Is your heart a ticking time bomb?

There are many reasons running gives us a feel-good glow. There’s the endorphin rush, the stress relief, the sense of accomplishment and the knowledge we’re doing ourselves good. Countless studies, encompassing vast numbers of subjects – young and old, healthy and unhealthy (including heart attack survivors), slim and overweight – have affirmed the link between aerobic exercise and cardiovascular health. It’s estimated that hitting the recommended activity guidelines (150 minutes of moderate exercise, 75 minutes of vigorous exercise – or a combination of both – per week) slashes the risk of cardiovascular disease in half. If you’re a regular runner, you’re almost certainly ticking this box. Chances are, you’re doing more, which means even greater benefits, right? Well, that depends on who you ask…

American cardiologist Dr James O’Keefe is a leading proponent of the ‘too much exercise’ hypothesis, which argues, in his words, that, ‘a safe upper-dose limit potentially exists beyond which the adverse effects may outweigh its benefits.’ His TED Talk ‘Run for your life: at a comfortable pace and not too far’ has received over 400,000 views.

Last year, O’Keefe co-authored a paper in the Journal of the American College of Cardiology with Dr Peter Schnohr, a Danish cardiologist who set up the Copenhagen City Heart Study in 1976 to study risk factors for cardiovascular disease. Their paper argued that running fast, a lot, is as bad in terms of mortality rates, as not running at all. They advised a limit of no more than three sessions a week, not exceeding 2.4 hours in total, and at a slow-to-average pace (10-12min/mile). Cue shock headlines such as ‘Fast running is as deadly as sitting on the couch’ (Daily Telegraph) and ‘Too much jogging is just as bad as doing none at all’ (Daily Mail).

Too much of a good thing?

Six months later, Sam Lloyd, a healthy, fit 44-year-old runner from Kent with a love of long distances and an enthusiasm that has led her to coach four running sessions a week on top of her own training, collapsed after suffering a cardiac event. She had a pacemaker fitted and is now back running. But the episode has left her spooked – and confused. One doctor told her that running was to blame, while another ruled this out. ‘I don’t know how far I can push myself safely,’ she says. ‘I have questions that just haven’t been answered.’

O’Keefe and Schnohr’s study was subsequently heavily criticised for the way it presented and interpreted its data. The number of deaths among the 36 runners who did more than four hours running per week? Two. Critics argue such figures are too small to be statistically signifi cant. What’s more, we don’t even know how those two runners died – it may have had nothing to do with running. When you look at the data broken down by speed, the case for slowing down does not convince: there were six deaths among 201 runners who’d classified their typical running speed as fast (8 min/ mile), compared with seven of the 176 classified as slow (12 min/mile).

Nevertheless, the ‘too much of a good thing?’ debate has been hotting up, with the focus shifting towards insidious damage over years of training, rather than the traditional concern over sudden cardiac death. Two new reviews have been published this year, one titled ‘The potential cardiotoxic effects of exercise.’ Should we be concerned?

‘Let me start by saying there is no doubt in my mind that exercise is good for you,’ says Professor Sanjay Sharma, a consultant cardiologist at St George’s, University of London, and Medical Director of the London Marathon. ‘People who exercise have a better lipid profile, better blood pressure, they’re less likely to suffer diabetes or be obese and they live three to seven years longer than non-exercisers. If you could package up all the benefits of exercise it would be a miracle pill.’

But, says Sharma, these benefits arise from exercise meeting the current guidelines. ‘What about people who are doing 10 or 20 times this amount? Can too much of a good thing become a bad thing? At present, there’s a great deal of evidence that exercise is good for the heart and only a small amount of evidence that, for some people, there may be such a thing as too much.’

He cites a study in the Journal of the American Medical Association last year, which concluded that doing the recommended weekly 2.5 hours of physical activity brings a 30 per cent risk reduction in all-cause mortality. But do three to five times that amount and the risk reduces further, to 35 per cent. ‘They found you could do 10 times as much without increased mortality risk,’ says Sharma.

However, Schnohr, O’Keefe and others have talked about a ‘U-shaped curve’ in terms of endurance training’s effect on cardiovascular risk: the notion that the greatest risk reduction comes from the middle ground and that there is a point beyond which benefits are no longer accrued and exercise may become detrimental.

‘Almost everything in nature operates on some degree of U-shaped curve,’ concedes Dr Larry Creswell, a heart surgeon at the University of Mississippi’s School of Medicine, who writes a blog called Athlete’s Heart. ‘There’s a sweet spot and a point where there are diminishing returns and then, perhaps, harm. But in my opinion, that curve is not yet defined for athletes who do a lot of exercise. And there’s no reason to believe the same U-curve would apply to all.’

Sharma agrees with Creswell that the relationship between exercise volume and benefits is not linear. ‘You reap more benefits up to a point, and then you plateau,’ he says. ‘At some further point it becomes harmful. But that point is not going to be the same for everyone.’

