Americans love their coffee. According to a survey cited by Statista, 29% of US coffee drinkers consume two cups of coffee daily, 13% drink three cups, 14% drink four to five cups, and 9% drink more than six. All that coffee consumption equates to high energy levels—but beware, coffee lovers: Caffeine can impair absorption and facilitate excretion of certain vitamins and minerals.
The following are five nutrients that interact with caffeine.
For every cup of coffee consumed, 5 mg of calcium is excreted in urine and feces. The loss can occur several hours after caffeine intake. Furthermore, coffee likely mitigates the absorption of calcium and depletes bones of calcium.
The jury is still out on the physiologic effects of increased calcium excretion and decreased absorption secondary to caffeine intake.
According to a review article published by the Linus Pauling Institute, “there is little evidence to suggest detrimental effects of coffee on bone health in populations with adequate calcium intakes. To date, results from observational studies that examined associations between coffee intakes and measures of bone mineral density (BMD) loss—generally used to diagnose osteoporosis—have been mixed.”
Nevertheless, some research has demonstrated that at higher levels of consumption, caffeine in the form of coffee could impact osteoporosis. For example, the Linus Pauling Institute cited some subgroup analyses spanning several studies that indicated that women who drink lots of coffee exhibited a 14% increased risk of fracture and a 35% increased risk of osteoporotic fractures compared with women who drank less coffee.
Vitamin D plays a critical role in the absorption of calcium that is used to form bone. Caffeine acts as an inhibitor of vitamin D receptors, thus stymieing vitamin D absorption and possibly decreasing bone-mineral density, leading to osteoporosis
Considering the effects of caffeine on both calcium and vitamin D, the Linus Pauling Institute recommended the following: “Limiting coffee consumption to ≤3 cups/day while ensuring adequate calcium and vitamin D intakes should prevent any potential adverse effects on calcium absorption and bone health.”
Caffeine interferes with iron absorption, as phenolic compounds in coffee bind nonheme iron. This interaction could impact red blood cell production. When consumed with iron-rich foods, caffeine can decrease iron absorption by up to 80%.
Per a review article published in Food Science and Quality Management: “Any beverage containing caffeine should be separated from iron-containing foods or supplements by at least one hour.”
Caffeine is a diuretic, which means that water-soluble vitamins, including B vitamins, are flushed out with increased urination. Furthermore, caffeine interferes with the metabolism of certain B vitamins, including thiamine.
However, because caffeine increases stomach acid secretion, it actually boosts the absorption of vitamin B12. Remember that vitamin B12, or cobalamin, binds to gastric intrinsic factor (IF) secreted from gastric parietal cells; gastric IF facilitates the absorption of free cobalamin. Importantly, gastric IF levels rise with gastric acid levels. The remaining cobalamin is absorbed passively via the terminal ileum.
According to the results of a small study published in Life Sciences, women between the ages of 31 and 78 years who consumed coffee with a 6 mg/kg caffeine concentration on two separate mornings experienced urinary losses of magnesium, calcium, sodium, chloride, potassium, creatinine, and water within 2 hours of intake.
“The percent reabsorption of calcium (98.6% to 97.5%, p < 0.001) and magnesium (97.0% to 94.2%, p < 0.0001) decreased significantly during the post-caffeine period. The calcium and magnesium filtered loads did not differ significantly between the caffeine and no caffeine beverages,” the authors wrote.
They concluded: “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.”
What to do?
For coffee lovers who “need” coffee to get going in the morning (or at other times of the day), cutting out this caffeinated pick-me-up completely would be difficult. Other than reducing consumption, one workaround to the nutrient-depleting effects of coffee and other caffeinated beverages could be timing, at least according to the results of an early study published in the American Journal of Clinical Nutrition.
“When a cup of drip coffee or instant coffee was ingested with a meal composed of semipurified ingredients, absorption was reduced from 5.88% to 1.64% and 0.97%, respectively, and when the strength of the instant coffee was doubled, percentage iron absorption fell to 0.53%,” they wrote.
They added: “No decrease in iron absorption occurred when coffee was consumed 1 h before a meal, but the same degree of inhibition as with simultaneous ingestion was seen when coffee was taken 1 h later.”
So, keep an eye on your caffeine consumption (but also be aware of its many benefits).