Doctor explains what happens when you drink coffee later in the day: ‘Reduces sleep quality, not just sleep duration…’

Doctors often advise keeping your coffee intake restricted to the morning, because the caffeine can interfere with sleep. Dr Sood explains what really happens.

If coffee is a non-negotiable part of your daily routine and your mornings don’t quite begin without that caffeine kick, you’ve probably also heard experts suggest cutting it off by mid-afternoon – often around 3:00 pm. There’s solid science behind that advice. Consuming coffee later in the day means caffeine lingers in your system well into the evening, often overlapping with your natural wind-down time. And its impact goes beyond just making it harder to fall asleep!

Dr Kunal Sood, an anaesthesiologist and interventional pain medicine physician, is breaking down the impact of consuming coffee later in the day, explaining how it can interfere with sleep quality and disrupt the body’s natural rest-and-recovery cycle.

In an Instagram video shared on March 27, the physician highlights, “Late caffeine shifts the brain into a more alert state at the wrong time. It alters sleep architecture, stress hormones, and next-day recovery. It reduces sleep quality, not just sleep duration, which is why you can sleep ‘enough’ but still feel tired.”

Harder to fall asleep

According to Dr Sood, caffeine works by blocking adenosine receptors – the signals that normally tell your brain it’s time to feel tired – thereby disrupting your natural sleep drive. What makes this more problematic is how long caffeine lingers in the body; it can stay active for over six hours after consumption, interfering with your brain’s ability to recognise when it’s time to wind down and sleep.

The physician explains, “Caffeine blocks adenosine receptors, preventing the buildup of sleep pressure. This increases sleep latency and delays the brain’s recognition that it is time to sleep. Effects can persist even when caffeine is consumed up to 6 hours before bedtime.”

Reduced deep sleep

Dr Sood further highlights that adenosine plays a key role in regulating deep, restorative sleep. When caffeine levels remain high in the body, this process is disrupted, reducing the amount of deep sleep you get and increasing time spent in lighter, less restorative sleep stages.

He explains, “Adenosine also regulates slow-wave activity, the most restorative stage of sleep. Caffeine reduces slow-wave (deep) sleep and increases lighter sleep stages. Systematic reviews show measurable reductions in deep sleep with increased light sleep.”

More nighttime awakenings

According to the physician, caffeine also ramps up sympathetic activity – keeping your body in a more alert, “fight-or-flight” state even when you’re trying to rest. This heightened alertness can make you more prone to waking up during the night, leading to fragmented, less restorative sleep.

He notes, “Caffeine increases neuronal activity and sympathetic tone, creating physiologic hyperarousal during sleep. This leads to more wake after sleep onset and lower sleep efficiency, meaning sleep becomes more fragmented.”

Raises cortisol

Dr Sood also points out that caffeine stimulates the release of cortisol – the body’s primary stress hormone – which heightens alertness. This prolonged state of wakefulness can make it harder to fall asleep and may contribute to sleep difficulties.

He elaborates, “Caffeine stimulates the HPA axis and increases cortisol secretion. Because cortisol promotes wakefulness, elevated evening levels can further impair the ability to initiate and maintain sleep.”

Next-day fatigue

Even if you manage to fall asleep and clock a full night’s rest, the physician notes that the quality of that sleep may still be compromised. With reduced deep sleep and more fragmented sleep cycles, the body’s ability to recover is impaired – leaving you feeling unrefreshed and fatigued the next day.

Dr Sood explains, “Even if total sleep time appears adequate, reduced deep sleep and fragmented sleep impair recovery. Studies link caffeine-related sleep disruption to next-day fatigue, reduced performance, and continued reliance on caffeine.”

Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. It is based on user-generated content from social media. HT.com has not independently verified the claims and does not endorse them.