Use of Oral Contraceptives Blunts the Calciuric Effect of Caffeine in Young Adult Women
Abstract
Caffeine consumption increases the urinary
excretion of calcium and other minerals. Factors that affect caffeine
metabolism
such as steroid hormones may modify this effect.
The purpose of this study was to evaluate the influence of oral
contraceptive
(OC) use on the 4-h urinary excretion of calcium,
phosphorus, magnesium, zinc, sodium, potassium and caffeine metabolites
in response to a high caffeine dose given as coffee
beverage. Adult women, 20–29 y, users (+OC, n = 15) and nonusers (−OC, n
= 15) of oral contraceptives, with calcium intake ∼ 500 mg/d,
participated in two tests, caffeine load (5 mg/kg body weight)
and no-caffeine control, in a randomized crossover
design. The net increase (caffeine load corrected by no caffeine) in
urinary
excretion of most minerals was significantly higher
in −OC than in +OC (P < 0.05), with the larger group
difference for calcium (ninefold) followed by magnesium (twofold), zinc
(onefold) and potassium
(onefold). Net increases in urinary excretion of
1-methylurate and paraxanthine were about three- and fivefold higher,
respectively,
in −OC than in +OC (P < 0.05) whereas
net increases in urinary excretion of
5-acetylamino-6-formylamino-3-methyluracil (AFMU) and 1,7-dimethylurate
were over twofold higher in the +OC than in −OC (P < 0.05). Following the caffeine load, most urinary minerals showed negative correlation with urinary 1-methylurate in −OC
(R ≤ −0.78, P < 0.01), and with urinary AFMU and 1,7-dimethylurate in +OC (R ≤ −0.84, P
< 0.01). Oral contraceptives appear to limit the renal effect of
caffeine on mineral excretion possibly by reducing paraxanthine
excretion, the most active caffeine metabolite.
Witma Aptriyana
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