In a new Harvard study, it has discovered a high incidence of vision problems among men and women who drank three or more cups of coffee a day[6].  In another news headline, it says that chugging a coffee after a fatty meal of fast food can spike blood sugar in a healthy person to a level similar to those at risk of diabetes.[7] However, the latest headline is the most alarming one which says that "A 16-year-old boy died from a caffeine overdose after drinking caffeine-laden soft drinks, coffee and an energy drink."[19]

In [1], Dr. Amen warns us that drinking too much caffeine can cause the following problems:

1. Caffeine restricts blood flow to the brain

2. Caffeine dehydrates the brain

   • Caffeine has a diuretic effect on the body, including brain

3. Caffeine interferes with sleep

   • Caffeine blocks adenosine, a chemical that tells us when it is time to go to bed.

   • Caffeine's principal mode of action is as an antagonist of adenosine receptors in the brain.

4. Caffeine can be addictive in high amounts

5. Caffeine can accelerate heart rate and raise blood pressure

6. Caffeine can leave you feeling jittery and nervous

7. Caffeine increases muscle tension

8. Caffeine can cause an upset stomach[14]

9. Caffeine can elevate inflammatory markers

   • Two studies showed that 200 mg of caffeine raised homocysteine levels, a marker for inflammation and heart disease.

10. Caffeine can interfere with fertility

    • Pregnant women should be careful with caffeine because it has been associated with premature births, birth defects, inability to conceive, low birth weight, and miscarriage.

11. Caffeine can trigger migraines (other known triggers include chocolate, cheese, and MSG)[3]

But, how much caffeine is too much?  These are what experts said:

• Mayo Clinic[8,10]

  • For most healthy adults, moderate doses of caffeine — 200 to 300 milligrams (mg), or about two to four cups of brewed coffee a day — aren't harmful.  However, if you consume more than 500 to 600 mg a day, it's considered too much.

• Johns Hopkins University [9]

  • Researchers suggested that 200mg of coffee is beneficial to those who do not regularly ingest caffeine. But, they also found an inverted U-shape dose response suggesting that higher doses may not be as beneficial.

1. Caffeine can be found in lots of foods and drinks such as tea (i.e., theophylline; a molecule that is very similar to caffeine), dark sodas, chocolate (i.e., theobromine), energy drinks, and pep pills.  If your caffeine intake is limited to one or two normal-size cups of coffee or two or three cups of tea a day, it probably is not a problem.

2. Caffeine can stay in your system about 12 hours.  So, drink it in the morning hours when there is no chance that the caffeine will interfere with the sleep.

   • Caffeine's half-life is 3 to 7 hours in adults,[11] which means that six hours after you've drunk your last cup of coffee, half the caffeine remains in your system; six hours after that, a quarter is still left[2].

     • Certain conditions, such as pregnancy, prolong that half-life even further, extending it to as much as 18 hours.

     • Taking birth control pills extends the half-life of caffeine to more than 12 hours.

     • Many medications prolong caffeine's half-life as well, including the antibiotics Cipro and Levaquin, the antacid Tagamet, the antidepressant Luvox, the asthma medicine Zyflo, and the HIV drug Reyataz, to name just a few.

     • Even grapefruit juice and green tea significantly prolong the effects of caffeine in the body.

3. If you drink tea, consider this:

   • Caffeine level is highest in black tea, intermediate in oolong, and lowest in green tea.

4. If you have osteoporosis, limit your caffeine intake.  Caffeine increases the amount of calcium excreted in the urine.

5. If you have arthritis pain, avoid diuretic foods which include caffeine.

6. If you're looking for smoother and younger-looking skin, limit caffeine intake.[17,18]

   • Alcohol and caffeine ... act like a diuretic and prevent you from holding on to water, so your skin looks sort of prune-like (i.e., wrinkles). 

   • So if you're drinking a lot of caffeine or alcohol, remember to stay hydrated.

Finally, we conclude this article with what Dr. Weil has said[5]:

"Sensitivity to caffeine varies greatly from person to person. Some people who drink one cup of coffee a day are physically addicted to it, will experience a withdrawal reaction if they cut it out, and have any number of physical and emotional symptoms caused by it. Others can drink many cups a day without any of that."

1. Change Your Brain Change Your Body by Daniel G. Amen, M.D.

2. Ultra-Longevity by Mark Liponis, MD

3. How to Manage Your Migraines by Chrystle Fiedler. The Costco Connection, November 2010

4. Your Brain on Food by Gary L. Wenk

5. Spontaneous Happiness by Andrew Weil, MD

6. Coffee Linked to Vision Loss

7. Got a Hankering for Fast Food? Skip the Coffee, Study Says

8. Caffeine: How much is too much?

9. Caffeine May Enhance Memory

10. Caffeine content for coffee, tea, soda and more

11. Half Life of Caffeine

12. Dark Chocolate: The Boost Your Brain Needs

    • As theobromine, the cousin of caffeine, is a myocardial stimulant as well as a vasodilator, it increases heartbeat, and also dilates blood vessels, causing a reduced blood pressure.

13. Caffeine: The Silent Killer of Emotional Intelligence

    • New research from Johns Hopkins Medical School shows that performance increases due to caffeine intake are the result of caffeine drinkers experiencing a short-term reversal of caffeine withdrawal. 

    • In reality, the caffeine is just taking your performance back to normal for a short period.

14. What caffeine does to your body and brain

    • Caffeine can raise acid levels in your stomach, whcih can lead to heartburn and can be especially bad if you suffer from ulcers.

15. The ancient fat-burning tea you need to start drinking

    • Pu-erh is different than most teas, as it undergoes a natural fermentation process and is aged like a fine wine.

16. Caffeine: How much is too much?

17. Your daily cup of coffee may be aging your skin

18. Should You Drink Coffee or Wear It? (slide 10) 

19. Caffeine Overdose Killed South Carolina Teen, Coroner Rules