There is no debate about the fact that long-term endurance exercise causes structural, functional and electrical changes to the heart. These changes, which include lower resting heart rate, thickening of the ventricle walls and increased heart chamber size, are collectively referred to as ‘Athlete’s Heart’ and generally considered benign, but some researchers have questioned this assumption. ‘These adaptations may also have deleterious effects,’ states a study review published recently in Physiological Reviews. ‘Cardiac biomarkers are acutely increased by exercise, and atrial fibrillation, myocardial fibrosis and coronary artery calcification appear more common in older athletes compared with their inactive peers.’

Disturbing stuff, but let’s look more closely at the research.

In the long run

Imagine you had your heart scanned just after a marathon or ultra: ‘It’s likely there’d be signs of damage,’ says professor Greg Whyte OBE, director of performance at the Centre for Health and Human Performance in London and the man who helped Eddie Izzard prepare for his epic marathon challenges. ‘We’d see raised cardiac troponins [associated with heart disease] in the blood – a clear sign of damage. In other circumstances, the presence of cardiac troponins is used to determine a heart attack, but following endurance exercise the rise is small, it happens in just about everyone and it rapidly returns to normal.’

This quick symptom reversal suggests there’s nothing to worry about – that any damage is merely transient. But not everyone is convinced. ‘Cytokines can paralyse and damage heart cells temporarily, but repeated over a number of years, a buildup of these microtraumas can result in healthy tissue being replaced by scar tissue,’ says Lars Andrews, a cardiac physiologist and founder of Cardiac Athletes, an online community for athletes with heart issues. In a study in which rats were made to exercise to extremes, they developed enlargement of all four chambers of the heart, abnormal heart stiffness, an increase in scarring and an enhanced susceptibility to dangerous heart rhythm problems that did not go away. ‘We can’t replicate such a study in humans,’ notes Sharma. ‘But studies of lifelong veteran athletes suggest there may be similar adverse cardiac remodelling.’

A study in which Sharma and Whyte were involved found that along with marked structural changes to the heart, 50 per cent of lifelong runners had myocardial fibrosis or heart-tissue scarring. While it was a very small study – just 12 runners – the incidence was correlated to the number of marathons and ultras they’d amassed and the number of years they’d been competing.

Another study, published in the European Heart Journal, looked at the heart records of more than 50,000 people who’d participated in extreme endurance races over a 10-year period. Researchers found that the more times subjects had raced, and the faster their finish times, the more likely they were to be hospitalised in the ensuing 10 years for an abnormal heart rhythm (arrhythmia).

‘Long-term endurance training does seem to do something to the heart,’ says Sharma. ‘In some instances, it can promote scarring and lead to more arrhythmias, including atrial fibrillation. It may be that some people’s genetics make their hearts more vulnerable to these issues, while others are protected. More quality research is needed. What we cannot do is rely on underpowered or scaremongering studies that may lead us to erroneous conclusions.’

Breaking our rhythm

Atrial fibrillation (AF) has featured prominently in the recent debate. A disturbance of the heart’s rhythm that produces an irregular and often rapid heartbeat, ‘AF is typically a disease of older people,’ says Sharma. ‘There’s a prevalence of around 10 per cent in the eighth decade and the condition is associated with a fivefold increased risk of stroke.’

However, a number of studies have highlighted an unexpectedly high incidence of AF among endurance athletes. One study, which compared the cardiovascular health of orienteers versus healthy controls, found that of 228 subjects with no risk factors for AF, 12 developed it. In the control group, just two of the 212 subjects free of risk factors developed AF, both of whom engaged in vigorous exercise. However, the study authors noted that most of the orienteers who developed AF responded well to medication and had continued competing.

Interestingly there may be a gender divide here, too: a review published in March this year concluded from existing data that a high volume of exercise raised the risk of atrial fibrillation among men (especially those under 50), but actually reduced it in women.

Richard Smith* is a runner and doctor who began suffering from AF five years ago, aged 49. ‘The first time it happened I was lying in bed,’ he says. ‘It felt as if the usual rhythmic beat in my chest had been replaced by a rabbit leaping around in a sack. My pulse felt weak and thready. I was shocked.’ That first episode lasted a few hours. In the years since, Smith has suffered a further 40 episodes, lasting from 15 minutes to 18 hours.

‘The research suggests there is a link between lifelong exercise and AF,’ says Sharma. ‘But it may be that the type of AF athletes get is somehow different. It’s almost unheard of for athletes with AF to have strokes, despite stroke being one of the major health risks associated with the condition. Perhaps the absence of other risk factors for stroke, as a result of regular exercise, protects them.’

It’s a point worth noting. Regardless of the number of endurance athletes – from marathon runners to Tour de France riders – found to have structural or electrical changes to the heart, the fact is that, as a group, they tend to live longer and suffer fewer diseases, including heart disease, than non-exercisers. ‘In terms of quality of life and length of life, exercise is beneficial,’ says Whyte.

Smith continues to feel well, running a thousand miles a year and playing football twice a week. ‘I’ve been checked out by a cardiologist and there’s no evidence of cardiomyopathy or ischaemic heart disease, meaning I have what’s known as ‘lone’ AF [where the condition is present without other risk factors],’ he says. ‘I’ve been told there is no need to cease physical activity.’ But he urges anyone experiencing arrhythmia to go for tests. ‘It’s important to exclude other risk factors and causes,’ he says. ‘And there have been significant advances in treating AF. A procedure called ablation, which kills the cells that cause the abnormal electrical activity, is rapidly becoming the treatment of choice.’

