Caffeine

Caffeine is a mild stimulant which affects your brain, heart and gut. A small amount can help you feel more awake and clear minded and can help you concentrate better. However, large amounts can make you feel anxious, increase your heart rate and lead to sleeping difficulties. 

Caffeine is present in more than 60 plants including kola nuts, cocoa beans, coffee beans, tea leaves, guarana and yerba mate. The caffeine in chocolate comes from cacao or cocoa beans, and the caffeine in cola drinks comes from kola nuts. 

Caffeine is added to many soft drinks and energy drinks. Some snack, muesli or sports bars may have cacao or guarana added, so they can contain caffeine too – always check the label. Matcha and kombucha are made of tea, so they contain small amounts of caffeine. 

Caffeine is sold as capsules or tablets. It’s also used in some migraine medicines, and for premature babies to help with breathing.

Caffeine stimulates your brain. It blocks receptors for a type of neurotransmitter (chemical messenger) called adenosine. This is what causes the feeling of wakefulness, energy and focus. 

You also have adenosine receptors in your muscles, which is why caffeine can make your heart beat harder and faster. It’s also why caffeine can improve muscle strength and endurance, particularly in men.

It releases adrenaline, which stimulates the rest of your body too.

Caffeine also affects your blood vessels, including the blood flow to your kidneys. This can make you pee more (diuresis). You make more stomach acid and your gut muscles squeeze more. Caffeine can also make you breathe more deeply.

You feel the effects of caffeine within 5 to 30 minutes. The biggest effect happens between 30 minutes to 2 hours after taking it. The average time the feeling lasts is 5 hours, but this can be very different for different people. It could be only 2.5 hours if you smoke but up to 15 hours if you’re pregnant.

In Aotearoa New Zealand the recommended maximum daily caffeine intake is no more than 400 mg per day from all food and drink sources. People react to caffeine in different ways and the amount of caffeine that is appropriate for you will depend on your individual body size and metabolism. 

Black tea and coffee can benefit health because of properties they contain such as antioxidants. However, they both contain caffeine and tea contains tannins, which lower the amount of iron absorbed by your gut. For this reason, the Ministry of Health recommends drinking only moderate amounts of tea and coffee.

Image credit: MOH, Eating and Activity Guidelines for Adults, 2020

The caffeine content in coffee can vary considerably depending on:

• the type of coffee, eg, brewed coffee may contain anywhere from 95 to 200 mg per cup and instant coffee may contain anywhere from 27 to 173 mg per cup
• the type of beans, eg, robusta coffee beans may contain twice as much caffeine as arabica
• the amount of coffee/beans used in the brewing process
• the number of shots in coffee.

For tea, the amount of caffeine depends on how much water it's brewed in, how long it's brewed for and the quality of the tea. 

Caffeine for people who are pregnant or breastfeeding and for children and athletes

Pregnancy: It takes longer for caffeine to clear from your blood when you're pregnant. It's recommended to limit caffeine intake to below 200 mg per day during pregnancy and to avoid energy drinks and energy shots. Having large amounts of caffeine during pregnancy may increase the risk of miscarriage, stillbirth and having a baby with low birthweight. 

Breastfeeding: Caffeine is transferred to breast milk. Some babies may be sensitive and a large amount can cause your baby to be stimulated or have poor sleep. If you're breastfeeding it’s recommended you limit your caffeine intake to less than 200 mg a day and avoid energy drinks and energy shots. 

Children: Tamariki don't need caffeine from tea, coffee, cola drinks or energy drinks. It's been linked to irritability and can affect their sleep. There is research showing increased anxiety in children who consume about 3 mg of caffeine per kilogram of bodyweight per day. To put that in real life terms, 3 mg of caffeine per kilogram for a child weighing 25 kg would be 75 mg, and a 250 mL energy drink contains 80 mg. 

