Most urologists believe that caffeine can irritate an enlarged prostate, so it is best to limit consumption of coffee, tea, and soft drinks with caffeine.
Caffeine tends to cause the muscles in the neck of the bladder (where it enters the urethra) to tighten up, making the ability to urinate more difficult. Caffeine also acts as a diuretic, increasing the amount of urine that enters the bladder. These two factors can increase the urgency and frequency of urination, making urinary symptoms worse.
If you must have caffeine, tea -- especially green tea -- is the best choice because it contains antioxidants and is lower in caffeine than coffee and many sodas.