Caffeine can be present in items you never thought possible. Sodas, Chocolate, Some forms of aspirin, Certain Medication, Tea and other beverages to just name a few. Certain job functions can cause this. Typing is one such vibration that has been known to cause spasms. Usually it is caused if typing is a repetitive act you perform day after day and much of your time.
Some people do experience the spasms if they type only a few minutes.
So this is individual actually. Myself typing for long periods without short breatks in between causes me to have spasms. Workers that use power tools also are at risk. For men with raynauds this has become a bothersome fact. Many now have had to give up crafts they loved to do or they must limit the amount of time they spend on it at one sitting.