What does caffeine do to your cells and their repair process?

Caffeine blocks two proteins that act as guardians of your DNA. These guardians normally detect damage to the DNA and force the cell to stop so there is time for repair. Caffeine switches those stop signals off, allowing a cell with damaged DNA to simply keep dividing. This has been demonstrated in cell studies and is causal: caffeine does this directly.

In addition, caffeine also inhibits the repair enzymes themselves. An enzyme that stitches broken pieces of DNA back together is directly inhibited. In bacterial studies, caffeine was also shown to make repair proteins stick to the wrong location on the DNA, preventing them from carrying out their actual task. This bacterial evidence does not automatically tell us anything about human cells, but the inhibition of the repair enzyme has also been observed in human cells.

Whether this is harmful depends strongly on context. In cancer therapy, the same mechanism is sometimes used deliberately: by switching off the stop signals of tumour cells, those cells become more sensitive to treatment with DNA-damaging agents. In healthy cells it is undesirable, but how large the risk is with normal coffee consumption cannot be stated unambiguously on the basis of the available studies.

Coffee as a drink also has another side. The plant compounds in coffee (not caffeine itself) activate a system in the cell that switches on genes for self-protection, detoxification and repair. This protective effect disappears when you take pure caffeine without those plant compounds. Furthermore, caffeine appears to be a safety signal in early pregnancy: embryological research showed rapid effects on the cardiovascular function of embryos, although the exact consequences for humans have not yet been fully investigated.