Oliver Wendell Holmes, Senior
The morning cup of coffee has an exhilaration about it which the cheering influence of the afternoon or evening cup of tea cannot be expected to reproduce.
By some estimates, caffeine is the most widely-used drug in the world, with about 1.6 billion cups of coffee alone served on a daily basis. In the U.S., roughly 85 per cent of the adult population consumes at least one caffeinated beverage each day.
The fact, then, that more than 10,000 scientific articles on caffeine have been published should come as a surprise to no one.
In the literature, there is mixed evidence regarding the health effects of consuming caffeine. The chemical may confer protective effects against cancer, neurodegenerative disorders, and type 2 diabetes, but might also contribute to bone loss and heightened levels of anxiety.
Nonetheless, for those of us who indulge in coffee, science has much to say about the best practices surrounding when and how to consume caffeine.
In this first piece, I synthesize the available research regarding the timing of caffeine consumption, which elicits some surprising advice.
Disclaimer: This piece is for general informational purposes only and does not constitute the provision of health care services, including the giving of medical advice. The use of information on this blog or materials linked from this blog is at the user’s own risk. The content of this blog is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Users should not disregard, or delay in obtaining, medical advice for any medical condition they may have, and should seek the assistance of their health care professionals for any such conditions.
When to Drink Coffee
The First Cup
Perhaps the two worst times to consume caffeine are immediately before getting into bed at night and directly after getting out of bed in the morning.
Shortly after waking up, most healthy individuals experience a 50 per cent boost in levels of cortisol, a stress hormone that contributes to physical and cognitive alertness in preparation for daytime activity, in what is called the cortisol awakening response (CAR).
Cortisol peaks at about 30 to 45 minutes after waking up and returns to levels comparable to those at awakening after about an hour.
Caffeine, meanwhile, reaches its peak concentration in blood plasma about 30 to 60 minutes after consumption, although for some individuals, this level might not be reached until 120 minutes post-consumption.
While high levels of caffeine won’t necessarily interfere with CAR, a key tenet of clinical pharmacology is to only use a biologically active agent when necessary. If cortisol already provides the alertness desired upon rising in the morning, why bother drinking a cup of coffee and risking over-stimulation?
For a more advantageous use of caffeine, we should instead aim to consume our first cup of coffee about 30 minutes after waking.
Caffeine will then reach its peak plasma concentration after the cortisol awakening response has occurred. This timing is thereby likely to contribute to more sustained levels of alertness throughout the morning.
The Second Cup
For those who regularly consume caffeine, the first cup of coffee or tea is rarely sufficient to bring about the level of alertness to which they’re accustomed. (Indeed, a tolerance to caffeine may develop after just three to five days of use in humans.)
Provided there are no high-valence stressors presented, cortisol levels gradually decline throughout the course of the day following their peak during CAR.
This drop in cortisol, however, is not a major source of the dreaded feeling of early afternoon drowsiness, which occurs between the hours of 2pm and 4pm for most adults.
The National Sleep Foundation cites four important contributors to this 2:30 feeling:
- Rapid decline in blood glucose levels following a spike from a meal replete with simple carbohydrates
- Neglecting to move for a prolonged period of time
- Mild dehydration
- Drop in body temperature, as per one’s natural circadian rhythm
As noted above, the use of caffeine helps to bolster wakefulness and attention, potentially moderating the effects of the afternoon lull, as well as increase core body temperature, which is also correlated with improved working memory and subjective alertness.
Should none of the other practices be effective, consuming another cup of coffee around noon might help to abate the afternoon slump in cognition.
Given the latency of about 30 to 45 minutes for caffeine to reach its peak plasma concentration, this timing allows for its stimulatory effects to directly abut that feared bout of afternoon drowsiness.
Harmful to the Last Drop: Caffeine and Sleep
While a third cup of java might be tempting as a late afternoon pick-me-up, I vehemently advise against it. The half-life of caffeine, the length of time needed to remove one-half of a given amount of an active substance, is about six hours.
In turn, the quarter-life of caffeine is roughly twelve hours. If you consume your second cup of coffee at noon, which on average contains 100mg of caffeine, you can expect about 25mg to be present in your system come midnight.
The threshold for improved auditory and visual vigilance may be as low as 32mg of caffeine, suggesting that some residual effects of a single cup of coffee may be experienced nearly twelve hours post-consumption.
In another study, consuming 200mg of caffeine (the average content of two cups of coffee) sixteen hours before the onset of sleep led to a significant decrease in total sleep time and efficiency, as measured by EEG.
Other work suggests that higher daily caffeine consumption (about 200mg, on average) contributes to shorter sleep length and lower sleep quality, with the most pernicious effects observed with higher doses of caffeine (400mg) administered within an hour of sleep onset, including prolonged latency to fall asleep, reduced overall sleep duration, and diminished sleep efficiency.
Caffeine abstinence, meanwhile, is associated with a longer duration of time spent asleep and higher quality of sleep.
Should these findings bring you pause, consider drinking green tea or black tea, which contain 35 and 60mg of caffeine, respectively, in lieu of coffee in the afternoon.
This reduction in caffeine consumption should allow for fewer disruptions to one’s sleep.
Alternatively, this additional dose of caffeine can be skipped altogether, a prudent choice to make when placing a premium on sleep.
Although caffeine has been shown to restore vigilance and alertness in sleep-deprived individuals, but no means is caffeine a substitute for obtaining a sufficient amount of rest, which for healthy adults of all ages is more than seven hours per night.
When sleep is restricted to as few as six hours, the cortisol awakening response is observed to be markedly subdued, contributing to excessive sleepiness upon rising. Immediate exposure to bright light, however, might help to elevate cortisol levels and compensate for this diminished response.
Whether one chooses to consume additional caffeine or utilize sources of bright light upon waking, there are absolutely no shortcuts to obtaining enough sleep.
In a forthcoming piece, I plan to detail the ravages of sleep deprivation, which include an increased risk of hypertension, type 2 diabetes, acute myocardial infarction, high cholesterol levels, depression, cancer, Alzheimer’s disease, and suppressed immune system functioning, all but negating whatever protective health effects caffeine consumption might offer.
In the next post in this series, we’ll explore what science can tell us about the best route of consumption and how to maximize the effects of the one or two cups of coffee we do choose to drink.
Here’s to your health!