Let's take a closer look at a variety of studies of the effects of caffeine, starting with a handful of animal studies.
In a study reported in the journal Biochemical and Biophysical Research Communications 2007 rats were given a long term low dose of caffeine representative of normal human intake and it was found that the normal formation of nerve cells, what is called neurogenesis, was inhibited in the part of the brain called the hippocampus. which is associated with learning and memory. with the result that their learning and memory ability was impaired. In the normal human brain and rat brain new nerve cells are produced throughout life. However the number of new cells was significantly decreased in the caffeine fed rats. The concern here is that the same thing could occur in the human hippocampus that is exposed to caffeine.
A study reported in the journal PLoS ONE 2008 describes giving caffeine to pregnant mice that produced blood levels the same as in humans after drinking 3-4 cups of coffee. They found long lasting behavioral changes that carried down to offspring in the second generation of mice. The authors stated it was not possible to decide whether these changes were good.
Now for the last animal study. This one was reported in 2009 in the FASEB Journal. A single dose of caffeine was given to pregnant mice that gave blood levels equal to 2 cups of coffee in humans.
The half-life (the time it takes for half the amount of a drug or chemical in an animal or human to be broken down or metabolized normally) of coffee in mammals such as humans and mice ranges from 3 to 6 hours. In pregnancy this increases to 10-20 hours. In the fetus the half life can be as long as 80-100 hours since the fetus is unable to metabolize the caffeine. Because of this the exposure to caffeine, which may seem modest in the mother, may be much more significant in the fetus. Now note this-from one single dose of caffeine there were long-term changes in the way the mice baby's heart functioned.
Now we want to consider how caffeine affects humans. We have already alluded to how it affects folks with alcohol and nicotine addiction and how it may lead to those addictions. As we consider these points, you will find citations to the journals referenced, should you wish to read up on your own.
Dr. Roland Griffiths, who was mentoned previously, states caffeine is an addictive substance and some people suffer withdrawal symptoms when they stop using caffeine.
Numerous authors have mentioned that caffeine is the most widely used psychoactive substance in the world. There are many references in psychiatric journals to adverse reactions to caffeine in people with mental problems. Also that caffeine can alter the way psychiatric medicines work. Caffeine can bring on a "panic attack" in people who have what is known as panic disorder. Comprehensive Psychiatry 2007.
In the 2008 BMJ ( British Medical Journal) it was reported that the daily drinking of 200 mg (milligrams) of caffeine-the amount in 11/2 to 2 cups of coffee-would cut down the blood flow to the placenta in pregnant woman by 25 percent.
It would also cut down on the growth of the fetus. In fact , even the lowest level of caffeine consumption appeared to cause smaller babies to be born. This fact has led some doctors to warn pregnant women not to use caffeine. And there are some who say that any woman who is planning on getting pregnant should abstain from caffeine in any form.
Osteoporosis or thinning of the bones -- Women who drank more than 300 mg per day (about 3 cups of coffee had greater thinning of the bones, especially if there was a genetic abnormality in the way the body handled Vitamin D. Journal of Steroid Biochemistry and Molecular Biology 2007.
Poor iron absorption -- A cup of coffee reduced the absorption of iron from a hamburger meal by 39 percent. This could be a problem if a person was already anemic. American Journal of Clinical Nutrition 1983
Reduced blood flow to the brain -- There were four articles showing that this happens. This would not be good news for a person who had already had a stroke.
An increase in impulsivity or sensation seeking-associated with more than 200 mg of caffeine per day. Progress in Neuropsychopharmacology and Biological Psychiatry 2007.
Insomnia -- Due to the differences in the way people metabolize caffeine some folks who are regular user of caffeinated drinks have sleep problems. Clinical Pharmacology and Therapeutics 2009.
Over weight -- A Cleveland, Ohio, study showed that overweight adolescents were more likely to be male, to have higher caffeine intake and less sleep times. This report was made in 2007.
Dependence on caffeine as teenagers -- Thirty-six adolescents who daily consumed caffeine were interviewed, and 77.8 percent described withdrawal symptoms after stopping or reducing their intake. The authors stated that these findings are important due the vast numbers of adolescents who drank caffeinated beverages. Drug and Alcohol Dependence 2002.
Cardiovascular and neuroendocrine activations at home and at work. Putting this in more simple language it is talking about how caffeine affected the heart and blood vessels and the nervous system and the hormones connected with the nervous system. Healthy folks who were regular coffee drinkers were given 250 mg of caffeine (about what would be in 21/2 cups of coffee) in the morning and 4 hours later and were checked several times until bedtime. All of them showed significant elevations of blood pressure. Furthermore the excretion of adrenaline in the urine was increased by 32 percent. What the long term results of this is a bit uncertain but it does show that even in regular coffee drinker there were measurable changes in important body systems. Psychosomatic Medicine 2002.
The effect of black tea and coffee and the risk of lung cancer among current and former smokers -- In a study done a the Roswell Park Cancer Cancer Institute ( which is a respected cancer institute) in Buffalo, N.Y., people who drank 2-3 cups of coffee daily had an increased risk of getting lung cancer. It was the feeling at the Institute that the phytochemicals including the antioxidants were overshadowed by the elevated risk associated with caffeine.
Next week, we'll look into claims that caffeine helps to prevent type II diabetes.
Dr. Don Casebolt of College Place is a retired physician who is passionate about preventive medicine. He spent 4 years as a medical officer in the U.S. Navy, the last 21/2 years as a flight surgeon. He also worked on the Navajo Reservation for 22 years.