Too much caffeine may be bad for bone health because it can deplete calcium. Overdoing the caffeine also may affect the vitamin D in your body, which plays a critical role in your body's bone metabolism. However, the roles of vitamin D as well as caffeine in the development of osteoporosis continue to be a source of debate.
Caffeine may interfere with your body's metabolism of vitamin D, according to a 2007 "Journal of Steroid Biochemistry & Molecular Biology" study. You have vitamin D receptors, or VDRs, in your osteoblast cells. These large cells are responsible for the mineralization and synthesis of bone in your body. They create a sheet on the surface of your bones. The D receptors are nuclear hormone receptors that control the action of vitamin D-3 by controlling hormone-sensitive gene expression. These receptors are critical to good bone health. For example, a vitamin D metabolism disorder in which these receptors don't work properly causes rickets.
The interference with vitamin D metabolism appears to be dose-dependent, meaning more caffeine has stronger effects, notes Prema B. Rapuri, lead author for the "Journal of Steroid Biochemistry & Molecular Biology" study. This effect may be one of the molecular mechanisms that helps explain caffeine's role in a raised risk for osteoporosis, according to Rapuri. However, this study was done in a laboratory, so more research is needed to determine the actual effects in your body. Consuming more than 300 mg of caffeine daily appears to accelerate bone loss among elderly women, raising risk for osteoporosis, according to a November 2001 study in "The American Journal of Clinical Nutrition." This conclusion is based on data culled from a longitudinal study and a cross-sectional study examining caffeine intake and bone mineral density in elderly women.
The risk for a negative effect of caffeine on your bone density appears to be raised when you have the TaqI, or tt, genetic variant of VDR, according to Rapuri, also the lead author for "The American Journal of Clinical Nutrition" study. This is a genetic factor that's involved in regulating cell growth in your body. Other variants of VDR include the polyA, or short short, variant; the BsmI, or BB, variant; and the Fokl variant. Such variants are implicated in risk for a variety of health issues, from bone health to risk for colon cancer.
Just how much effect caffeine has on skeletal metabolism is still a source of debate, according to "Principles and Practice of Endocrinology and Metabolism," by Kenneth L. Becker. Demonstrating a strong link between caffeine intake and bone problems like raised fracture risk is difficult due to difficulty in determining true caffeine intake levels and also due to other risk factors that exist, such as phosphorus intake from cola drinks and alcohol intake, Becker notes. Lifestyle factors, like smoking and amount of exercise, also come into play.
- “Journal of Steroid Biochemistry & Molecular Biology”; Caffeine Decreases Vitamin D Receptor Protein Expression and 1,25(OH)2D3 Stimulated Alkaline Phosphatase Activity in Human Osteoblast Cells; Prema B. Rapuri, et al.; 2007
- AbCam.com: Vitamin D Receptor Protein
- Encyclopedia Britannica Online: Osteoblast
- “The American Journal of Clinical Nutrition”; Caffeine Intake Increases the Rate of Bone Loss in Elderly Women and Interacts With Vitamin D Receptor Genotypes; Prema B. Rapuri, et al.; November 2001
- “Cancer Causes and Control”; Variants of the VDR Gene and Risk of Colon Cancer (United States); M.L. Slatter, et al.; May 2001
- “Principles and Practice of Endocrinology and Metabolism”; Kenneth L. Becker; 2001