10% Human: How Your Body’s Microbes Hold the Key to Health and Happiness. Alanna Collen

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СКАЧАТЬ of skin, you have two square metres of gut. Though it’s on the ‘inside’, the gut has just a single layer of cells between what’s essentially the outside world, and the blood. Immune surveillance along the intestines, therefore, is critical – every molecule and cell that passes by must be assessed and quarantined if necessary.

      Although the threat of infectious disease has all but gone, our immune systems are still under fire. But why? Let’s turn to the technique pioneered by Dr John Snow during Soho’s cholera outbreak of 1854: epidemiology. Since Snow first applied logic and evidence to unravelling the mystery of the source of cholera, epidemiology has become a mainstay of medical sleuthing. It couldn’t be simpler: we ask three questions: (1) Where are these diseases occurring? (2) Who are they affecting? and (3) When did they become a problem? The answers provide us with clues that can help us to answer the overall question: Why are twenty-first-century illnesses happening?

      The map of cholera cases that John Snow produced in answer to Where? gave away cholera’s likely epicentre – the Broad Street pump. Without much detective work, it’s clear to see that obesity, autism, allergies and autoimmunity all began in the Western world. Stig Bengmark, professor of surgery at University College London, puts the epicentre of obesity and its related diseases in the southern states of the US. ‘States like Alabama, Louisiana and Mississippi have the highest incidence of obesity and chronic diseases in the US and the world,’ he says. ‘These diseases spread, with a pattern similar to a tsunami, across the world; to the west to New Zealand and Australia, to the north to Canada, to the east to Western Europe and the Arab world and to the south, particularly Brazil.’

      Bengmark’s observation extends to the other twenty-first-century illnesses – allergies, autoimmune diseases, mental health conditions and so on – all of which have their origin in the West. Of course geography alone does not explain the rise; it merely gives clues as to other correlates, and with luck, the cause. The clearest correlate of this particular topography of illness is wealth. A great accumulation of evidence points to the correlation between chronic diseases and affluence, from grand-scale comparisons of the gross national product of entire countries, to contrasts between socio-economic groups living in the same local area.

      In 1990, the population of Germany provided an elegant natural experiment into the impact of prosperity on allergies. After four decades apart, East and West Germany were reunifying following the fall of the Berlin Wall the previous year. These two states had much in common; they shared a location, a climate, and populations composed of the same racial groups. But whilst those living in West Germany had prospered, eventually catching up and keeping pace with the economic developments of the Western world, East Germans had existed in a state of suspended animation since the Second World War and were significantly poorer than their West German neighbours. This difference in wealth was somehow related to a difference in health. A study by doctors at Munich University’s Children’s Hospital found that the richer West German children were twice as likely to have allergies, and three times as likely to suffer from hay fever.

      This is a pattern that repeats itself for many allergic and autoimmune conditions. American children living in poverty are historically less likely to suffer from food allergies and asthma than their wealthier counterparts. The children of ‘privileged’ families in Germany, as judged by their parents’ educations and professions, are significantly more likely to suffer from eczema than those from less privileged backgrounds. Children from impoverished homes in Northern Ireland are not as prone to developing type 1 diabetes. In Canada, inflammatory bowel disease more often accompanies a high salary than a low one. The studies go on and on, and the trends are far from local. Even a country’s gross national product can be used to predict the extent of twenty-first-century illnesses within its population.

      The rise of so-called Western illnesses is no longer limited to Western countries. With wealth comes chronic ill-health. As developing countries play economic catch-up, the diseases of civilisation spread. What began as a Western problem threatens to engulf the rest of the planet. Obesity tends to lead the way, and has affected large swathes of the population already, including those in developing countries. Its collective of associated conditions such as heart disease and type 2 diabetes (an insensitivity to insulin, rather than a lack of it) are trailing not far behind. Allergic disorders, including asthma and eczema, are also at the forefront of the spread, with rises under way across middle-income countries in South America, Eastern Europe and Asia. Autoimmune diseases and behavioural conditions appear to lag the most, but are now particularly common in the upper-middle-income countries, including Brazil and China. Just as many of our modern illnesses reach a plateau in the wealthiest countries, these conditions begin their ascent elsewhere.

      When it comes to twenty-first-century illnesses, money is dangerous. The size of your salary, the wealth of your neighbourhood and status of your country all contribute to your risk. But of course, simply being rich does not make you ill. Money may not buy happiness, but it does buy clean water, freedom from infectious disease, calorie-rich foods, an education, a job in an office, a small family, holidays to far-flung places, and many other luxuries besides. Asking Where? tells us not just the location of our modern plagues, but that it is money that’s bringing us chronic ill-health.

      Intriguingly though, this relationship between increasing wealth and poorer health disconnects at the very richest end of the scale. The wealthiest people in the wealthiest countries appear to be better able to lift themselves clear of the chronic disease epidemic. What begins as a preserve of the rich (think tobacco, takeaway food and ready meals) ends as the staple of the poor. Meanwhile, the well-off gain access to the latest health information, the best health care, and the freedom to make choices that keep them well. Now, while the richest cohorts of society in developing countries gain weight and acquire allergies, it is the poorest in developed countries who are more and more likely to be overweight and to suffer from chronic ill-health.

      Next, we must ask Who? Does wealth and a Western lifestyle bring ill-health to everyone, or are some groups affected more than others? It’s a pertinent question: in 1918, as many as 100 million people died from the flu pandemic that swept the globe after the First World War. Asking Who? provided an answer, that, with today’s medical knowledge, could potentially have considerably reduced the death toll. Whereas flu usually kills vulnerable members of society – the young, the old, and the already sick – the 1918 flu killed mainly healthy young adults. These victims, in the prime of their lives, are likely to have died not from the flu virus itself, but from the ‘cytokine storm’ unleashed by their immune systems in an attempt to clear the virus. The cytokines – immune messenger chemicals which ramp up the immune response – can inadvertently lead to a reaction that’s more dangerous than the infection itself. The younger and fitter the patients, the greater the storm their immune systems created, and the more likely they were to die from the flu. Asking Who? tells us something of what made this particular flu virus so dangerous, and would have enabled us to direct medical care not just at fighting the virus, but also towards calming the storm.

      Who? is composed of three elements. What age are those affected by twenty-first-century illnesses? Are there differences in how these conditions affect people of different races? And are the sexes affected equally?

      Let’s start with age. It’s easy to assume that diseases associated with developed, wealthy countries, where health care is good, are an inevitable consequence of our ageing population. Of course new diseases are on the rise! you might think. We live so long now! Surely so many of us living well into our seventies and eighties guarantees a whole host of new health challenges? Of course, as we release ourselves from the burden of death-by-pathogen, we will inevitably suffer from death-by-something-else, but many of the illnesses we face now are not simply diseases of old age, released by our longer life expectancy. Unlike cancer, whose rise is at least partly attributable to the cellular replacement process breaking down in older bodies, twenty-first-century illnesses are not all old-age-related. In fact, most of them show a preference for children and young adults, despite being relatively rare СКАЧАТЬ