Caffeine and headaches – what’s new?

How caffeine and headaches interact is among the most common questions asked in the headache community. It’s worth taking a look at the latest research findings and asking what they mean for headache prevention.

The many effects of caffeine

According to various studies, about 80% of the global population regularly consumes caffeinated foods and drinks, many on a daily basis. This is unsurprising, as coffee is known for its stimulating and invigorating effects, as well as its ability to enhance concentration. Additionally, caffeine is believed to have a number of health benefits, including beneficial effects on the cardiovascular system, diabetes, and Parkinson's disease. There are even reports of potential benefits against cancer. However, caffeine can also cause sleep problems, especially when consumed in the evening.

The body absorbs caffeine very quickly, with a bioavailability of nearly 100%. This means that almost all of the caffeine we consume, for example in drinks like tea or coffee, enters our bloodstream and reaches the target sites in our body. A cup of filter coffee contains around 100 mg of caffeine, black tea has about 45 mg, and green tea contains 30 mg. The effect lasts quite a while, as it takes the body four to eight hours to eliminate half of the ingested caffeine.

A key player: adenosine

Adenosine triphosphate (ATP) is the most important energy carrier in our cells (read more about it in this article) and the source of adenosine. When ATP is used up during energy metabolism, adenosine remains as the “end product”.

It’s thought that adenosine accumulates in the body throughout the day and into the evening. Once its levels reach a certain point, we start to feel tired. In this way, adenosine plays a regulatory role in our daily sleep-wake rhythm, acting as a link between our energy balance and nerve activity. Substances that function as messengers in the nervous system are known as neurotransmitters or neuromodulators. These substances control various functions of nerve cells. They do this by binding to specific sites on the target cells, known as receptors. Receptors act like switches that activate various processes.

Caffeine is an antagonist of adenosine

This is where caffeine comes in. Caffeine has a very similar chemical structure to adenosine and can compete with it for receptor binding – but without exerting the corresponding regulatory functions. When caffeine docks onto a certain proportion of the binding sites, the actual messenger substance can no longer bind in sufficient amounts, and fails to take effect. This helps explain why caffeine can partially and temporarily reduce adenosine’s sleep-inducing effects. We perceive this effect as a “wake-up” boost, making us feel (or at least appear) more alert and focused than we would without caffeine.

Caffeine and headaches

While there are numerous studies on the effects of caffeine on headaches, their results vary widely. The reasons for these discrepancies lie in the details. Our body has at least three different types of adenosine receptors. As a result, the actual effect of adenosine – and that of caffeine, its antagonist – depends crucially on the type of signaling pathway where binding occurs, how extensively binding happens, and how interactions between the receptors play out. This leads to a wide range of variations amid changing conditions.

It was previously thought that caffeine causes blood vessels to constrict, thereby reducing blood flow in the brain. This was presumed to underlie the pain-relieving effect reported by many migraine sufferers. However, it is now known that the constriction of blood vessels is not directly linked to this perceived benefit. The processes that regulate blood flow in the brain are much more complex than previously thought. Current theories suggest that caffeine’s effects can vary depending on whether it is consumed regularly or sporadically. Research has had to begin again almost from scratch in this respect. It is possible that the contradictory results stem from different signaling pathways: some that relate to the competition with adenosine for receptors, and others that have a direct effect on blood vessels.

Adenosine and migraine aura

Some migraine sufferers with aura experience fatigue and extreme tiredness in the run-up to an attack. Adenosine may also play a role here. Experimental studies have shown that administering adenosine can trigger migraine headaches. The ability of caffeine to prevent or at least alleviate such pain attacks can be seen as indirect evidence of its effectiveness as an adenosine antagonist.

What are the recommendations based on research so far?

Research into caffeine’s impact on headaches has made significant strides in recent years. However, it doesn’t provide hands-on recommendations for everyday coffee or tea consumption. For those who find relief from headaches through caffeine, there’s no reason to stop; moderate consumption of caffeinated products appears to be perfectly fine. Some studies even report that it has mostly positive health effects. Recommended limits issued by the relevant institutions apply during pregnancy and breastfeeding.

As far as sweetened caffeinated drinks and energy drinks are concerned, recent studies advise caution. These drinks tend to be high in sugar and may cause more harm than the short caffeine boost is worth.

While the exact mechanisms by which caffeine influences headaches are not fully understood, clinical experience suggests that irregular caffeine consumption can trigger migraine attacks in migraine sufferers. Many report an increase in attacks if they deviate from their usual caffeine habit. One common trigger seems to be abrupt discontinuation of workday coffee consumption on weekends, for instance when the first cup on a Sunday is drunk much later than usual and is not followed by several more cups throughout the day. Medical research so far seems unable to provide a coherent explanation for why fluctuations in caffeine intake may promote migraine attacks. However, if this is a factor for you, try to maintain a similar caffeine consumption pattern every day of the week – including weekends and holidays.