Caffeine

The effects from caffeine are felt within 5–30 minutes of having it and can last for 4–6 hours.

Research suggests 400 mg per day is acceptable for most people, but it does depend on your body size and metabolism. The Ministry of Health recommends having no more than 7 cups of tea or instant coffee per day or 3 single shot espresso coffees per day.

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

It's important to know that caffeine content can vary considerably depending on how it's brewed, eg, cold brew coffee can contain a lot more caffeine than brewed (filter or percolated) coffee. This is because in cold brew, coffee grounds are steeped in water for around 8-24 hours. 

Other factors that can affect the amount of caffeine in a cup of coffee include:

• the type of roast, eg, robusta coffee beans may contain twice as much caffeine as arabica
• the amount of ground coffee used during the brewing process
• the serving size.

Pregnant and breastfeeding women, children and athletes

Pregnant women – it’s recommended that you limit caffeine intake to below 200 mg per day during pregnancy and that you avoid energy drinks. Having large amounts of caffeine during pregnancy may increase the risk of miscarriage, stillbirth and having a baby with low birthweight. 200 mg of caffeine is found in 4 cups of tea or 1 espresso.

Breastfeeding women – can drink caffeine in moderation. Some babies may be sensitive and a large amount can cause your baby to be stimulated or have poor sleep. It’s recommended that you limit your caffeine to no more than 6 cups of tea or instant coffee (or 3 single shot espressos) per day.

Children – it’s recommended that children/tamariki are not given tea, coffee or energy drinks as it can affect their sleep or lead to dehydration.

Athletes – some studies suggest caffeine ingestion prior to exercise can improve performance and focus for athletes. Consult with your GP if you're taking caffeine supplements regularly, do not exceed the recommended limit of 40 mg per day and be aware of the side effects.

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
• increased blood pressure
• anxiety and/or panic attacks which can be triggered or made worse
• dehydration ‒ caffeine is a diuretic, meaning it makes your body lose more water, so drinks that contain caffeine are not good if you are thirsty, exercising or working in the heat
• interactions with some medicines. Check with your pharmacist or doctor to see if the medicines you are 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 take larger amounts to achieve the same results. If you are dependent on caffeine and you stop having it, you may experience fatigue, headaches or irritability. The easiest way to break caffeine dependency is to gradually reduce the amount you’re having. It may take between 1 and 7 days.

To curb your caffeine habit, try decaf tea or coffee, or herbal teas that don’t contain caffeine.

Caffeine overdose is dangerous and can be fatal:

• There is a reported case of a 19-year-old college student who died after taking an overdose of caffeine tablets to stay awake.
• Caffeine doesn't reduce breath or blood alcohol concentrations, so it doesn't get rid of the effects of alcohol.
• Mixing alcohol with energy drinks is dangerous as the caffeine hides the depressant effects of alcohol. As a result, you may drink more alcohol and become more impaired than you realise.