Athletes: Some studies suggest consuming caffeine before exercising can help to improve performance and focus for some athletes. As a result, caffeine is becoming popular in sport with many different supplements and sports products available. It's important to consult with your healthcare provider before taking any form of caffeine supplement to make sure it's safe and suitable and the risk of side effects is minimised. The maximum limit of 400 mg of caffeine per day should still be followed. 

Some people are more sensitive to the effects of caffeine than others. Signs of having too much caffeine are:

• poor sleep ‒ avoid caffeine after 4pm or earlier
• headaches or dizziness
• fast or abnormal heart beat
• feeling jittery, irritable or shaky
• heartburn ‒ caffeine increases the release of acid in your stomach, sometimes leading to an upset stomach or heartburn
• flushed face
• diarrhoea (runny poo)
• increased blood pressure
• anxiety and/or panic attacks which can be triggered or made worse
• interactions with some medicines (eg antidepressants) – check with your pharmacist or doctor to see if the medicines you're taking could interact with caffeine.  

It’s possible to build up a tolerance to caffeine, so your body gets used to the effects and you may need to consume larger amounts to achieve the same results.

If you consume drinks containing caffeine every day you can become dependant on it. This means if you stop having it, you may experience fatigue, nausea (feeling sick), headaches, irritability or depressed mood. This starts 12 to 24 hours after your last intake of caffeine and is worst after 1 to 2 days. The easiest way to break caffeine dependency is to gradually reduce the amount you’re having. It may take between 1 and 7 days. For example if you drink 6 cups of coffee a day, drink 5 cups on the first day then 4 the next and so on.

To curb your caffeine habit, try decaf tea or coffee, or herbal teas that don’t contain caffeine such as peppermint, camomile, berry, or lemon and ginger.

Note: some herbal teas can be harmful in pregnancy and are only suitable in moderation when breastfeeding. It's always important to read the label. 

Too much caffeine

Caffeine overdose is dangerous and can be fatal. Symptoms of overdose are disorientation, vomiting, hallucinations, psychosis, seizures, abnormal heart rhythms and muscle breakdown. For most people it would take more than 3 times a safe daily dose of 400 mg to get these symptoms.

Caffeine overdose can also cause nausea, diarrhoea, light-headedness and urinary frequency.

• The effects of alcohol on your body don't change when you drink alcohol with caffeine. Caffeine doesn't reduce your breath or blood alcohol concentrations.
• Drinking alcohol that's mixed with caffeine (eg, in energy drinks or coffee) can make you drink more, which could make the effects from alcohol stronger.
• This is because caffeine can 'mask' the effect of alcohol and make you feel more alert and think you can drink more which can be dangerous.
• Other concerns with mixing alcohol and caffeine include:
  • higher blood pressure
  • irregular heartbeat (arrhythmias)
  • losing water from your body (dehydration).
• Because alcohol makes you feel sleepy and caffeine makes you feel awake, consuming them together can mean you don't notice the negative effect they have on the quality and amount of sleep you get.

The Food Standards Code restricts the amount of caffeine that can be added to cola drinks and energy drinks and foods. Foods with added caffeine must also have a statement on the label so it's clear that the product contains caffeine. Foods containing guarana must also be labelled as containing caffeine. This is to help people avoid caffeine either for themselves or their children.

In cola drinks, the total caffeine content mustn't be more than 145 mg/kg in the drink as it's intended to be consumed. In energy drinks, the total caffeine content must not be more than 320 mg per litre. There also needs to be a statement warning that the product isn't suitable for young children, pregnant or breastfeeding women and people sensitive to caffeine. 

Pure and highly concentrated caffeine food products (including pure caffeine powder) are banned from retail sale in Aotearoa New Zealand and Australia. These products are typically bought online and can cause serious health effects and be lethal. 

The products are often marketed as sports supplements and can contain the same amount of caffeine as 25 to 50 cups of coffee in a single teaspoon. It's impossible to safely measure the powder from a bulk packet which means there are risks of having a toxic dose (including death). It's recommended not to purchase or consume these products due to the risks.