Tune in, check out

Getting yourself checked out isn’t always as easy as it should be, however. Doctors (especially those outside the field of cardiology) don’t expect healthy, active people to have heart problems, which is perhaps why it took so long for Sam Lloyd’s condition to be diagnosed.

‘My doctor never dreamt there was something wrong with my heart when I approached her,’ she says. The first indication of a problem came in the form of breathlessness. ‘I’d sometimes feel as if I had to gasp for air and I occasionally get dizzy. And training felt harder. I went to the doctor and had some blood tests.’ The results came back clear, but the breathlessness continued. Lloyd returned to her GP for a resting ECG (electrocardiogram), asthma check and lung X-ray. All these tests came back clear. Even an echocardiogram, a scan of the heart, found nothing untoward. But the symptoms continued, and Lloyd insisted there was something wrong. ‘I was told it was probably stress,’ she says. Finally, she was given a 24-hour ECG. ‘I was about to start my taper for a race in the Pyrenees,’ she remembers. A week later she received a call. ‘“Stop everything,” the doctor said. “Don’t be on your own and don’t do anything strenuous.” It was very, very scary.’

Lloyd’s heart was experiencing electrical malfunction – the ECG had revealed it was dropping to as low as 18 beats per minute and missing as many as six beats at a time. She was referred to have a pacemaker fitted but a few days later she woke up feeling unwell and asked her husband to take her to hospital, where she passed out. ‘I had a 20-second heart stop. They fi tted the pacemaker immediately.’ Lloyd has what’s known as first-degree heart block, in which the electrical rhythm of the heart is disrupted, and sinus bradycardia, where the heart rhythm slows. The pacemaker prevents her heart rate dropping too low, and steps in if it skips a beat. She now trains with a heart-rate monitor and backs off if she’s not feeling well.

‘Running puts us in tune with our bodies,’ she says. It was most likely that sense of awareness, built up over many years of running, that convinced her something was wrong and made her persist in looking into the cause. It underlines the importance of listening to your body and heeding warning signs, which can include the following:

  • Heaviness in the chest, chest pain or discomfort

  • Disproportionate shortness of breath

  • Unaccustomed fatigue

  • Blacking out (or nearly doing so)

  • Palpitations and arrhythmia

  • Giddiness and lightheadedness during exercise

Take heart

There are also sensible steps you can take to look after your heart. Lifestyle factors, such as not smoking, keeping stress under control and eating healthily are a given. But Andrews stresses the importance of avoiding training when you’re not 100 per cent healthy, particularly in the case of fever, which can lead to myocarditis, an inflammation of the heart that has been linked to subsequent scarring. He also flags up the importance of hydration to avoid putting undue stress on the heart through dehydration or overheating.

For Whyte, it’s about preparation. ‘People taking on big endurance challenges need to train correctly,’ he says. ‘What we’re seeing now with the emergence of these extreme challenges is an increasingly older field. In younger athletes, nearly all cardiac deaths are due to inherited heart problems. In the over 35s it’s mostly as result of acquired cardiovascular disease. You’ve got to have a look under the bonnet and exclude problems in the first place.’

It’s worth noting that despite the explosion in popularity of long-distance races, we haven’t seen a concomitant increase in deaths among runners and other endurance athletes, aside from the occasional rare, tragic case of undiagnosed cardiovascular disease. Whyte offers two reasons for this, both of which lead him to conclude that ultimately, we have little to worry about.

‘Firstly, the heart’s ability to cope is amazing,’ he says. ‘Lots of systems in the body are more likely than the heart to succumb to failure as a result of excessive exercise. And secondly, people prepare for these challenges properly – or if they don’t they get found out and have to quit before the damage is done.’

So where does all this leave us dedicated runners? Should you be ditching that autumn ultra? ‘I don’t think for one second that endurance running necessarily raises the risk of heart problems,’ says Sharma. In 35 years of the London Marathon, he says, there have been 14 deaths, not all of which were attributable to heart issues. And that’s despite the fact that in the last 30 years, the number of people running marathons has rocketed. Research has shown that the risk of dying from cardiac arrest in a marathon is one in 100,000, compared with an estimated rate among the general population of one in 1,000.

‘Of course there is a point where exercise gives diminishing returns and there may be a point where it begins to do more harm than good,’ says Creswell. ‘At present we don’t know where that point is and it’s unlikely to be at the same place for everyone. In the meantime, the overwhelming evidence is that exercise is good for you – even if you are exceeding the 150 minutes per week recommended for health.’

So, be sensible. Look after your heath holistically and don’t assume that running renders you immune from cardiovascular issues. But above all, keep in mind the fact – acknowledged by every single study mentioned here – that the many and varied benefits of exercise far, far outweigh the potential risks.


Photography by Dan Saelinger/Getty Images