What are the effects of caffeine?

From the Guidelines

Caffeine consumption of up to 400mg per day, roughly 3-4 cups of coffee, is generally safe for healthy adults and may have benefits such as reducing the risk of cardiovascular disease, type 2 diabetes, and Parkinson's disease. The effects of caffeine are mostly related to the stimulation of the central and sympathetic nervous system, providing a feeling of alertness after consumption 1. Caffeine typically takes effect within 30-60 minutes after consumption and has a half-life of about 5-6 hours in most adults. While moderate caffeine consumption is generally safe for most people, excessive intake can cause side effects including insomnia, jitteriness, increased heart rate, headaches, and anxiety.

Key Considerations

• Pregnant women should limit intake to 200mg daily, as advised by the European Food Safety Authority 1.
• Those with certain medical conditions like heart problems, high blood pressure, or anxiety disorders should consult healthcare providers about appropriate consumption levels.
• Caffeine can interact with certain medications, so it's essential to check with your doctor if you're taking prescription drugs.
• Abruptly stopping caffeine consumption after regular use can lead to withdrawal symptoms like headaches and irritability, so gradual reduction is recommended if you wish to decrease your intake.

Special Populations

• Children and adolescents metabolize caffeine more rapidly than adults, and high caffeine intakes may be associated with an increased risk of anxiety and withdrawal symptoms in this population 1.
• The recommended intake for children and adolescents is less than 2.5 mg/kg body weight per day, which is equivalent to about 1 or 2 cups of tea or 1 small cup of coffee daily 1.

Overall Recommendation

Moderate caffeine consumption, defined as up to 400mg per day, can be a part of a healthy diet for most adults, but individual tolerance and sensitivity to caffeine can vary greatly. It's crucial to be aware of the potential risks and benefits of caffeine consumption and to consult with a healthcare provider if you have any concerns.

From the FDA Drug Label

ADVERSE REACTIONS Overall, the reported number of adverse events in the double-blind period of the controlled trial was similar for the caffeine citrate and placebo groups. Adverse events described in the published literature include: central nervous system stimulation (i.e., irritability, restlessness, jitteriness), cardiovascular effects (i.e., tachycardia, increased left ventricular output, and increased stroke volume), gastrointestinal effects (i.e., increased gastric aspirate, gastrointesti­nal intolerance), alterations in serum glucose (hypoglycemia and hyper­glycemia) and renal effects (increased urine flow rate, increased creatinine clearance, and increased sodium and calcium excretion).

The effects of caffeine include:

• Central nervous system stimulation: irritability, restlessness, jitteriness
• Cardiovascular effects: tachycardia, increased left ventricular output, and increased stroke volume
• Gastrointestinal effects: increased gastric aspirate, gastrointestinal intolerance
• Alterations in serum glucose: hypoglycemia and hyperglycemia
• Renal effects: increased urine flow rate, increased creatinine clearance, and increased sodium and calcium excretion 2

From the Research

Effects of Caffeine on Human Health

• Caffeine is a widely consumed dietary ingredient that can have both positive and negative effects on human health 3, 4, 5, 6, 7
• Moderate caffeine consumption is considered safe and has been linked to several health benefits, including:
  • Physical endurance and reduction of fatigue 3
  • Enhancing mental alertness and concentration 3
  • Weight loss and reduction of the overall risks for developing the metabolic syndrome 3
  • Protective effects on cardiovascular diseases, obesity, diabetes mellitus, cancers, and neurodegenerative and liver diseases 7
• However, excessive caffeine intake can lead to negative effects, including:
  • Caffeine intoxication, which can cause symptoms such as restlessness, rapid heart rate, muscle tremors, nausea, vomiting, and confusion 4, 5
  • Increased risk of fatal overdose, particularly in children and pregnant women 4, 5, 6
  • Side effects such as addiction, insomnia, migraine, and other adverse effects 7
• The recommended daily intake of caffeine varies depending on the individual, with:
  • Healthy adults: up to 400 mg per day (equivalent to 6 mg/kg body weight per day) 6
  • Reproductive-aged women: no more than 300 mg per day (equivalent to 4.6 mg/kg body weight per day) 6
  • Children: no more than 2.5 mg/kg body weight per day 6
  • Pregnant women, children, and adolescents: restricted or reduced intake to avoid potential adverse effects 7