Effect of caffeine on calcium and magnesium excretion

Nutrition Research Newsletter, Oct, 1994

The consumption of caffeine causes a short-term increase in the urinary excretion of calcium and magnesium. It is uncertain, however, whether caffeine intake leads to an increase in the excretion of these minerals over a 24-hour period. Enhanced renal conservation later in the day might be sufficient to compensate for the increased mineral loss that occurs in the first few hours after caffeine intake. This study, conducted at Washington State University, was designed to determine whether the increased calcium and magnesium excretion resulting from morning consumption of caffeine would be offset by decreased excretion later in a 24-hour cycle.

Seventeen healthy men and women, aged 17-41 years, completed a two-day metabolic ward study in which they ate a controlled diet containing 11.3 mmol Ca and 12.7 mmol Mg. On the first day, no caffeine was consumed. On the second day, two caffeine doses of 3 mg/kg lean body weight were consumed at 7:00 and 10:00 A.M. Salivary caffeine concentrations and urinary calcium, magnesium, sodium, and creatinine excretion were measured.

Urinary excretion of calcium and magnesium was significantly elevated for six hours after the second dose of caffeine. This increase was partly offset by a decrease in calcium and magnesium excretion between 1:00 and 4:00 A.M. However, the magnitude of renal conservation was insufficient to compensate completely for the caffeine-induced loss of these minerals.

The results of this study indicate that renal conservation does not fully compensate for the effect of caffeine on calcium and magnesium excretion. Regular consumption of caffeine may contribute to the causation of osteoporosis by promoting depletion of these two important minerals.

Susan A Kynast-Gales and Linda K Massey, Effect of Caffeine on Circadian Excretion of Urinary Calcium and Magnesium, J American College Nutrition 13(5):467-472 (Oct 1994) [Reprints: Linda K Massey, PhD, Food Science and Human Nutrition, Washington State University, 601 West First Avenue, Spokane WA 99204-0399]