Caffeine, your favorite drug

For many people around the world, waking up is synonymous with having a cup of coffee. According to a 2015 Gallup poll, 64% of Americans report drinking at least 1 cup of coffee a day and the average person drinks 2.7 cups of coffee a day.

How coffee is made:

Coffee beans that we know and love are actually not beans at all- they are seeds! According to the National Coffee Association of USA, once processed, the seeds can be used to brew coffee. If they are not processed, the seeds can be planted and grow into new coffee trees. The seeds themselves come from the fruit of coffee trees, known as coffee cherries. After the cherries have been picked, they are processed through either a dry or wet method in order to remove the pulp. These “beans” are they dried, milled, and exported before they are tasted for quality. They are they roasted, ground, and finally sent on their way to be brewed.

How caffeine works:

According to the concept of sleep homeostasis, sleep is a compensatory response to the preceding waking episode. The longer you have been awake, the greater the pressure to sleep. This pressure to sleep is mediated by adenosine, which increases in concentration the longer you are awake. Adenosine depresses central nervous system activity and causes you to be more sleepy. Caffeine has a similar structure to adenosine, and ends up binding to all of the adenosine receptors. This means that the adenosine molecules can no longer be sensed by the cells which is why you are prevented from feeling sleepy.

Different sources of caffeine:

According to the FDA, healthy adults should limit their caffeine intake to a maximum of 400 mg, which is the equivalent of about 4 to 5 cups of coffee. Exceeding this amount may result in anxiety and irritability. Coffee may be a common beverage, but it is not the only drink or food item that contains caffeine. Take a look at the following chart to see how your your caffeine consumption measures up to the recommended maximum:


Product Serving Size Caffeine (mg)
Coffee, brewed 1 cup (8 oz) 95
Espresso 1 oz 64
Coffee, instant 8 oz 62
Coffee, brewed, decaf 1 cup (8 oz) 2
Lipton Black Tea 1 cup 55
Lipton Original Iced Tea 16 oz 50
Tea, brewed 1 cup (8 oz) 47
Lipton 100% Green Tea 1 cup 45
Tea, instant, unsweetened 1 cup (8 oz) 26
Lipton Brisk Tea 12 oz 9
Tea, herbal 1 cup (8 oz) 0
Energy Drinks
Monster 16 oz 173
NOS 16 oz 160
Rockstar 16 oz 158
Full Throttle 16 oz 158
Amp 16 oz 149
Red Bull 12 oz
(16 oz equivalence)
Red Bull 8.4 oz
(2 can equivalence)
Pepsi One 12 oz 54
Mountain Dew 12 oz 53
Mello Yellow 12 oz 52.5
Diet Coke 12 oz 46.5
Pepsi 12 oz 37.5
Diet Pepsi 12 oz 36
Coca Cola Classic 12 oz 34.5
Caffeine free Coke, Pepsi 12 oz 0.0
Sprite, 7-Up 12 oz 0.0
NoDoz 1 tablet 200
Vivarin 1 tablet 200
Extra Strength Excedrin 2 tablets 130
Anacin 2 tablets 64
Chocolate chips, semi-sweet 1 cup (6 oz bag) 104
Chocolate chips, milk chocolate 1 cup 34
Baking chocolate, unsweetened 1 square 23
Milk chocolate bar 1 bar (1.55 oz) 9
Chocolate pudding, ready-to-eat Snack size (4 oz) 6
Frozen yogurt, chocolate 1 cup 5
Chocolate ice cream 1 cup 4
Hot cocoa 1 packet, 6 oz water 4
Chocolate syrup, fudge-type 2 tbsp 3
Chocolate-chip cookie, packaged 1 cookie 1

Sources: Data compiled by and caffeine levels are estimates based on both the USDA National Nutrient Database for Standard Reference and information provided by manufacturers.

Caffeine and sleep:

After consumption, caffeine is absorbed by the blood and body tissues within 45 minutes and remains there for about 4 to 6 hours. For this reason, you should set a daily firm cutoff for the consumption of coffee (and other caffeine containing products). Even if you don’t feel the effects of coffee, it can still cause sleeping problems later in the night. It is generally advised to limit coffee intake to the morning hours and stop consumption by 2 pm. If you still crave coffee, you can always order decaffeinated.

How sleep is regulated: why and how we go to sleep and wake up

Why are we awake during the day and sleep at night? Why do you feel more tired as the day progresses? There are two major process involved in regulating the sleep-wake system.

Circadian Rhythm (Biological Clock)

The circadian rhythm uses environmental signals to create a corresponding internal daily rhythm. Circadian process (including sleep, feeding, temperature, and activity patterns) are primarily controlled in the brain by the suprachiasmatic nucleus, a small region within the hypothalamus (Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem., 2006). The main environmental driver of the circadian rhythm is the change in light, since this generally reflects the time of day. Light enters the eye and reaches the retina, which then transmits the light signal to suprachiasmatic nucleus (SCN). The SCN then coordinates the daily cycles of sleep, feeding, activity, and corticosteroid hormone secretion. Exposure to light in the mornings cues the suprachiasmatic nucleus to send signals to increase the body’s temperature and inhibit melatonin- processes that help you wake up. When it gets dark, the suprachiasmatic nucleus decreases core body temperature and instructs the pineal gland to secrete melatonin, a hormone which helps further regulate the circadian rhythm. Lightness and darkness are so important to the circadian rhythm that being exposed to even a small amount of light during the night can suppress melatonin secretion and increase body temperature.

Artificial lighting and electronic devices are new advances in our evolutionary history and our bodies have not yet been able to adapt. Light is composed of many different wavelengths, which are each associated with a particular color. Blue light (which is found in high concentrations in our electronics) adversely affects production of the sleep producing hormone melatonin more than any other wavelength.  By keeping indoor lighting dim at night, wearing blue light blocking glasses at night, using an app like f.lux on computers and tablets, and avoiding looking at electronic screens 2 hours before bedtime, you can combat the adverse effects of blue light at night.

Sleep Homeostasis

Another important biological component of sleep is homeostasis. Homeostasis is generally defined as a collection of processes for an organism to maintain a stable internal environment. When optimal conditions are changed, homeostatic regulatory mechanisms kick in to maintain a balanced equilibrium. Sleeping is a compensatory response to the preceding waking episode. The longer you have been awake, the stronger the drive to fall asleep (Vyazovskiy et al., 2017). Once you fall asleep, the pressure to sleep begins to dissipate until eventually you are likely to wake up. During a waking episode, glycogen (one of the body’s energy sources) is depleted and adenosine (a sleep-regulating neuromodulator) is accumulated in the forebrain, which inhibits the reticular activating system (the part of the brain that keeps you awake). By inhibiting the reticular activating system, the build up of adenosine makes you feel more sleepy (Schwartz and Roth, 2008). In general, the pressure is specific to non-REM sleep (otherwise known as “deep” sleep). After an adequate night containing non-REM sleep, adenosine is removed and you will awaken feeling ready to begin the new day.

Top image credit: Credit: National Institute of General Medical Sciences