Have you ever experienced a situation where you’re extremely tired, but your mind remains unusually alert? Upon reflection, the main suspect for your sleeplessness might be the coffee or tea you had earlier. So, how long before bed should you drink coffee to avoid impacting your sleep? How significant is the effect of caffeine on the body, and what does caffeine addiction mean for your health? What should you keep in mind when consuming caffeine? Let’s delve into these questions today.

Drink 250 ml of Coffee at Least 8-9 Hours Before Bed

To give a straightforward answer:

  • About 100-110 mg of caffeine: more than 8.8 hours before bedtime.
  • About 200-220 mg of caffeine: more than 13.2 hours before bedtime.

This means if you plan to go to bed at 10 PM:

  • If you want to drink a standard 250 ml cup of coffee (or any drink with the equivalent amount of caffeine), it’s best to consume it before 1:12 PM.
  • If you plan to drink a 500 ml cup of standard coffee (or any drink with the equivalent amount of caffeine), you should have it before 8:50 AM.

These conclusions come from a systematic review and meta-analysis published this year in the journal Sleep Medicine Reviews. The analysis included 24 studies on caffeine intake and sleep, conducted up until June 2021.

Research Shows Caffeine Intake Before Bed Reduces Total Sleep Time and Efficiency

Apart from determining the safest time to drink coffee or other caffeinated beverages before sleep, the study also found that caffeine intake can shorten total sleep time by 45 minutes and reduce sleep efficiency by 7%. It extends light sleep duration (+6.1 minutes) and reduces deep sleep duration (-11.4 minutes).

The closer the high-dose caffeine intake is to bedtime, the shorter the total sleep time (though the exact dose-response relationship is still unclear).

However, if the caffeine dose isn’t high, even close to bedtime, it may not significantly disturb total sleep duration. For example, a cup of tea containing about 50 mg of caffeine per 250 ml is relatively sleep-friendly. The key takeaway is that toxicity cannot be discussed without considering the dose.

Interestingly, if you drink a high-caffeine beverage (like several hundred milliliters of coffee or milk tea) 30 minutes before bed, it might not delay your sleep onset. This is because caffeine typically takes 30-120 minutes to be absorbed through the digestive tract and reach peak concentration in the blood (with individual differences). Therefore, drinking it immediately before bed may not affect the time it takes to fall asleep. However, it will definitely impact your total sleep duration, the duration of deep sleep, and overall sleep efficiency – both the quality and quantity of your sleep will be compromised.

The study’s limitations suggest that these conclusions may be more applicable to individuals who don’t consume large amounts of caffeine regularly. For those who drink several cups of coffee or milk tea daily and have developed a tolerance, bedtime proximity may not significantly affect sleep onset.

Many Hidden Sources of Caffeine in Daily Diet

Even if you’re tolerant to caffeine and it doesn’t significantly affect your sleepiness, it’s still advisable to consume coffee and milk tea in moderation and avoid addiction.

Besides coffee and milk tea, other foods like energy drinks, chocolate, and cola also provide caffeine. Healthy adults should limit their daily caffeine intake to 400 mg. For pregnant or breastfeeding women, it’s best to limit it to 200 mg per day.

Excessive caffeine consumption can lead to negative effects, such as increased irritability and anxiety, or impact body weight due to added ingredients like milk, creamers, and sugar.

Why Does Caffeine Make You Alert? It Competes with Adenosine

Caffeine’s ability to make you alert is why many people are drawn to coffee, energy drinks, chocolate, and tea, in addition to their inherent appeal.

Caffeine’s structure is similar to adenosine, allowing it to competitively bind to adenosine receptors, blocking adenosine’s effects. Simply put, caffeine takes adenosine’s place.

Adenosine promotes sleepiness when it binds to its receptors. When caffeine binds instead, it prevents this sleep-promoting effect, making you feel more awake.

After Providing a Temporary Boost, What Are Caffeine’s Effects on the Body?

However, caffeine’s competitive binding is a double-edged sword.

  1. Caffeine cannot compensate for the decline in performance due to chronic sleep deprivation. It only provides a temporary boost.
  2. Late caffeine intake, such as a post-work drink for evening activities, will affect sleep quality and may cause anxiety.
  3. Habitual caffeine consumption can lead to addiction. Abrupt cessation can result in withdrawal symptoms like headaches, fatigue, reduced alertness, and mood changes, resembling flu symptoms. These symptoms are most severe 1-2 days after stopping caffeine and can last up to 2-9 days. Reducing caffeine intake gradually rather than abruptly can help alleviate these symptoms.

This is why the alertness effect is more pronounced in those who do not regularly consume caffeine or who have recently stopped and then resumed.

Relying on Coffee or Energy Drinks? Keep Two Things in Mind

For those relying on coffee or energy drinks, consider these points:

  1. Tolerance Reduction – You may need more caffeine over time for the same effect, increasing potential health impacts.
  2. Avoid Excessive Energy Drink Consumption – Especially high-concentration small bottles, and never mix with alcohol, as this can lead to severe cardiovascular, psychological, and neurological effects, potentially fatal. Parents should monitor children’s and teenagers’ consumption of these drinks.

Confirm Three Things Before Drinking Energy Drinks

Many people don’t realize that energy drinks often have high caffeine content. Typically, 1000 ml contains about 320 mg of caffeine. Large intake (e.g., 1000 ml in half a day) can cause cardiovascular issues like elevated blood pressure, prolonged QT interval, and palpitations. Energy drinks often accompany alcohol or intense exercise, exacerbating these effects. To avoid accidents, follow these guidelines:

  1. Confirm that caffeine content does not exceed 200 mg per drink.
  2. Avoid consuming more than 200 mg of caffeine at a time.
  3. Do not drink energy drinks and alcohol together.

Conclusion

Moderate your caffeine intake, be aware of hidden sources, and avoid reliance on high-caffeine beverages to maintain good sleep quality and overall health.