Effects of dietary caffeine on renal handling of minerals in adult women.
Level 3 - non-randomized controlled study
Controlled crossover intervention study (randomization not specified in abstract)
PubMed 2402180 · doi:10.1016/0024-3205(90)90616-y
What was done
Thirty-seven women aged 31 to 78 years were evaluated on two separate mornings after consuming a decaffeinated beverage containing either 6 mg caffeine per kg lean body mass or no caffeine. Urinary excretion of water, creatinine, calcium, magnesium, sodium, chloride, and potassium, along with glomerular filtered loads and percent tubular reabsorption, were measured across the two hours post-ingestion.
What was found
Caffeine increased total two-hour urinary output of water, creatinine, potassium, and all minerals compared to the control beverage. Urinary mineral-to-creatinine ratios (mg/g) rose following caffeine: calcium increased from 120 to 200, magnesium from 70 to 110, sodium from 3,800 to 6,200, and chloride from 9,200 to 14,800. Creatinine clearance and the filtered loads of calcium and magnesium showed no significant changes. Percent renal reabsorption decreased significantly for calcium (from 98.6% to 97.5%, p < 0.001) and magnesium (from 97.0% to 94.2%, p < 0.0001).
Why it matters
This study shows that acute caffeine-induced calcium and magnesium wasting is driven by decreased renal tubular reabsorption rather than changes in glomerular filtration or filtered load.
Limits
The study was limited to an acute two-hour monitoring period in 37 women, without assessing 24-hour balance or long-term adaptation. Specific nephron segments and molecular mechanisms were not identified, and the abstract does not state whether beverage administration was randomized or blinded.
Cited by
- context Caffeine intake inhibits the absorption of minerals, particularly magnesium.