Linda K. Massey

The effect of dietary caffeine on urinary excretion of calcium, magnesium, sodium and potassium in healthy young females

Abstract Twelve female college students drank decaffeinated coffee or tea to which 0, 150 or 300 mg caffeine had been added. Each subject had fasted at least ten hours before drinking each of the three test beverages. Urine samples were collected at one, two and three hours after caffeine consumption. Total urinary three hour excretion of calcium, magnesium and sodium, but not potassium, increased significantly after caffeine intake. The increased output of calcium and sodium was mainly due to significantly increased urinary calcium and sodium concentrations, while the increased output of magnesium appeared to be due to the combination of both a slightly increased urinary magnesium concentration and volume. Total urine volume correlated significantly with dose of caffeine per body weight when 300 mg of caffeine was consumed. The effects of caffeine on mineral excretion were primarily due to changes in mineral concentration and increased urinary volume at one and two hours.

Effects of dietary caffeine on renal handling of minerals in adult women

Thirty-seven women, aged 31-78 years, on two separate mornings consumed a decaffeinated beverage to which 6 mg caffeine/kg lean body mass or no caffeine were added. Total urine output of water, calcium, magnesium, sodium, chloride, potassium and creatinine increased in the two hours following caffeine ingestion when compared to the control beverage. Increased urinary mineral (mg)/urinary creatinine (g) ratios were seen for calcium (120 to 200), magnesium (70 to 110), sodium (3,800 to 6,200) and chloride (9,200 to 14,800), following the caffeinated beverage. Creatinine clearance did not change significantly. The percent reabsorption of calcium (98.6% to 97.5%, p less than .001) and magnesium (97.0% to 94.2%, p less than .0001) decreased significantly during the post-caffeine period. The calcium and magnesium filtered loads did not differ significantly between the caffeine and no caffeine beverages. Therefore, caffeine-induced urinary loss of calcium and magnesium is largely attributable to a reduction in calcium and magnesium renal reabsorption, although the physiological mechanism and tubular segment affected remain to be established.

Caffeine and the Elderly

The most common source of dietary caffeine among the elderly is coffee, with consumption averaging about 200 mg/day. Because of the greater proportion of adipose tissue to lean body mass in older humans, and because caffeine is distributed essentially only through lean body mass, a dose of caffeine expressed as mg/kg total bodyweight may result in a higher plasma and tissue concentration in elderly compared with younger individuals. The metabolism of, and physiological responses to, caffeine is similar in elderly and younger individuals. However, there is a limited amount of evidence that responses to caffeine in some physiological systems may be greater in the elderly at doses in the 200 to 300mg range.Although caffeine consumption increases urinary calcium levels similarly in both younger and older individuals, the preponderance of data suggest that caffeine has a greater impact on calcium metabolism and bone in older people. Evidence also suggests that increasing age is associated with increasing sensitivity to the pressor effects of caffeine. Caffeine appears to affect metabolic and neurological responses similarly in both young and elderly individuals, when differences in baseline performance are taken into account.

The effect of dietary caffeine on urinary excretion of calcium, magnesium, phosphorus, sodium, potassium, chloride and zinc in healthy males

Abstract Fifteen males drank decaffeinated coffee to which 0, 150 or 300 mg caffeine had been added. Each subject had fasted at least ten hours before drinking each of the three test beverages. Urine samples were collected at one, two and three hours after caffeine consumption. Total urinary three hour excretion of calcium, magnesium, sodium and chloride increased significantly after caffeine intake, while zinc, phosphorus, potassium, creatinine and volume were unchanged. The increased outputs were due to increased urinary mineral concentrations.

Acute effects of dietary caffeine and aspirin on urinary mineral excretion in pre- and postmenopausal women

Abstract Thirty women, ages 35–65, on three separate mornings, drank 180 ml decaffeinated coffee to which 0, 3 or 6 mg/kg body weight caffeine had been added. Caffeine increased three hour total urinary calcium excretion from a baseline value of 10.8 to 15.9 and 17.8 mg, respectively. Sodium and magnesium excretion were also increased after caffeine ingestion. Phosphorus, chloride, potassium, creatinine and urine volume were not different after caffeine consumption. Increased urinary outputs of calcium and sodium were due to the increased urinary concentrations of calcium and sodium after caffeine consumption. Twenty of these women also took 650 mg aspirin 10 hours and 1 hour before consuming a second set of beverages containing 0 and 3 mg/kg body weight caffeine. Aspirin preloading did not affect the three hour total excretion or mineral/creatinine ratio of any of the minerals measured. There were no aspirin-caffeine interactions, indicating that the caffeine effect on mineral excretion may not be mediated by prostaglandin production. Estrogen use or menopausal status had no effect on calcium excretion after caffeine or aspirin.

