This is really a question of your acidic food consumption and your caffeine intake in other areas.
Women who are pregnant are told not to have more than 200mg per day. (http://www.babycenter.com/0_caffeine-during-pregna...
According to http://www.espressoguy.com/coffee_beans/caffeine the amount of caffeine in an espresso shot is about 100 mg, and about 130 mg in an 8 0z cup of coffee.
On a side note the guy also states that the amount of caffeine to kill a person is "10 grams of caffeine or more (around 100 cups of coffee) to kill a healthy adult."
Caffeine is a stimulant, and since the Gastrointestinal Tract has as many neurons as the human brain (I learned this in PsyB105 at IUPUI, but here is a link http://www.psyking.net/id36.htm), it is affected by the caffeine as well. It is suggested that too much of any neurotoxin in the intestines can cause emotional symptoms, and conversely that any neural medications will cause gastro-intestinal reactions. Funny, huh?