It's everything really. Sleep, stress, blood sugar (around 80 is good), proper water intake, a lower carb diet with plenty of protein and saturated fats and cruciferous vegetables (if that is the right diet for you), walking in nature and walking barefoot in the morning sun (mitochondria as mentioned before by LizaJane) the right supplements, being happy, sometimes a lifestyle change.

A good deal of disease is probably generated by our habits and most "disease processes" can be affected by the change of habit and attitude and even if they cannot be "cured" they can be greatly improved or managed.