in dietary intakes of Ca from dairy products between CAF+ and CAF- in either the low or moderate Ca groups.


CONCLUSIONS
Abstinence from moderate caffeine intake (mean 5.8 mg/kg lean body mass, 383 mg/day caffeine) raises ultrafiltrable Ca and decreases bone alkaline phosphatase in older women consuming < 600 mg Ca daily.
Massey
L K
LK
Food Science and Human Nutrition Department, Washington State University, Spokane 99204-0399.
Bergman
E A
EA
Wise
K J
KJ
Sherrard
D J
DJ
D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism*; D000469:Alkaline Phosphatase / Q000032:analysis; D001842:Bone and Bones / Q000378:metabolism*; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology*; D002118:Calcium / Q000097:blood / Q000378:metabolism* / Q000652:urine; D002136:Calcium, Dietary / Q000008:administration & dosage / Q000494:pharmacology*; D003404:Creatinine / Q000097:blood; D015930:Diet Records; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005260:Female; D006801:Humans; D008875:Middle Aged; D013997:Time Factors
D002136:Calcium, Dietary; D002110:Caffeine; D003404:Creatinine; D000469:Alkaline Phosphatase; D002118:Calcium