Around 1.4 billion cups of coffee are consumed worldwide every day. Its average annual consumption in European Union countries is 5.6 kg per person [1]. Almost 90 per cent of Poles drink coffee every day, and half drink it more than once a day [2]. However, coffee – like virtually every product – is capable of causing allergic reactions. Sometimes even the most severe ones.
Antiallergic or sensitising?
Coffee is a complex mixture of chemicals that acts on the central nervous system. Its main ingredient, caffeine, is the most commonly consumed psychoactive agent [3]. It reaches its maximum effect 30-45 minutes after drinking. It diffuses throughout the body, crosses the blood-brain barrier and temporarily prevents drowsiness [3]. It is found not only in coffee, but also in tea and holly leaves (yerba mate), cocoa beans, guarana berries [3]. One cup of coffee (100 ml) has about 90-120 mg of caffeine. This compares to 70 mg for black tea and 23 mg for a cola drink [12].
The impact of coffee on health is multifaceted. It is constantly subject to research and the conclusions of reports on the subject are often contradictory. This is due to the fact that coffee is not only caffeine, but also:
- polyphenols (chlorogenic acid, lignans),
- alkaloids (trigonellins),
- melanoidins formed during the roasting of the beans,
- small amounts of magnesium, potassium and vitamin B3 (niacin) [3].
These compounds – in the right dose – can reduce oxidative stress, improve the gut microbiome, promote fat and glucose metabolism (and thus reduce the risk of type 2 diabetes) [3,10]. At the same time, however, caffeine is suspected of increasing the likelihood of cancer and cardiovascular disease [2]. In contrast, caffestol (a diterpene), which is present in unfiltered coffee, is suspected of increasing blood cholesterol levels [3].
Coffee drinking vs. allergy and asthma
Researchers in Taiwan decided to test the effects of coffee and caffeine on airway hyperresponsiveness and the occurrence of allergic reactions [4]. What were the conclusions? It turned out that in mice that were regularly given coffee, there was a significant inhibition of the immune system response mediated by Th2 lymphocytes. And it is these lymphocytes that stimulate the development of allergic reactions. In the experimental group, coffee significantly reduced the response of IgG and IgE immunoglobulin specific for ovalbumin (egg white allergen) [4].
Other interesting findings come from the UK. Almost 430,000 participants aged 39-73 years from (from the UK Biobank) were studied. The study found an association between moderate coffee and tea consumption (160-305 mg caffeine/day) and a reduced risk of asthma in adults [5]. There have already been scientific reports that caffeine improves airway function in asthma patients [4,6] and has anti-inflammatory effects [4,7].
Coffee allergy vs. caffeine hypersensitivity
Although coffee appears to have an anti-allergic effect, it is important to remember that it too can be an allergen. It was first identified as a culprit in allergic respiratory diseases in the late 1950s and early 1960s [9].
Coffee allergy is extremely rare, but in isolated cases it has been confirmed by diagnostic tests. Caffeine-induced complaints may indicate an allergy (i.e. an IgE-dependent type I reaction) or a non-allergic hypersensitivity [8].
German scientists detected a coffee allergy in 3 out of 17 individuals experiencing symptoms after contact with this substance [9]. The same scientists also discovered the first known coffee allergen – Cof a 1 (class III chitinase). Importantly, the studied group included individuals involved in coffee bean processing. This proves that coffee can be an occupational allergen. Currently, the percentage of respiratory diseases reported by café workers is increasing [9]. The source of exposure is not so much the beans themselves but rather coffee dust. It can cause symptoms such as conjunctivitis and allergic rhinitis [9].
Unexpected cause of hives
Researchers from Italy presented the case of a woman aged 24 years who struggled with recurrent hives [12]. She presented with blisters located on the lips, neck, hands and feet and in the groin. The skin lesions were accompanied by itching (eyelids, ears and tongue) [12]. The woman’s condition required emergency room intervention on several occasions. Episodes occurred most frequently at work, but also outside work.
A thorough clinical history supplemented with allergy tests established that it was a reaction to caffeine. It turned out that the woman drank a cup of coffee each time before the onset of these symptoms. Researchers speculate that many cases of caffeine hypersensitivity may be misdiagnosed as idiopathic urticaria [12].
Anaphylaxis after coffee
People with coffee allergy can even develop anaphylaxis. This was the case for a 27-year-old woman who experienced a severe reaction after eating a candy containing 42 mg of caffeine. Prior to this episode, she had never had any allergy symptoms. The caffeinated candy caused her to have a pruritic throat, followed by dyspnoea, generalised hives and angioedema (anaphylactic reaction) [13].
Caffeine and medicines – a hazardous mix
Some pharmaceuticals (quinolone antibiotics, cardiac medications, bronchodilators, antidepressants) may slow down the effect of caffeine and prolong its persistence in the blood [3]. Caffeine also affects the action of many drugs, so it must be considered in the context of possible interactions. Due to its opposing effects, it may, for example, reduce the efficacy of sedative and sleep medications [10]. Caffeine’s adverse effects include allergic reactions [10].
Caffeine is the active ingredient in a long list of pharmaceutical products (including those intended for children) [4], which may be responsible for some cases of drug-induced hives [10].
A case is described of a 69-year-old woman who developed generalised hives after taking an over-the-counter analgesic with aspirin, paracetamol and caffeine. The same woman developed hives six more times (each time after drinking one cup of coffee). It was accompanied by:
- itching of the hands,
- swelling of the lips,
- dizziness [8].
Coffee allergy or caffeine overdose?
An adverse reaction to caffeine can be caused not only by an allergy or hypersensitivity, but also by an overdose of this substance. Its excess particularly affects the heart muscle. It causes tachycardia (cardiac tachycardia), increased blood pressure and reddening of the skin [10]. With regular exposure to caffeine in high doses, chronic intoxication occurs [10].
After caffeine – not necessarily due to an allergy to coffee – the following may occur:
- gastrointestinal disorders
- headaches
- muscle tremors,
- insomnia,
- difficulty concentrating [10].
The acceptable (i.e. safe) dose of caffeine according to the FDA (US Food and Drug Administration) is 400 mg per day. However, consumption of 20 mg or more per kilogram of body weight is toxic. At a dose of 150-200 mg per kilogram of body weight, caffeine can cause death [11].
