Coffee & Caffeine Consumption

How does caffeine work?

When we are tired, our bodies create adenosine, a chemical that attaches to nerve cells and causes them to slow down. Caffeine interrupts this process by attaching to nerve cells and blocking adenosine from attaching. As a result, our nerve cells do not receive the signal that it is ‘time to slow down’. At the same time, norepinephrine and dopamine, which act as stimulants in the brain, are produced by our pituitary gland and increase our heart rate, dilate our blood vessels to increase blood flow, and ultimately increase brain activity [1] Jump to reference section: [1] .

Caffeine is naturally occurring and found in coffee, tea, and even chocolate in small amounts. Coffee has the highest caffeine content by far, with 200 - 400 milligrams in an average serving. A cup of black or green tea, has 50 - 150 milligrams and a half a bar of chocolate has about 40 milligrams.

Over time, regular coffee or tea drinkers can become less affected and can even form a physical dependence. This is why regular coffee or tea drinkers can have a headache or feel grumpy when they are deprived of their morning cup.

How does genetics impact caffeine consumption?

We all have different habits when it comes to caffeine consumption. Genetics has a role to play in these habits by affecting the way our body processes caffeine, and the structure of adenosine receptors in our nerve cells.

Two of the strongest genetic associations with caffeine intake affect enzymes (A substance, often a protein, that helps to speed up a chemical reaction. In this case, metabolism.) that help metabolise caffeine.

The first genetic association is in ‘cytochrome P450 1A2’ (CYP1A2) and the second is to the ‘aryl‐hydrocarbon receptor gene’ (AHR gene) [2] Jump to reference section: [2] .

CYP1A2 is the enzyme responsible primarily for metabolizing caffeine, and there are genetic variants that increase and decrease its level of activity. The genetic variant rs2472297 has been linked to increased coffee consumption - see what variant you have at this position below:

The AHR gene does not process caffeine directly, but instead works by controlling the level of CYP1A2.

While these genetic variants have been strongly associated with caffeine consumption, they are far from the whole picture. Genetics studies on twins have suggested that caffeine consumption has a highly heritable component - estimates suggest 30-50% of the variation in coffee consumption in a group of people can be explained by genetics. However, in a study looking at coffee and tea drinking habits of nearly 50,000 people, less than 1% of the genetic effects on coffee consumption could be predicted [3] Jump to reference section: [3] .

The bigger picture - how our bodies break down other chemicals

The genes that are involved in caffeine metabolism such as CYP1A2 and AHR are also involved in metabolising other chemicals including pharmaceuticals used to treat disease. As a result, different people may respond differently, or require different doses of medication. The fact that we still do not understand the impact of genetics on caffeine metabolism, even with its massive worldwide adoption, means that there is still a lot of work to be done before we can fully understand individual response to the hundreds to thousands of other chemical compounds we consume every day.