Coffee linked to slower biological ageing among those with severe mental illness

As someone formally diagnosed with one of these mental illnesses, I can confidently say that coffee triggers a beneficial reaction to my illness as well as to other health-adjoint mechanisms in my body. To me, drinking coffee is like breathing air or eating food, and to go without it means symptom flare-ups.

Is it the coffee or caffeine in coffee? Do you feel the same benefits if you have decaffeinated coffee? Can you replace it with just caffeine pills to get same effect?

I have not tried caffeine pills myself, but I have found caffeine in general to be slightly beneficial, but with coffee having the most pronounced effect on my symptoms.