There are several benefits to consuming coffee, however, the negative ramifications can often out weigh these benefits. The amount and source of caffeine consumed plays a significant role in determining this, for example brewed coffee contains the highest amount of caffeine (56-100mg/100ml) where instant coffee and tea contain less (20-73mg/100ml) . This article looks at how caffeine affects calcium absorption and bone remodelling in the body.
The consumption of four of more cups of caffeine per day has been shown to significantly increase health risks . There are acute urinary losses of calcium with the intake of caffeine [2, 3] and after fasting for 10 hours, intakes greater than 200mg (approximately one cup of brewed coffee) can increase the excretion of calcium for a further two to three hours in adults . Therefore high doses have been suggested a risk factor for osteoporosis and bone fracture [2, 4]. Additionally, it is has been suggested that calcium absorption in the gastrointestinal tract is depleted with the consumption of caffeine . A negative calcium balance can result from these mechanisms; potentially leading to premature bone loss, particularly if caffeine intake is high and calcium consumption and absorption is low . The Hallstrom et al. study concluded that the ingestion of 4 cups of coffee per day, particularly in those with low calcium intake, significantly increased the risk of osteoporotic fractures. This same study states that one glass of milk can offset the negative ramifications of two cups of coffee on bone density . However, a study conducted on healthy premenopausal women aged between 35 – 44 years showed changes to bone remodelling when at least 400mg/day of caffeine (the equivalent of approximately two cups of brewed coffee) over a 19-day period were consumed. Though this displayed no effects on calcium absorption or urinary/fecal calcium excretion .
The evidence is somewhat conflicting, although it can be said that high caffeine consumption when coupled with low calcium intake can induce negative effects on bone health.
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Anupam, R., & Biswajit, D. (2015). Effects of caffeine on health: A review. Research Journal of Pharmacy and Technology, 8 (9), 1312-1319. https://doi.org/10.5958/0974-360X.2015.00237.1
Hallstrom, H., Wolk, A., Glynn, A., & Michaelsson, K. (2006). Coffee, tea and caffeine consumption in relation to osteopororitc fracture risk in a cohort of Swedish women. Osteoporosis International, 17, 1055-1064. https://doi.org/10.1007/s00198-006-0109-y
Lacerda, S. A., Matuoka, R. I., Macedo, R. M., Petenusci, S. O., Campos, A. A., & Brentegani, L. G. (2010). Bone quality associated with daily intake of coffee: A biochemical, radiographic and histometric study. Brazilian Dental Journal, 21 (3), 199-204. Retrieved from http://www.scielo.br/pdf/bdj/v21n3/v21n3a04.pdf