9 Surprising Ways Caffeine Impacts Brain Health

For many people, the morning starts with coffee, soda, tea, or an energy drink. It’s an attempt to boost energy, mood, and alertness — to sharpen your mind for the day. You may feel like that caffeine buzz is boosting your brainpower. But there’s a downside. 

Caffeine is not an innocuous substance. In fact, recent studies have suggested that regular caffeine intake may have negative impacts on brain health, from the brain’s actual size to how it functions. The regular intake of caffeine can also trigger withdrawal symptoms — you may have experienced a headache when you go without your morning joe — and mood swings.

Here are nine surprising side effects that regular caffeine consumption can cause in terms of brain health: 

1. Caffeine shrinks the brain. As a brain health expert who has built the world’s largest database of brain scans related to behavior, I can assure you that when it comes to the brain, size matters! A 2022 study published in Nutritional Neuroscience found that individuals who drink more than six cups of coffee per day may be at a higher risk of decreased brain volume, dementia, and stroke.
2. Caffeine changes brain structure. Regular intake of caffeinated beverages causes significant changes in the gray matter in the brain, according to a 2021 study. A decrease in gray matter was most pronounced in an area of the brain that includes the hippocampus, which is heavily involved in memory consolidation. The significant changes don’t appear to be permanent, however, as brain volume returned following ten days of abstinence from caffeine.
3. Caffeine reduces cerebral blood flow. One study found that a 250-milligram dose of caffeine (the equivalent of drinking two or three cups of coffee) reduces blood flow in the brain by 22-30 percent. Anything that decreases blood flow reduces brain function. Our brain-imaging work at Amen Clinics shows that low blood flow is associated with depression, ADHD, substance abuse, and traumatic brain injury. 
4. Caffeine dehydrates the brain. When consumed in large amounts — more than five cups of coffee, for example — caffeine can be dehydrating. This can impact the human brain, which is roughly 80 percent water. If your brain becomes even mildly dehydrated, it can cause problems. According to a 2018 meta-analysis, being just 2 percent dehydrated can lead to impaired cognitive performance in tasks involving executive function, attention, and motor coordination. Other issues related to dehydration include anxiousness, depression, confusion, trouble focusing, and memory problems. If you drink caffeinated beverages, it’s important to drink adequate amounts of water to make up for it.  
5. Caffeine interferes with connectivity in the brain. A fascinating study published in 2021 suggests that consuming high doses of caffeinated beverages like coffee reduces functional connectivity in certain areas of the brain. In particular, guzzling caffeine affects the limbic system (emotional centers) and somatosensory network (involved in touch and tactile perception). The bottom line? More stress and anxiety.  
6. Caffeine activates the brain’s reward system. Researchers have known for decades that caffeine increases production of dopamine within the pleasure circuits of the brain. The uptick in the feel-good neurotransmitter acts as a mood-booster. If you decide to quit your caffeine habit, going cold turkey can lead to symptoms of withdrawal, including grumpiness, headaches, and tiredness. These symptoms usually begin about one to two days after your last cup of coffee, energy drink, soda, or tea and can last a few days or up to a week.
7. Caffeine increases inflammation in some people. Although coffee is touted as having anti-inflammatory properties, it can have the opposite effect in some individuals. It all depends on your genetics and how your body metabolizes caffeine. In those who are fast caffeine metabolizers, it isn’t an issue. In slow caffeine metabolizers, however, the substance can spark an inflammatory reaction and increase cortisol levels, according to findings in JAMA.
8. Caffeine causes highs and lows. That awesome energy and mood boost you get from downing a cup of coffee, energy drink, or soda doesn’t last. Caffeine’s effects on the brain can last anywhere from 1.5 to 9.5 hours, but they typically last only about five hours. After the caffeine effect is gone, you can expect a post-caffeine slump. 
9. Caffeine interferes with sleep. Research shows that caffeine blocks a brain molecule called adenosine, which is heavily involved in our sleep-wake cycle. Caffeine consumption can trick the brain into a sense of wakefulness when you should be feeling sleepy. As a result, a chronic lack of sleep can lead to a host of other negative changes in the brain. 

Many people love the temporary boost they get from caffeine. But as a brain health expert, I usually recommend that people cut down on caffeine consumption, if not eliminate it completely. Whether it’s issues with memory, sleep, mood swings, inflammation, increasing your risk for stroke, or other factors, the short-term jolt isn’t worth the long-term consequences. Try cutting back or doing without — and see if you can boost your brain energy in other less harmful ways.

Written by Dr. Daniel G. Amen, MD.
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