INTERACTIONS BETWEEN DIETARY CAFFEINE AND CALCIUM ON CALCIUM AND BONEMETABOLISM IN OLDER WOMEN

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.