One afternoon in the summer of 2019, I began to feel an annoying flicker in the corner of my eye, which intermittently stopped and started. It took me a few minutes to realise that one of my eyelashes was twitching.
I’d recently turned 30 and thoughts swiftly flooded through my head – was this a sign of excessive screen time? The early symptoms of some hideous disease? And then I realised that over the past week, I’d been regularly drinking three cups of particularly strong coffee. Following a subsequent week-long “caffeine holiday”, things went back to normal.
It would take me another five years to fully understand why. For my new book, The Age Code, I have been investigating hidden vulnerabilities within our DNA which can influence how we respond to certain nutrients or diets which can alter the rate at which we age. It turns out that one of the best examples of this is caffeine.
I decided to have my DNA sequenced, by a Canadian company called Nutrigenomix, with the aim of finding out, among other things, the exact variant I carried of a gene called CYP1A2. This controls the behaviour of an enzyme which acts as one of the body’s primary detoxifiers, helping us break down compounds including caffeine.
In recent years, geneticists have discovered that when it comes to this gene, the population is split into two camps – half of us metabolise caffeine slowly, the other half can process it up to four times faster. If you’re in the former group, your body eliminates caffeine slowly and is more impacted by its stimulating effects.
My DNA test confirmed I’m a slow metaboliser – as suggested by the eyelash twitching. For me and my fellow slow metabolisers, a single cup of coffee is equivalent to drinking around three.
This is particularly important because in recent years research has highlighted that coffee consumption may play a significant role in health and ageing. For example, trigonelline, a plant chemical found in coffee, has been linked with helping to preserve muscle mass as we get older, while numerous other studies are increasingly showing that a daily dose of caffeine seems to help with slowing brain ageing.
“Caffeine definitely plays a role in inhibiting oxidative stress, something which damages cells in the brain and is one of the biggest features of Alzheimer’s disease and Parkinson’s,” says Ralph Martins, a professor of neurobiology at Macquarie University in Australia.
But the amount of caffeine you should be consuming, and whether it helps or hurts you, varies depending on whether you’re a fast or slow metaboliser. According to Sara Mahdavi, a clinician scientist and research fellow at the Harvard TH Chan School of Public Health, fast metabolisers can definitely benefit from three or four cups per day. But for slow metabolisers, it’s now thought to be better for your long-term health to stick to a single cup before switching to decaffeinated options, otherwise the overload of caffeine in your bloodstream can place excessive strain on your heart.
“Fast metabolisers can handle the caffeine and also really benefit from the other antioxidants within coffee,” says Mahdavi. “But slow metabolisers are much more vulnerable to the toxic effects of caffeine. It’s a vasoconstrictor, which means it causes the muscles around blood vessels to tighten, and when they have three cups of coffee, they’re vasoconstricting by multiple folds.”
Now, you probably don’t need to get a nutrigenetics test to figure out whether you’re a fast or slow caffeine metaboliser – you just need to listen to your body. While my eyelash twitching was a giveaway, other people can find themselves feeling particularly jittery, suffering from heart palpitations or struggling to concentrate after two cups of coffee. These are signs that they might be slow metabolisers. Since my own discovery, I now try to limit myself to a single cup per day before switching to decaffeinated or lower caffeine options such as tea.
But the role of nutrigenetics extends far beyond caffeine. DNA tests are set to play an important role in public health, by offering new information on how people metabolise nutrients. According to James Brown, founder of the nutrigenetics company Muhdo Health, people with certain variants of the genes FUT2 and TCN1 are more likely to struggle to absorb vitamin B12 through their guts.
Brown says this is particularly important information for anyone considering going on a plant-based diet as these people will be markedly more vulnerable to developing deficiencies, something which can affect cognitive health. “If you’ve got poor B12 metabolism from a genetic point of view, coupled with the fact now that you’re not having meat, you’re not having dairy or any of the sources that are really going to give you enough B12, then you’re going to go downhill quite quickly,” he says.
Likewise, around a fifth of the population are thought to have two copies of a particularly problematic variant of a gene called MTHFR, which influences our ability to clear an amino acid called homocysteine from the blood. Homocysteine is produced when we metabolise protein from food, and it’s a key building block which our body uses to construct and repair new tissues. But if you’re part of the unlucky 20 per cent and your body doesn’t clear it well, homocysteine can cause irreparable damage to your blood vessels.
Because many people are not aware that they carry this genetic variant, they’re unknowingly at a much greater risk of developing blood clots and premature cardiovascular disease. They could counter the effect by getting more vitamin B12 and folate in your diet, through consuming organ meats, cooked lentils and leafy green vegetables, or taking supplements.
“If you have the MTHFR mutation, and you’re not eating the right foods or taking a vitamin B12 supplement, your blood vessels will be ruined when you’re 50 years old,” says the geneticist Wei-Wu He, executive chairman of the Human Longevity organisation, and one of the founding scientists of the Human Genome Project.
Nutrigenetics can also reveal more about ourselves. As well as being a slow caffeine metaboliser, I discovered that I carry a variant of the FUT2 gene which means I need to make sure I keep consuming vitamin B12-rich foods or perhaps taking a supplement in years to come. But I also discovered that I’m a “supertaster” for fats – explaining why I’m particularly partial to deep-fried or greasy foods like fish and chips, and more prone to overeating if I allow myself too many of them.
In the future, geneticists believe that nutrigenetics can start to play a role in clinical decision-making, allowing doctors to make more accurate recommendations when it comes to certain nutrients that will particularly benefit an individual patient.
When I interviewed Professor Baukje de Roos at the University of Aberdeen, she explained that we know that consuming omega-3s in the form of fish oil is an effective way, on average, of lowering the levels of blood fats called triglycerides, a key risk factor for heart disease.
But the extent to which omega-3s are effective also depends on a variety of factors, ranging from a person’s gender to the amount of low-grade inflammation in their body, the profile of various fats in their blood, and their genetics. In future, de Roos hopes that it will become possible to screen people and develop an algorithm which would pinpoint the individuals who are most likely to see a significant boost to their cardiovascular health from taking omega-3s.
“That’s the ultimate goal,” she says. “Can we prescribe dietary interventions for people who we know will benefit from them?”
Having such granular data could even make it more feasible to persuade health insurers to cover the costs of dietary changes. “We know that healthy diets are more expensive, but can we get the insurance companies to consider the idea of, ‘Why do we always automatically pay for a drug when we know that in some groups, we could do a dietary intervention which is equally effective and doesn’t have the side effects that drugs do?’” she says. “So that could be the future, but we still need a lot more evidence to get there.”
The Age Code : The New Science of Food and How It Can Save Us by David Cox is published by Fourth Estate