The Miracle Pill
Page 5
These effects happen over time, but as we saw at the start of the chapter, movement has a more-or-less immediate impact on how the body functions. At the centre of this acute response to movement are lipoproteins, particles which transport various types of fat around your bloodstream, including cholesterol and less household-name fats like triglycerides.
In the broadest terms, while some blood-fats are seen as unproblematic, like high-density lipoprotein cholesterol (HDL), significant levels of another type of cholesterol, low-density lipoprotein (LDL), and of triglycerides spell trouble, and are linked to an increased risk of heart disease, not least via constricted arteries. It has been shown conclusively that activity shifts the balance of these substances away from the health-harming variants.
Many dozens of studies have proved this effect, some showing that even walking on a treadmill can help notably reduce lipaemia, the technical term for high fat concentrations in the blood.5 This effect is more significant in people who are otherwise fit, but still happens if you are not.
The other hugely significant function kickstarted by movement is the processing of sugars in our bloodstream, a vital ability in the prevention of type 2 diabetes and other metabolic disorders. Skeletal muscle plays a key role in this, and as we saw with Richard Mackenzie’s experiments, even a single bout of activity can improve the body’s response to insulin.
The role of movement in helping us deal with both fats and sugars is particularly important in the immediate aftermath of food, what is known officially as the postprandial state. There is, of course, one problem here. In the modern world, most people consume their largest single dose of high-fat, high-sugar foods in their evening meal. And then, rather than going out for a bracing stroll, they instead walk just a few paces to the sofa – if they’re not there already – and watch TV for a couple of hours. It’s no wonder our bodies eventually protest.
A body shut down
I ask Xand van Tulleken, the public health expert and TV doctor we heard from earlier, how he explains the health dangers of long-term inactivity to people in the most basic terms. He makes the parallel with space travel, and the well-documented impact on astronauts’ bodies of zero gravity and the ensuing lack of physical exertion, including weaker bones, wasted muscles, and even longer-term changes.
It is an intriguing parallel. As mentioned before, Van Tulleken is one of a pair of identical twins. Perhaps the most fascinating study on the health effects of space travel saw NASA compare the changes to Scott Kelly, an astronaut who spent six months on board the International Space Station, and his identical twin, Mark, who remained on Earth. As well as changes to muscle mass and bone density, the NASA scientists found Scott Kelly experienced narrowing of his arteries, while his brother did not. Perhaps most unexpectedly, the long space flight appeared to alter some of his genes, particularly those connected to the immune system, with not all the changes reversed when he returned to normal gravity.6
Another parallel van Tulleken uses is what happens to people left immobile in hospital. ‘If I put you in intensive care you will lose about 2–3 per cent of your muscle mass per day because you’re still,’ he explains. ‘And that’s what we’re all bloody doing at home now. What I try to explain to people is that when you don’t move your body it starts to just decay immediately. It’s very expensive for your body to maintain itself the way it is. And so as soon as there’s no stress put on your body, it’s like, “Well, fuck this, I’m just going to shut it all down.” Over time, what it will do is increase your risk of every single illness and it will make you die earlier, and along the way, your life will become much worse.’7
This might be a more vivid summary of the risks from inactivity than found in the official guidance, but the core message of both is the same. One of the most comprehensive government round-ups of the relevant science comes in the Physical Activity Guidelines Advisory Committee, or PACAG, a near-800-page report to the US government by a panel of the great and good of the physical activity world.8
First published in 2008 and updated ten years later, it stresses the ‘clear inverse dose–response relationship between the amount of moderate-to-vigorous physical activity and all-cause mortality’. In other words, if you don’t move about much, your chances of dying before your time are increased. The 2008 edition put this effect at about 30 per cent. The 2018 update dispensed with the specific figure, but added that ‘the strength of the evidence is very unlikely to be modified by more studies of these outcomes’. In other words: case closed.
There are many hundreds of individual studies purely on the risk of an earlier death from long-term inactivity, all reaching pretty much the same conclusion via slightly different routes. One mammoth piece of research which tracked the lives of more than 250,000 Americans aged fifty-plus found that those who reached the recommended minimum of 150 minutes a week of moderate activity had a 27 per cent lower chance of dying over the five-year research period than those who were inactive. If they managed at least some vigorous exertion, the figure rose to 32 per cent, and for people who managed both, it shot up to 50 per cent. Even engaging in some activity, but below the minimum, reduced the risks by 18 per cent.9
Another paper assessed the actual fitness of more than 13,000 men and women, as an objectively measurable proxy for movement. This found that after adjusting for all other factors, among men, those in the least fit 20 per cent of the cohort were more than three times more likely to die over the course of the study than the fittest 20 per cent. With women, the difference between the groups rose to four times.10
There are many dozens more such studies, and detailing any more runs the risk of both repetition and gloominess. But it’s worth explaining how this risk plays out on a global, population-wide level. One of the main studies in the edition of The Lancet devoted to physical inactivity, mentioned in the previous chapter, tried to undertake the most comprehensive reckoning yet of the global burden of illness and early death from inactivity. It was led by I-Min Lee, a professor of epidemiology at Harvard University, who is perhaps the world’s foremost modern expert on the connection between inactivity and ill-health. Her co-authors also comprised something of an all-star team from the discipline. They included several people whose names crop up elsewhere in the book, among them Steven Blair, who we also encountered in the last chapter, and Pukka Peska, a Finnish doctor who set up what is generally recognised as one of the most successful public health programmes in modern history. These were people who knew what they were talking about.