Substituting milk for apple juice does not increase kidney stone risk in most normocalciuric adults who form calcium oxalate stones

OBJECTIVE Increasing intake of dietary calcium from less than 400 mg to 800 mg daily may decrease the absorption of dietary oxalate, which in turn would decrease urinary oxalate excretion. The effect of substituting milk for apple juice on urine composition and risk of calcium oxalate precipitability was studied. SUBJECTS Twenty-one normocalciuric adults with a history of at least 1 calcium oxalate stone and urinary oxalate excretion exceeding 275 micromol/day on their self-selected diet. DESIGN Randomized crossover trial. INTERVENTION Each participant consumed two moderate-oxalate (2,011 micromol/day) study diets, which were identical except that one contained 360 mL milk and the other contained 540 mL apple juice as the beverage with meals. SETTING Four days free-living then 2 days in the metabolic unit of a university nutrition department. MAIN OUTCOME MEASURE Tiselius risk index for calcium oxalate precipitability calculated from urine composition. STATISTICAL ANALYSES Paired t tests. RESULTS Twenty-four hour urinary oxalate excretion was 18% lower (P<.0001) on the milk diet vs the juice diet: 423 vs 514 micromol, respectively. Calcium excretion was 17% higher (P<.05) on the milk vs juice diet: 4.7 vs 3.9 mmol, respectively. Urinary magnesium and citrate excretion, volume, and Tiselius risk index did not differ between diets. APPLICATIONS Substituting 360 mL milk daily for apple juice with meals in a diet containing moderate amounts of dietary oxalate from whole grains, legumes, fruits, and vegetables does not increase the risk index of calcium oxalate precipitability in most normocalciuric adults who form stones.

No effects of adaptation to dietary caffeine on calcium excretion in young women

Abstract Seventeen young women aged 24.4±3.8 years abstained from dietary methylxanthines for 3 weeks. Two urine collections were made on day 7 of each week: 1 hour after drinking 120 ml water, then 2 hours after 240 ml decaffeinated beverage. During the control week subjects had no caffeine during the week or day 7. For the “abstention” week no caffeine was consumed during the week then 6 mg caffeine per kg lean body mass (LBM) was consumed on day 7 in the second beverage. During an “adaptation” week subjects consumed 300 mg caffeine daily, then on day 7, 6 mg caffeine/kg LBM was consumed. After both abstention and adaptation weeks, addition of caffeine significantly increased excretion from 2.9 to 6.7 mg Ca/hr (p

Caffeine does not cause in vitro calcium loss from neonatal mouse calvaria

SummaryCalcium concentration of media containing calvaria from 6-day-old mice were unchanged by four doses of caffeine in a 48-hourin vitro system. The caffeine-treated calvaria were similar morphologically at all levels when compared to their littermate controls. In the culture conditions used, caffeine does not stimulate bone to release calcium.

Effects of acute caffeine ingestion and menopause on sulfate homeostasis in women

Inorganic sulfate is a physiological anion which is utilized in the metabolism of both endogenous compounds and xenobiotics. Its homeostasis is maintained predominantly by facilitated reabsorptive processes in the kidneys. The objectives of the present investigation were to evaluate the effects of menopausal status and caffeine ingestion on the serum concentrations and clearance of inorganic sulfate. Thirty-nine women who were classified as premenopausal, postmenopausal with or without estrogen treatment, and postmenopausal with osteoporosis participated in the study. The women were studied on two separate occasions following the ingestion of a decaffeinated beverage to which 6 mg caffeine/kg lean body mass or no caffeine was added. All women were habitual caffeine users (mean ingestion of 588 mg caffeine per day) but abstained from all caffeine sources for 2 weeks prior to the control study day. Postmenopausal women with estrogen supplementation exhibited significantly lower sulfate serum concentrations (0.24 +/- 0.02 mM vs. 0.32 +/- 0.04 mM in premenopausal women, mean +/- SD, p < 0.05) and a decreased renal reabsorption of sulfate for the control (no caffeine) period. There was no difference in serum sulfate or sulfate reabsorption in estrogen supplemented postmenopausal women, compared with women not taking estrogen. Postmenopausal women with osteoporosis had significantly lower creatinine and sulfate clearances than postmenopausal women with estrogen supplementation which may be related to their older age, or factors related to the disease process. The 6 mg/kg dose of caffeine caused a diuresis, but no change in GFR, as indicated by urine volume and creatinine clearance values, respectively. Caffeine administration resulted in an increase in the sulfate excretion rate; there was no change in sulfate serum concentrations. The results of this investigation indicate that menopause results in decreased sulfate serum concentrations that may be the consequence of a decreased renal reabsorption of sulfate. Secondly, this investigation demonstrated that caffeine ingestion increases the urinary excretion of sulfate, an effect that may be related to the diuretic effect of caffeine or due to a caffeine-induced alteration in the renal reabsorption of sulfate.

Urinary oxalate is not increased by vitamin B-6 depletion in young women

Although acute vitamin B-6 deficiency increases urinary oxalate excretion, the effects of marginal vitamin B-6 status are unknown. Mild vitamin B-6 depletion was induced in eight healthy young women by feeding a low vitamin B-6 lacto-ovo-vegetarian natural foods diet for 27 days. The basal diet contained 0.45 mg vitamin B-6 and 1.55 g/kg body weight protein. Although measures of vitamin B-6 status indicated that the women had marginal vitamin B-6 status, no effect was seen on 24 hour urinary oxalate. The women were then repleted with 1.26 mg vitamin B-6 for 21 days, followed by repletion with 1.66 mg for 21 days, then 2.06 mg vitamin B-6 for an additional 14 days. At the end of the 56 day repletion period, 24 hour urinary oxalate was unchanged from either adjustment or depletion values. Vitamin B-6 depletion associated with consumption of a low vitamin B-6 diet did not affect 24 hour urinary oxalate. Marginal vitamin B-6 status is unlikely to be a cause of calcium oxalate kidney stones in a young healthy population.