Lk. Massey et al., INTERACTIONS BETWEEN DIETARY CAFFEINE AND CALCIUM ON CALCIUM AND BONEMETABOLISM IN OLDER WOMEN, Journal of the American College of Nutrition, 13(6), 1994, pp. 592-596
Objective: Our purpose was to determine the effect of 2 weeks of caffe
ine 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 5
7 years) habitually consuming at least 200 mg caffeine daily. Three da
ys of dietary records and 24-hour urine collections were made immediat
ely prior to collection of fasting blood and 1-hour urine in a metabol
ic 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 r
ecords. Results: Women in the low Ca group had higher levels of serum
ultrafiltrable Ca (UFCa) after caffeine abstinence (1.40 mmol/L CAF+ v
s 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 CA
F+ vs 1.38 mmol/L CAF-, ns). Women in the low Ca group also had lower
serum bone isoenzyme alkaline phosphatase levels after caffeine abstin
ence (9.3 U/L CAF+ vs 8.8 U/L CAF-, p <0.05), while no significant cha
nges were seen in bone alkaline phosphatase in the moderate Ca consume
rs (8.7 U/L CAF+ vs 8.9 U/L CAF-, ns). Pasting total serum Ca, urinary
hydroxyproline/creatinine, and Ca/ creatinine ratios were unchanged i
n both dietary groups. Three-day mean 24-hour urinary Ca excretion dec
reased after caffeine abstinence in the moderate Ca group only. There
were no differences in dietary intakes of Ca from dairy products betwe
en CAF+ and CAF- in either the low or moderate Ca groups. Conclusion:
Abstinence from moderate caffeine intake (mean 5.8 mg/kg lean body mas
s, 383 mg/day caffeine) raises ultrafiltrable Ca and decreases bone al
kaline phosphatase in older women consuming <600 mg Ca daily.