Caffeine is a natural stimulant found in tea, coffee, chocolate and some herbal tea blends as well as in caffeinated, fizzy drinks such as cola. While there is no evidence that caffeine causes persistent high blood pressure, it does cause blood pressure to rise temporarily and some people with hypertension should limit their intakes.
How does caffeine affect your BP?
Caffeine is a stimulant that mimics the effects of stress in the body. It speeds up your heart rate, boosts your metabolism and either causes blood vessels to constrict or blocks a hormone needed for blood vessels to dilate. Researchers still aren’t sure exactly which! These effects cause your blood pressure to increase – sometimes dramatically – even in people who don’t have high blood pressure, although the effect is temporary.
How strong is the effect?
Research published by the American Heart Association looked at the effects of caffeine on arterial blood pressure in 182 men. These included 18 men with known hypertension (and on treatment) but the others were found during health screening sessions and included men with optimal blood pressure (less than 120/80 mmHg), normal blood pressure (120-129/80-84 mmHg), high-normal blood pressure (130-139/85-89 mmHg) or stage 1 hypertension (140-159/90-99 mmHg) based on their resting BP.
Volunteers had their blood pressure measured after 20 minutes of rest, then drank an average dose of 250mg caffeine, based on their weight. Their blood pressure was then measured again after 45 to 60 minutes and the researchers found that caffeine significantly raised both systolic and diastolic in all groups. The strongest response was in the men with diagnosed hypertension, followed by those with stage 1 and high-normal blood pressure, then those with a normal or optimal BP. The effects were striking.
- In men with hypertension, caffeine caused their blood pressure to increase by 10/8 mmHg.
- In men with stage 1 (untreated) hypertension or high normal BP, readings rose by 8/7 mmHg.
- In men with optimal or normal BP, their readings rose by 6/5 mmHg.
This effect lasted for at least one hour. Current guidelines suggest that you refrain from smoking or ingesting caffeine for 30 minutes before your blood pressure is measured, but this study suggests you should perhaps refrain for longer. Otherwise, your doctor may be inclined to increase your blood pressure medication or add in a new treatment.
Other studies have found that the effects of caffeine are also stronger in people who have the most risk factors for heart disease – those who are overweight, smoke, have diabetes, raised cholesterol or are aged 70 years or more, for example.
How to assess your caffeine sensitivity
Some people are more tolerant to the blood pressure raising effect of caffeine due to the genes they have inherited.
If you aren’t sure how caffeine affects you, it’s a good idea to measure your blood pressure with a home monitor before drinking a cup of coffee (or other caffeinated drink); then measure it again after 20 minutes, 40 minutes and 60 minutes. If your blood pressure is still raised, keep measuring it every 20 minutes to see how long the effect lasts.
If your systolic blood pressure (the top number) goes up by at least 5 mmHg then you are sensitive to the effects of caffeine. If caffeine increases your blood pressure significantly, it may be a good idea to cut back and think about whether or not to avoid it altogether.
How much caffeine is OK?
The European Food Safety Authority (EFSA) recently advised that intakes of up to 400mg caffeine a day should have no consequences for healthy adults. Drinking more than this ‘could be damaging’ to health – even for people without high blood pressure. For women who are pregnant or breast-feeding, EFSA advised a lower intake of no more than 200mg caffeine a day.
It’s important to assess your own blood pressure response to caffeine to decide whether this level is OK for you. If you are unsure, or your blood pressure is not well controlled, ask your doctor if you should limit the amount of caffeine you consume. You may be advised to limit yourself to just one caffeinated drink per day, or to avoid it altogether.
Are there any health benefits?
According to the BMJ journal, Heart, moderate coffee drinking is associated with a lower risk of hardening and furring up of the arteries (atherosclerosis). Those who drink from one to five cups of coffee per day appear to have significantly lower levels of calcium build-up, even after taking other factors such as age, smoking status, alcohol intake, body mass index, blood pressure, diabetes and cholesterol levels into account.
How to assess your caffeine intake
Average caffeine intakes are between 200mg and 300mg per adult per day. The amount of caffeine in a cup of tea or coffee varies widely from 30 mgs to 150 mgs as the level of caffeine extracted from coffee beans and tea leaves increases the longer it brews. Cups also vary in size – a standard coffee cup holds 125ml. Typical sources of caffeine are as follows:
- 60ml espresso provides around 80mg caffeine
- 125ml cup of instant coffee provides 65mg caffeine
- 125ml cup of filtered coffee contains 85mg caffeine.
- 150ml cup of tea provides 32mg caffeine
- 250ml standard can of energy drink provides around 80mg of caffeine (check labels)
- 330ml can of cola provides around 40mg (check labels).
There’s between 25mg and 50mg caffeine in a 50g bar of plain chocolate (the darker the chocolate, the stronger it is) and 10mg caffeine in a 50g bar of milk chocolate.
Caffeine is also found in many over-the-counter drugs, especially those designed to treat headaches and colds. High strength caffeine tablets are taken by some people to help them keep awake and alert eg when studying for exams – these are definitely best avoided if your blood pressure is raised!
If you are used to a regular caffeine intake, cut back slowly at first by a half to one cup per day. Otherwise you may develop caffeine withdrawal symptoms of headache, irritability, fatigue and lethargy.
Swap caffeinated drinks for decaffeinated brands of tea, coffee and carbonated drinks. If you prefer to continue using caffeinated versions, make your drinks less strong by brewing them for a shorter length of time or adding less coffee granules/grounds or tea leaves.
For more information, see How Much Caffeine In Your Coffee?
If your blood pressure is borderline or raised, self-monitoring is key to maintaining good control.
Click here for advice on choosing a blood pressure monitor to use at home.