Their paper used complex formulae to crunch together the prevalence of inactive living around the world, and then the risks this creates, across nations, for a huge range of conditions including heart disease, high blood pressure, strokes, type 2 diabetes, various cancers, bone health, cognitive function and the risk of falls among older people. The headline conclusions were that, worldwide, inactivity is responsible for between 6 per cent and 10 per cent of all these conditions. This leads, the authors said, to around 9 per cent of deaths worldwide, making inactivity as deadly as the far more discussed issues of smoking and obesity.
Using 2008 as the base year for the data, the paper calculated that this meant 5.3 million fatalities due to inactivity, not far short of 15,000 people a day. The authors, however, noted that given the likelihood of even stronger associations between inactivity and disease than factored in the study, plus that much of the activity data was self-reported and thus likely to be exaggerated, ‘our estimates are likely to be very conservative’.11 Quite how conservative remains to be seen – Lee is currently leading an update of the study – but some epidemiologists privately say the real global death toll is likely to be closer to 7 million or 8 million a year.
It’s worth noting that a slightly earlier attempt to come up with an annual global death toll for inactivity, from the World Health Organization (WHO), reached a lower, if still alarming, total. The report from the WHO’s Global Burden of Disease team concluded that around 3.2 million deaths a y
ear could be attributed to inactivity, less than tobacco use but more than obesity.12 But in a follow-up article for The Lancet in 2013, Lee and some colleagues examined the discrepancy and argued that the WHO’s metrics for activity and the risks of mortality were ‘unclear’ – as close as a scientist ever gets to openly saying, ‘I think you’ll find that we were right.’13
When it comes to research into the individual diseases and conditions worsened by prolonged inactivity, the number of studies runs into the countless thousands. I’ll detail some of them in subsequent chapters, but as an introduction to the sheer scale of the health risks involved, here is a condensed list.
Cardiovascular diseases: The very first research connecting inactivity to poor health, published in 195314 and about which we’ll hear more in the next chapter, looked at the risk from heart attacks. Subsequent research has shown ever-stronger links between immobile living and not just heart-related deaths but conditions like high blood pressure and narrowed arteries. The benefits are all the more so if the activity is vigorous. One huge study found men who ran for an hour or more a week cut their risk of heart disease by 42 per cent, while those who walked briskly for thirty minutes or more a day saw an 18 per cent reduction.15 A review of the science in the 2018 PACAG report concluded there is ‘no lower limit’ for risk reduction – that is, even tiny amounts of movement will do good. This is true, it added, whatever your age, gender, weight or race.16
Cancer: Dozens of studies have suggested reaching at least minimum recommended activity levels can reduce the risk of colon cancer by 30–40 per cent in both men and women, while women see a reduction in breast cancer risks of around 20–30 per cent. The PACAG report, which devotes a full sixty-five pages to cancer, concludes that as well as these two there is also a strong relationship between activity and a lower risk of bladder cancer, renal cancer, oesophageal cancer, gastric cancer and endometrial cancer, as well as moderate evidence for lung cancer, and some, if limited, evidence connected to cancers of the blood, prostate, pancreas, ovaries, and head and neck.17
Precisely how activity limits these risks remains up for debate, and in part depends on the cancer. One possibility for breast cancer is that when women are active this can reduce concentrations of certain hormones linked to the condition. Another apparent link could be the effect of inactivity on mitochondria. Yet another theory draws links between inactive living and excess weight and inflammation, both of which are implicated with higher cancer risks.
Type 2 diabetes: This is a slightly more complex relationship, as the onset of the lifestyle-related version of the chronic metabolic condition is linked very closely to not just lack of movement but excess weight, as well as excessive time sitting down, with the various factors interconnecting. As a headline figure, studies have shown that a combination of greater activity and dietary interventions can cut the risk of type 2 diabetes in susceptible people by about 60 per cent, far greater than the benefit of any drug yet developed.18
Bone and joint health: A hugely significant and often neglected health issue. As we saw with the Neolithic hunter-gatherers earlier, bone mass is intimately connected to activity, with strength laid down in childhood and, if we are not careful, ebbing away in later decades. As an indication of the scale of the problem, in England alone, around 250,000 older people are hospitalised a year because of falls, with an estimated 9,000 dying.19
Cognitive function and dementia: This is one of the most fast-moving and exciting areas of activity science. Even senior academics who have seen it all in the physical movement world perk up when they talk about this, with good reason. A series of studies have shown regular activity can seemingly not just reduce your chance of developing Alzheimer’s or other forms of dementia, but can even reverse some of the memory-sapping effects of ageing. It appears to particularly improve so-called executive functions, those connected to higher-level cognition like planning and task management, with scans showing the relevant parts of the brain can actually increase in size.
