Cigarette smoking increases coffee consumption: findings from a Mendelian randomisation analysis

Marcus Munafò and his colleagues at the University of Bristol, have looked into the smoking and drinking habits of about 250,000 people. They found that smoking makes you drink more caffeinated drinks, possibly by changing your metabolism so that you break down caffeine quicker, pushing you to drink more to get the same hit.

It’s impossible to do a randomised controlled trial (the most rigorous kind of scientific trial) when it comes to smoking, because it would be unethical to ask a randomly selected group of people to smoke. The next best thing is to study huge biobanks of health data. These biobanks contain information about people’s genes, diets and lifestyles.
coffee-cigarettes-smoking-400x400.jpgTo explore the relationship between smoking and caffeine, Munafo and his colleagues analysed data from biobanks in the UK, Norway and Denmark. They were particularly interested in people who had inherited a variant of a gene that has already been shown to increase cigarette smoking.

Chain drinking

The team found that people who had this gene variant also consumed more coffee – but only if they smoked. British people with the same variant also drank more tea, although their Danish and Norwegian counterparts didn’t. This is probably due to cultural differences, says Munafò. “People in Norway and Denmark don’t chain drink tea in the same way that people in the UK do,” he says.

The genetic variant seems to influence how much nicotine a person consumes. You can have zero, one or two copies – and each additional copy is linked to an increase in smoking of about one cigarette per day. Each copy also appears to increase coffee consumption by 0.15 cups per day.

“You could extrapolate from that and say that if you smoked 10 cigarettes per day more than the next person, you would be drinking the equivalent of about one and a half extra cups of coffee per day,” says Munafò. He is wary of doing so, though, because the amount of nicotine a person gets from a cigarette will depend on the type of cigarette and the way it is smoked.

The gene variant codes for a nicotine receptor, which is not known to directly interact with caffeine. This suggests that cigarette smoking increases caffeine consumption and not the other way around.

“The team have used a rather clever technique to establish causality, which normally you wouldn’t stand a cat in hell’s chance of doing with an epidemiological study,”

Robert West – University College London.

What’s the link?

There’s a chance that cigarette smoking and caffeine consumption are linked through habit – that smokers tend to pair the two. But Munafò thinks that the nicotine in cigarettes might also influence the way a person metabolises caffeine. “It’s possible that smokers metabolise caffeine more quickly,” he says. If that is the case, smokers might need to consume more caffeine to get the same effects that a non-smoker would experience.

It’s also possible that the apparent link between smoking and coffee drinking could be down to some unknown function of the genetic variant, says West. “It evolved for a purpose, and it wasn’t to smoke,” he says.

A relationship between smoking and coffee might make it harder for smokers to quit, says Munafò. If a smoker stops smoking, but continues to drink plenty of coffee, they might start to experience unpleasant side effects, such as jitteriness. This might be misinterpreted as a symptom of smoking withdrawal, says Munafò. His team plans to investigate this.

By Jessica Hamzelou

Journal reference: bioRxiv, DOI: 10.1101/107037

Report launch: New issues and age-old challenges: a review of young people’s relationship with tobacco | 27/02/17


Join Prof Amanda Amos and Prof Marcus Munafo to discuss the current landscape, challenges and opportunities including a focus on young people, tobacco and mental health.

Please book your free please here>

The face of youth smoking in the UK is evolving.  Young people are growing up in a society radically disrupted by new technologies and societal norms, which are reshaping their perceptions of personal health, image, and values.

New issues and age-old challenges: a review of young people’s relationship with tobacco, brings together the available evidence on youth smoking and articulates a clear demand for action across the system.

Martin Dockrell from Public Health England will chair the panel session.

