Energy drinks and coffee to study late: what about sleep?

Coffee or an energy drink during a late study session may make it hard to fall asleep when you meant to. MedlinePlus, from the US National Library of Medicine, says caffeine reaches its peak level in the blood within 1 hour and that you may feel its effects for 4 to 6 hours, and the US National Heart, Lung, and Blood Institute (NHLBI) says the effects can last up to 8 hours. So a coffee at 10 p.m. may still be working when you want to sleep. This is common among Thai students: in a survey of 2,854 college students, 58.0% used stimulant drinks, and using them was linked to poor sleep quality. The US CDC advises avoiding caffeine in the afternoon and evening, and the US FDA cites 400 mg a day as an amount not generally associated with negative effects for most adults, though sensitivity varies from person to person.

If exam worry is what keeps you awake, see Too stressed to sleep before exams? How can you relax?. For feeling sleepy through the day, see Always sleepy during the day? Why, and what can I do?

How common are energy drinks and coffee among Thai students?

Several Thai studies have asked students and working-age adults about caffeine. They show it is part of everyday life for many people.

What Thai studies found

What these numbers can and cannot tell us

All three are surveys at one point in time, with people reporting their own drinking and sleep. They show that caffeine use and poor sleep often go together, but not which comes first: people who sleep badly may drink more caffeine to stay alert, and caffeine may also make sleep worse. The student studies were published more than ten years ago, and the rural study covers adults outside cities, so today's figures in Bangkok universities may differ.

How long does caffeine stay with me after I drink it?

Longer than most people expect. That is why a drink in the evening can still matter at bedtime.

What health agencies say

A study on caffeine timing

A US study by Drake and colleagues gave people 400 mg of caffeine at bedtime, 3 hours before bed or 6 hours before bed, and compared each with a placebo while measuring their sleep at home. All three timings disturbed sleep. The authors wrote that the results support the common advice to avoid substantial caffeine for at least 6 hours before bedtime. The study used a single 400 mg dose, which the authors called a moderate dose, and its timing advice matches the public guidance above.

How much caffeine is in coffee, tea and energy drinks?

The amount varies a lot, even between drinks that look alike.

Typical amounts

These are US figures. Drinks in Thailand come in many sizes, and iced coffee from a shop can be stronger or weaker than these ranges. MedlinePlus also notes that the amount of caffeine in energy drinks can vary widely and that labels do not always give the actual amount.

The daily amount for most adults

For most adults, the US FDA cites 400 mg a day, about two to three 12-ounce cups of coffee, as an amount not generally associated with negative effects. How much is too much varies with body weight, medicines and how sensitive a person is.

Children and teens

The US FDA says medical experts advise against energy drinks for children and teens, because of their sugar and caffeine. MedlinePlus lists children and teens, and people who are pregnant or breastfeeding, among those who should check with a health care provider about whether to limit or avoid caffeine. The US CDC recommends 8 to 10 hours of sleep a day for teens aged 13 to 17.

What are the signs of having too much caffeine?

Late-night study sessions can add up to more cups than usual.

Signs listed by the US FDA

The US FDA lists an increased heart rate, heart palpitations, sleep disruption, anxiety, jitters, an upset stomach, nausea and headache as signs that you may have had too much caffeine.

Mixing with alcohol

MedlinePlus says it is dangerous to combine alcohol and caffeine, because caffeine can interfere with your ability to recognise how drunk you are, which can lead you to drink more. Energy drinks mixed with spirits at parties after exams are one example.

Cutting back

If you drink caffeine every day and want to cut back, the US FDA says it is best to do so gradually. MedlinePlus says stopping regular caffeine can bring headaches, drowsiness, irritability, nausea and trouble concentrating, which usually pass within days.

How can I study late without losing too much sleep?

Studying late is sometimes unavoidable. The general sleep advice for everyone still applies on these nights.

Protect the hours you need

The US CDC recommends 7 or more hours of sleep for adults aged 18 to 60, and advises going to bed and getting up at the same time every day. If you know a heavy week is coming, try to move study time earlier in the day so it does not eat into those hours.

Watch the timing of drinks

If you drink coffee, tea or energy drinks, the CDC and NHS advice is to keep them to the earlier part of the day. Iced tea and cola count too, as they also contain caffeine.

Short naps and daylight

The NHLBI advises adults to nap for no more than 20 minutes, and to spend time outside every day when possible and be physically active. For more on nap length and timing, see How long should a nap be, and when?

Late nights and daytime sleepiness often go together

In the Thai student study by Tran and colleagues, energy drink users were more likely to report daytime sleepiness and to be evening types. It was a one-time survey, so it cannot tell which came first. For some people, a late night may lead to a sleepy day, more caffeine the next afternoon and another late night. The CDC's advice to keep the same wake time every day applies on these days too.

When should I talk to a doctor or pharmacist?

Ask for advice if caffeine or sleep problems are affecting your daily life.

About sleep

England's NHS advises seeing a doctor if changing your sleep habits has not helped, if you have had trouble sleeping for months, or if it affects your daily life in a way that makes it hard to cope. It also advises not driving when you feel sleepy.

About caffeine and medicines

MedlinePlus says some medicines and supplements can interact with caffeine. If you take any medicines regularly, or are pregnant or breastfeeding, ask a doctor or pharmacist about caffeine.