Test Your Knowledge

Although most studies have shown no correlation between caffeine consumption and medical problems, people are encouraged to ask their physician about the potential health risks posed by caffeine use. The answer to that question may differ depending on a patient’s circumstances.

For example, a physician may advise against caffeine use in women who are pregnant or breastfeeding. Although no studies have shown a conclusive link between caffeine consumption and damage to a fetus or nursing child, experts usually err on the side of caution in these cases. In addition, some studies have indicated that consuming high levels of caffeine while breastfeeding may be associated with lower sleep levels and poor feeding in the baby.

A physician may also recommend limited use of caffeine for those who have certain types of illnesses, such as coronary artery disease, peptic ulcers, primary insomnia, generalized anxiety disorder, gastroesophageal reflux, urinary incontinence, gastritis or high blood pressure.

Physicians can inform patients about possible interactions between caffeine and other medications or supplements a patient may be taking, including:

• Antibiotics. These drugs may interfere with the breakdown of caffeine in the body, increasing the amount of time that caffeine acts on the body.
  
  
• Ephedra. This dietary supplement is known to cause serious health problems such as heart attacks, strokes or seizures. Combining ephedra with caffeine may increase the risk of such problems.
  
  
• Theophylline. Combining use of this bronchodilator (used to treat asthma) with caffeine can increase the concentration of the drug in the bloodstream, leading to symptoms such as nausea, vomiting and heart palpitations.  

Children also should limit their intake of beverages that contain caffeine, including sodas and sports drinks. High levels of caffeine affect children in ways that are similar to the effects on adults. The United States does not have maximum intake guidelines for caffeine in preschool children, but Canada recommends that preschool children avoid consuming more than 45 milligrams (mg) of caffeine per day. Experts report that caffeine will not stunt a child’s growth.

Caffeine’s impact varies from person to person. Some people are not greatly affected, while others may be especially susceptible to the effects of caffeine use. Several factors may be involved in increased sensitivity to caffeine. They include:

• Body mass. People with smaller body mass feel the effects of caffeine more quickly.
  
  
• History of caffeine use. People who do not regularly use caffeine may be more susceptible to its effects. Regular use of caffeine helps an individual to build up a tolerance to the substance.
  
  
• Stress. All forms of stress increase a person’s susceptibility to caffeine.

Other factors that may contribute to caffeine sensitivity include age, smoking habits, medication or hormone use, and health conditions such as anxiety disorders. In addition, if a beverage contains certain additional ingredients (e.g., guarana, ginseng), the stimulating effect of caffeine is increased. Although age may play some role in a person’s sensitivity to caffeine, most studies have shown that caffeine affects children and adults in a similar manner.

Research has also shown that as little as 100 mg of caffeine per day can cause some people to become tolerant to caffeine. This can also result in withdrawal symptoms such as headaches, drowsiness and difficulty concentrating when the usual amount of caffeine is not consumed. These withdrawal symptoms usually disappear within a day or two after restricting or eliminating caffeine use.

Experts generally agree that for most people, caffeine does not pose serious health risks when moderate amounts are consumed, such as between 250 and 350 mg per day. Even when a person experiences effects of caffeine consumption, such as increased heart rate, anxiety, the jitters or insomnia, these effects only last for a few hours since caffeine does not accumulate in the body.

People who do not use caffeine regularly are likely to experience positive mood effects when they consume low amounts of the substance. They may feel happy, alert, energetic and more sociable. People who regularly consume caffeine also feel a boost when the substance enters their body, but this is more likely to be a response to the caffeine’s effect of suppressing withdrawal symptoms.

People who consume large amounts of caffeine at once often experience temporary negative effects, such as anxiety, nervousness and an upset stomach. Some studies also indicate that high levels of caffeine may cause an increase in anxiety levels and panic attacks. 

For years, researchers have looked for potential links between caffeine use and health conditions such as cancer, fibrocystic breast disease, cardiovascular disease, cholesterol levels, ulcers, inflammatory bowel disease, infertility, birth defects and osteoporosis. To date, no scientific evidence has emerged that links caffeine use to any of these disorders, according to the American Dietetic Association. 

The U.S. Food and Drug Administration has classified caffeine as generally recognized as safe (GRAS) since 1958, and the American Medical Association also has stated its belief that caffeine is safe when used in moderation.

Drinking two to three cups of coffee has been shown to raise blood pressure in people who do not have high blood pressure. The reason for this remains unclear. However, there is no evidence that this rise in blood pressure is permanent or that it causes significant health risks. The rise in blood pressure associated with caffeine use lasts only a few hours and is equivalent to the rise experienced after climbing a flight of stairs. 

The long-term effect of caffeine on blood pressure remains unclear, although many experts do not believe that the substance poses significant health risks related to blood pressure.

Drinking coffee or other caffeinated beverages also has a diuretic effect, meaning that it causes water loss through increased urination. However, the water that is lost is usually balanced by the amount of fluid obtained from the beverage.

Consuming caffeine slightly increases the loss of calcium through urine and feces. The amount of calcium lost with each cup of coffee is equal to the amount of calcium contained in 1 teaspoon of milk. Thus, adding milk to coffee easily restores the calcium lost through caffeine use. People who consume caffeine in moderation do not raise their risk of osteoporosis.

Although caffeine is safe when moderately used, increased levels of caffeine may have certain health consequences. People who drink more than 500 to 600 mg of caffeine a day (approximately four to seven cups of coffee) may experience the following symptoms:

• Abnormal heart rhythms
• Anxiety
• Headaches
• Irritability
• Muscle tremors
• Nausea, diarrhea or other gastrointestinal problems
• Restlessness
• Sleeplessness

Extraordinarily high caffeine intake (150 mg per kilogram of body weight) can lead to serious health consequences. Even moderate caffeine intake can create symptoms of caffeine overdose in certain people who are highly sensitive to caffeine.

People who drink high levels of caffeine often have trouble sleeping at night. They wake in the morning feeling fatigued and drink coffee or another caffeinated beverage throughout the day to help them stay awake. This in turn causes them to again have trouble falling asleep, creating a cycle that leaves a person increasingly tired as the cumulative effects of sleeplessness build up. 

Symptoms of caffeine overdose include:

• Flushed face
• Frequent need to urinate (diuresis)
• Rapid heart rate (tachycardia)
• Restlessness or feeling jittery
• Shakiness
• Throwing up (vomiting)
• Trouble sleeping (insomnia)
• Upset stomach (nausea)