Full agenda is available here>

Electronic cigarettes could have a huge effect on public health | Marcus Munafo, University of Bristol

June 20, 2016 2.17pm BST – Marcus Munafo – The Conversation

Tobacco still kills 6m people around the world every year. Despite huge public health efforts to help people quit and prevent young people starting, smoking remains the single greatest cause of ill health and premature death. And even with restrictions on tobacco advertising and smoking in public places, many young people continue to take up smoking. The situation is even worse in poorer countries, where support to stop smoking is limited, and tobacco control policies weaker.

So in light of this, how should we view the increasing popularity of electronic cigarettes?

image-20160620-8853-1qda1qwThe gadgets deliver a nicotine hit by heating a nicotine-containing propylene glycol (e-liquid) to create an aerosol (usually called “vapour”), which is inhaled. Put simply, they deliver nicotine almost as effectively as a conventional cigarette, but without the vast majority of other chemicals present in tobacco smoke (either from the tobacco itself, or as a result of the burning process).

A whole culture is emerging around “vaping”. Many devices offer a range of power settings, and a vast array of e-liquids is on offer, with varying nicotine contents and flavours. Enthusiasts often apply modifications to their devices, and engage in “cloud chasing” – competing to produce the largest and most interesting clouds of vapour. And yes, young people are experimenting with e-cigarettes (in the same way that they have always experimented with pretty much everything), although at the moment there is no strong evidence this is leading to subsequent cigarette use, or even long-term e-cigarette use.

The rapid growth in use of e-cigarettes, especially among smokers trying to cut down or quit, has taken the public health community and the tobacco industry by surprise. Both are struggling to catch up. Health professionals are hurrying to carry out research to develop evidence-based guidelines and policies. Meanwhile, the tobacco industry is buying up e-cigarette companies and introducing its own products onto the market.

So how concerned should we be about this emerging and disruptive technology?

Should we encourage existing smokers to use e-cigarettes to help them stop smoking, even if this means they continue using nicotine long-term? In the United Kingdom there is some consensus that smokers should be encouraged to use e-cigarettes if they feel they might help, and the National Centre for Smoking Cessation and Training is supportive of their use. Part of the reason many vapers feel so passionately about the subject (and react strongly when they feel that vaping is being unfairly attacked) is that for the first time, through the use of e-cigarettes, they have felt able to take control of their nicotine habit, stop smoking, and reassert some control over their health, without being medicalised in the process.

But a problem remains in the lack of information on the possible harm of e-cigarettes. This is unlikely to change any time soon, since the health effects of tobacco use can take several decades to emerge, and it’s probable the same will be true for e-cigarettes. Nothing is entirely risk-free, but the vastly reduced number of chemicals present in e-cigarette vapour compared to tobacco smoke means we can be confident that vaping will be much, much less harmful than smoking.

Heartening evidence

As part of the investigation into the effects of e-cigarettes, we investigated how the cells found in the arteries of the heart, known as human coronary artery endothelial cells, responded when they were exposed to both e-cigarette vapour and conventional cigarette smoke. We found the cells showed a clear stress response from the cigarette smoke, but not from the electronic cigarette. This suggests tobacco smokers may be able to reduce immediate tobacco-related harm by switching from conventional cigarettes to e-cigarettes.

Many people find it difficult to function without their first caffeine hit of the day. But no one is seriously calling for coffee shops to be dismantled or regulated. Nicotine is addictive, but much less so on its own than in tobacco, where other chemicals enhance its effect. At the doses consumed by vapers the harm is likely to be very low (although we need to continue to research this), and many vapers actually gradually move to zero nicotine content e-liquids, even while continuing to vape.

Of course, we may end up with a large population of long-term nicotine users who use e-cigarettes to deliver nicotine rather than cigarettes, but all of the evidence at the moment suggests that this population will almost entirely comprise ex-smokers. This would produce a vast public health gain.

We must be careful not to restrict smokers’ access to e-cigarettes, or over-state the potential harm of their use, if this will put people off making the transition from smoking to vaping. To do so would deny us one of the greatest public health improving opportunities of the last 50 years.

Original post – The Conversation | More on E-cigarettes from UKCTAS