I have people ask me this all the time, whether it's patients or friends & family. What is the actual deal with caffeine? It seems that people hear different answers, depending on who is asking and who is answering. So I have dug deeper to find some research-based answers. However, the caveat is that there is no single answer that fits everyone; we are all different and have differing circumstances.
So I will start with the potentially bad things related to caffeine intake:
First, it can be habit-forming, which could be a bad thing for some people (especially those with addictive tendencies).
Negative effects include anxiety, feeling jittery or restless, tremors, dizziness, fast heartbeat, dehydration, and difficulty with sleep/insomnia.
Excess consumption may also lead to irregular heartbeat, headaches/migraines, GI upset, reflux (GERD), and high blood pressure in some individuals.
Caffeine can interact with some medications, so be sure to read the information included with your prescriptions.
It can cross the placenta, so pregnant women are at an increased risk of adverse outcomes such as low birth weight or even miscarriage. It is recommended that pregnant women limit their intake to a max of 200mg per day (roughly 2 cups of coffee).
The USDA considers 400mg per day to be a safe dose for most people (although fatal overdoses have been seen with just a single 500mg dose of caffeine).
Now to the more positive effects:
Caffeine may boost metabolism and ramp up fat burning.
It seems to have a positive effect on exercise and physical performance - improving muscle contractions, increasing fatigue tolerance/endurance, and reducing the perception of exertion (meaning that workouts feel a little easier).
Caffeine does not increase the risk of heart disease, and may in fact lower the risk. Studies have shown that drinking 1-4 cups of coffee or green tea daily can diminish cardiovascular risk anywhere from 14 - 20%. Remember, though, that caffeine intake may raise blood pressure, although this effect can eventually go away with regular consumption.
Coffee consumption in general has been shown to decrease premature death as a possible longevity proponent.
Cancer risk appears to be reduced, with studies showing benefits against skin cancer, liver cancer, and colorectal cancer in daily coffee drinkers.
As a central nervous system stimulant, caffeine improves mood and boosts some aspects of brain function (including alertness, reaction times, and short-term recall). It has also been shown to decrease depression and suicide risk.
Some studies have shown an associated decrease in the risk of brain diseases like Alzheimer's & Parkinson's with coffee and tea consumption. (Coffee and tea both contain other healthy phytonutrient compounds which could be the actual beneficial ingredients.) There are even some studies suggesting a decreased risk of developing multiple sclerosis (MS), although there is conflicting research that says the opposite.
There appears to be a direct correlation between caffeine intake and lowered risk of diabetes. However, the reduced risk of diabetes was also seen with consumption of decaffeinated coffee, again indicating that the health benefit may come from other compounds in coffee.
Coffee seems to lower risk of liver disease, possibly reducing the risk of cirrhosis in susceptible people. Studies point to coffee improving treatment response in patients with liver damage, slowing the progression of liver disease, and even reducing the risk of premature death.
Regular coffee intake of 4 daily cups seems to reduce the risk of developing gout.
The interesting thing about all of this research is the possibility that the actual health benefits are from plant compounds in coffee and tea other than caffeine itself. Regardless, the data seems to point to more beneficial qualities then negative effects, especially when consumption is moderate at most.
My recommendation is to limit intake to 2 to 4 cups of coffee or tea per day, and to only 1 cup daily for pregnant women if approved by your obstetrician. If you have any of the symptoms mentioned above, decrease or stop your intake of caffeine. And again, watch out for interactions with medications.