Mental health: The idea of movement or exercise having mood-lifting effects, the much-touted ‘runners’ high’, is long-established, and popularly attributed to a rush of endorphins, the body’s natural opiates that are primarily there to dull pain. This is in some doubt, not least due to studies showing no apparent match between people’s reported mood and measured endorphin levels. Nonetheless, there is robust, repeated evidence that activity both reduces the risk of developing depression, and can help alleviate the symptoms of those who have it, with some studies suggesting a comparable effect to some drug regimes. There has been a similar effect demonstrated for anxiety, and even some studies showing staying active can assist with some of the symptoms of schizophrenia. Finally, there are numerous studies showing regular activity improves our sleep, both in terms of time and quality.
How much is enough?
There is, of course, an important if hopefully obvious caveat to all this: it is all about population-wide outcomes. It is possible for someone to spend their entire adult life never shifting more than a short trudge from an armchair while maintaining an enthusiastic intake of alcohol and tobacco, and still live to be 100. Similarly, someone else could be permanently active and scrupulously abstemious, and expire from a heart attack at forty. However, both would be statistical outliers. If you are inactive and sedentary, you are not necessarily going to become infirm or die younger than you would otherwise have done, or the converse for those whose life is filled with movement. But, all other factors being equal, the chances of this happening become notably greater.
So how much do you need to do to remain healthy? The first thing to look at is how activity and exertion are measured. There are two basic ways. To an extent, both are the domain of researchers and academics, those able to measure exertion levels and energy expenditure. But they are nonetheless hugely useful as a broad guide of what to aim for.
One metric, used mainly in population-level studies, is the physical activity level, or PAL. This is simply the amount of energy a person actually expends over a 24-hour period divided by their so-called basal metabolic rate (BMR) – that is, how much energy their body needs to just tick over in complete immobility. BMR depends on the individual. Men tend to have a higher level than women, due to larger amounts of muscle, while children’s rates are higher than those of adults as a proportion of their body size. The totals are nonetheless perhaps more than you might think, and can easily exceed 1,500 calories per day for an adult.
A PAL measuring anything from one to 1.4 is taken to mean someone is completely sedentary, even a hospital patient. Between 1.4 and 1.6 is inactive, for example someone with a desk job who doesn’t exercise outside work. From 1.6 to approaching two is deemed active, perhaps a person with a manual job, or a regular gym-goer. From two to 2.4 makes you very active – if your work isn’t physical it requires about two hours of exercise per day. And once you get beyond 2.4, you’re basically a professional sportsperson.
The other main measure is a gauge of exertion, called the MET, short for metabolic equivalent. One MET is simply the energy you are expending if you sit down and do nothing. This figure then multiplies according to how strenuous an activity is. This is where the value to a layperson comes in. While it depends on the age and fitness of the person performing the task, it’s possible to put broad MET figures to everyday activities. Thus, basic housework could be two METs, some light gardening more like three. Gentle cycling could take you five or six, while running tends to be twelve METs or above.
This is hugely useful to know, as one of the golden rules of the health benefits of activity is that it depends in part on the level of exertion. In the most basic terms, if light exertion does some good, the dividends really begin if it is moderate, and they multiply again if things become strenuous. In terms of METs, the general guide is that anything less than three METs is light, three to six is moderate, and above six is strenuous.
It is here that we enter the more practical world of guidelines. As we
saw in the last chapter, in the twenty-five or so years since governments started giving formal advice on the subject, for adults it has coalesced around the figure of 150 minutes of moderate activity a week. The WHO list of possible moderate activities20 includes brisk walking, gardening, DIY chores like painting, or playing games with children. Another option is to instead undertake at least seventy-five minutes of vigorous activity, for example reasonably quick cycling, running, labour-intensive gardening, or building work like digging a ditch.
With specific activities, there has been a lot of focus on walking, not least because it’s a straightforward thing that virtually everyone does. It is also one of the few areas of movement where a specific target seems to have fully permeated the public consciousness: the magic figure of 10,000 steps a day.
Before we delve into the curious history of that figure, it’s worth remembering that for walking to reach the WHO-mandated moderate exertion level, your pace must be ‘brisk’. This is often translated to mean about 3mph. However, humans don’t have built-in speedometers, and the actual speed will vary depending on factors like height, age and fitness. So what does it mean in more practical terms? I-Min Lee of Harvard University, who led the study into global deaths from inactivity, explains it thus: ‘I tend to put it that moderate walking is an intensity where, say, you think about meeting someone for lunch and you’re a little bit late so you walk at a pace so you get there in time. Or you can think of it as an intensity level where you can still talk but you can’t sing.’21
This area is the particular specialisation of Catrine Tudor-Locke, professor of public health at the University of Massachusetts, who is one of the world’s foremost experts on the issue of both counting steps and working out how rapid they should be. While she welcomes the way the 10,000-step target has caught on, Tudor-Locke’s work focuses increasingly on how to persuade people to walk at sufficient pace. She describes the physical effect of a brisk walk as ‘not necessarily sweaty but your heart rate is elevated’.22