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How Caffeine Impacts the Body

It might be a morning ritual, an after-lunch pick-me-up, or a nightcap, but drinking coffee is a part of the day for more than 60% of Americans. About half of people in the United States also have at least one soda per day. Add in all the tea, chocolate and energy drinks and that’s a lot of caffeine consumed. So how does all this caffeine impact a person’s body?

Caffeine is a stimulant that affects the body’s central nervous system. It’s found naturally in some foods like coffee, tea and certain chocolates. It’s also added to other beverages and foods to sell as an energy boost. For many, caffeine helps with waking up in the morning and allows for better concentration throughout the day. But for those sensitive to caffeine, it may lead to headaches, a rapid heart rate or trouble sleeping.

Caffeine levels in common drinks

About 400 milligrams (mg) each day is believed to be a safe level for most adults, according to the U.S. Food and Drug Administration. This equals about four cups of coffee, 10 cans of cola or two energy shot drinks.

Here are the caffeine levels in common drinks:

  • 8 oz. brewed coffee: 96 mg
  • 8 oz. black tea: 47 mg
  • 8 oz. cola (soda): 22 mg

Pregnant and breastfeeding women should talk with their doctor and limit their caffeine intake to 200 mg daily, or about two cups of coffee. The American Academy of Pediatrics discourages children from drinking caffeine beverages, but adolescents 12 and older should limit consumption to 100 mg per day (two to three cans of cola or one cup of coffee).

Because studies looking at the link between high caffeine consumption and heart disease are conflicting, those with high blood pressure or who have had a heart attack should discuss caffeine consumption with their physician.

Processing caffeine

For many, a cup of coffee is part of what nudges them to get out of bed each morning. Many people report feeling the effects of caffeine within about 15 minutes. In the bloodstream, caffeine levels peak about an hour after that first drink. It can stay at this level for several hours. 

Digesting caffeine

The stimulant activity of caffeine is not limited to our brain, but our colon too. Caffeine stimulates muscle contractions in the colon. These contractions promote peristalsis, or the contraction and relaxation of muscles, which can help promote a bowel movement.

On the flip side, caffeine doesn’t cause everyone to have a bowel movement. Caffeine is a diuretic, which can increase urination and thereby cause constipation.

Caffeine takes a long time to digest. Up to six hours after drinking a caffeinated beverage, about half of the caffeine remains in the system. Experts say it can take up to 10 hours for caffeine to completely leave a person’s bloodstream. Just like caffeine helps some people wake up in the morning, it can also make it more difficult to sleep at night. To avoid sleep disruption, some may need to avoid caffeinating about six hours before bedtime. 

Coffee consumption can pose issues for some individuals with gastrointestinal conditions including:

  • Crohn’s disease
  • Ulcerative colitis
  • Irritable bowel syndrome

For individuals with these conditions, it’s best to avoid caffeine during a flare-up. Because of the acidic nature of coffee, it can also disrupt the intestinal lining and exacerbate symptoms for those with gastritis or reflux.

What to drink before coffee in the morning

While many reach for that first cup of coffee before anything else, it might be better to do a couple of other things first. Because many wake up feeling a little dehydrated after not drinking anything for six to eight hours, try these before anything caffeinated:

  • A glass or two of water (lukewarm might be best)
  • A cup of herbal tea
  • Water with a lemon slice
  • A breakfast food item

Caffeine affects all individuals differently. While some may experience the effects of caffeine for a couple of hours, others may need to curb their caffeine consumption in the afternoon to get a quality night of sleep.

Shanthi Appelö is a registered dietitian and health and wellness spokesperson at Blue Cross Blue Shield of Michigan. For more health tips and information, visit

A Healthier Michigan
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