As a stimulant of the central nervous system, caffeine is a widely consumed substance by many individuals the World over. It is esitmated that somewhere between 80-90% of Adults in the UK consume some form of caffeine daily. Beyond its well-known ability to increase alertness, caffeine has various effects on the human body. This article aims to provide a comprehensive overview of these effects.
According to the European Food Safety Authority (EFSA)*, a safe daily intake level of caffeine for adults is 400 milligrams per day, which is roughly equivalent to about four cups of coffee. This amount of caffeine is considered safe for most healthy adults and is unlikely to cause adverse effects. However, it is important to note that individual tolerance and sensitivity to caffeine can vary greatly, and some people may experience negative side effects at lower levels of consumption. It is also important to keep in mind that caffeine is not just found in coffee, but also in tea, energy drinks, chocolate, and some medications, so it is important to monitor total daily intake from all sources.
Central Nervous System
As a central nervous system stimulant, caffeine increases alertness, reduces fatigue, and is commonly found in medications to manage drowsiness, headaches, and migraines. Regular coffee consumption has been linked to a reduced risk of Alzheimer's and dementia, and a 45% reduction in suicide risk. However, these benefits are only present in coffee containing high levels of caffeine and not in decaf coffee.
Withdrawal symptoms may occur if caffeine consumption is suddenly stopped. These symptoms can include headaches, anxiety, irritability, drowsiness, and in rare cases, tremors. It's also possible to overdose on caffeine, which can lead to confusion, hallucinations, vomiting, convulsions, and even death (in extreme cases).
The safe limit of caffeine intake is 400 milligrams, equivalent to 4 cups of coffee*.
Digestive and Excretory Systems
Caffeine increases the acidity in the stomach and may cause- heartburn or stomach discomfort. It's processed in the liver and eliminated through urination, leading to increased urination shortly after consuming caffeine. Individuals with acid reflux or ulcers should consult a doctor before consuming caffeine.
Circulatory and Respiratory Systems
Absorbed in the stomach, caffeine reaches its highest levels in the bloodstream within one to two hours. It can temporarily increase blood pressure, either by increasing adrenaline or blocking hormones that widen the arteries. In most individuals, there is no long-term effect on blood pressure. However, individuals with irregular heart rhythms or high blood pressure should consult a doctor before consuming caffeine. An overdose of caffeine can lead to rapid or irregular heartbeat and breathing difficulty, and in rare cases, death from convulsions or irregular heartbeat.
Skeletal and Muscular Systems
Excessive caffeine consumption can interfere with calcium absorption and metabolism, contributing to bone thinning (osteoporosis). Additionally, excessive caffeine can cause muscle twitching. Withdrawal symptoms may include achy muscles.
Reproductive System
Caffeine is transported in the bloodstream and crosses the placenta. As a stimulant, it can increase the heart rate and metabolism of a developing fetus and may lead to slowed fetal growth and an increased risk of miscarriage. While limited caffeine intake is generally safe during pregnancy, it is generally recommended to limit consumption to 200-300 milligrams per day for individuals trying to conceive, as large amounts of caffeine may interfere with estrogen production and metabolism necessary for conception.
How long does Caffeine Stay in your System?
The effects of caffeine are noticeable within 30 to 60 minutes of consumption and can last up to 5 hours, as caffeine has a half-life of up to 5 hours. The half-life refers to the time taken for the amount of a substance to reduce to half its original quantity. People with caffeine sensitivity may experience symptoms for several hours or even a few days. The American Academy of Sleep Medicine recommends avoiding caffeine at least six hours before bedtime.
Caffeine is naturally found in plants such as coffee beans, tea leaves, and cocoa beans and can also be added to sodas and energy drinks. Withdrawal symptoms from caffeine may include headaches, depression, anxiety,
drowsiness, and fatigue, and can occur within 12 to 24 hours after the last caffeinated item. The best way to reduce caffeine intake is to gradually decrease consumption.
The amount of caffeine in coffee or tea varies based on factors such as brewing method, type of beans or leaves, and processing techniques. A small, regular coffee cup contains 95-165 mg of caffeine, while a cup of decaf coffee has 2-5 mg.
For a healthy lifestyle, the daily caffeine intake should be limited to 300 mg, equivalent to 3 small, regular coffee cups. Other ways to increase energy include drinking water, getting 7-9 hours of sleep, avoiding naps, eating plant-based foods, exercising, and speaking to a doctor if feeling tired regularly. Energy levels can also be affected by underlying conditions such as depression.
*Source: European Food Safety Authority (EFSA). (2015). Scientific Opinion on the safety of caffeine. EFSA Journal, 13(5), 4102. https://efsa.onlinelibrary.wiley.com/doi/pdf/10.2903/j.efsa.2015.4102