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Lessons in Longevity This year, the number of pensioners in the UK exceeded the number of minors for the first time in histo

admin2013-02-05  4
问题                           Lessons in Longevity
    This year, the number of pensioners in the UK exceeded the number of minors for the first time in history. That’s remarkable in its own right, but the real "population explosion" has been among the oldest of the old — the centenarians (百岁老人). In fact, this is the fastest-growing demographic in much of the developed world. In the UK, their numbers have increased by a factor of 60 since the early 20th century. And their ranks are set to swell even further, thanks to the ageing baby-boomer generation: by 2030 there will be about a million worldwide.
    These trends raise social, ethical and economic dilemmas. Are medical advances artificially prolonging life with little regard for the quality of that life? Old age brings an increased risk of chronic disease, disability and dementia, and if growing numbers of elderly people become dependent on state or familial support, society faces skyrocketing costs and commitments. This is the dark cloud outside the silver lining of increasing longevity. Yet researchers who study the oldest old have made a surprising discovery that presents a less bleak vision of the future than many anticipate.
    It is becoming clear that people who break through the 90-plus barrier represent a physical elite, markedly different from the elderly who typically die younger than them. Far from gaining a longer burden of disability, their extra years are often healthy ones. They have a remarkable ability to live through, delay or entirely escape a host of diseases that kill off most of their peers. Super-centenarians — people aged 110 or over — are even better examples of ageing gracefully. The average super-centenarian had freely gone about their daily life until the age of 105 or so, some 5 to 10 years longer even than centenarians, who are themselves the physical equivalent of people 8 to 10 years their junior. This isn’t just good news for the oldest old and for society in general; it also provides clues about how more of us might achieve a long and healthy old age.
    One of the most comprehensive studies comes from Denmark. In 1998, Kaare Christensen at the University of Southern Denmark, in Odense, exploited the country’s exemplary registries to contact every single one of the 3,600 people born in 1905 who was still alive. Assessing their health over the subsequent decade, he found that the proportion of people who managed to remain independent throughout was constantly around one-third of the total: each individual risked becoming more infirm, but the unhealthiest ones passed away at earlier ages, leaving the strongest behind. In 2005, only 166 of the people in Christensen’s sample were alive, but one-third of those were still entirely self-sufficient. This is good news from both personal and societal perspectives, for it means that exceptional longevity does not necessarily lead to exceptional levels of disability.
Of course, people can live independently without being entirely healthy, and it is true that most centenarians suffer from some sort of ailment. These range from osteoarthritis which is almost universal and often omitted from studies — to simple loneliness.
    Neurodegenerative (神经退化性) diseases are common too, with around 70 to 85 per cent of centenarians suffering from some form of dementia. But dementia in this group follows a different pattern to the general population. It is more likely to be vascular dementia or rare neurodegenerative conditions, such as Pick’s disease or Lewy body disease.
    Alzheimer’s disease, the most common form of dementia, is relatively rare among centenarians yet, intriguingly; autopsies reveal that the brains of the oldest old, who had shown no outward sign of dementia, are sometimes riddled with the lesions associated with Alzheimer’s disease. The basis of this resilience to Alzheimer’s is largely unknown. The simple fact is that many people who become centenarians seem able to tolerate damage that would significantly harm less robust individuals, and although many suffer from dementia as death draws near, most remain mentally agile well into their nineties. Not all of the oldest old survive by delaying illness or disability, though — many soldier through it. Jessica Evert of Ohio State University in Columbus examined the medical histories of over 400 centenarians. She found that those who achieve extreme longevity tend to fall into three categories. About 40 per cent were "delayers", who avoided chronic diseases until after the age of 80. This "compression of morbidity", where chronic illness and disability are squeezed into ever-shorter periods at the end of life, is a recent trend among ageing populations. Another 40 per cent were "survivors", who suffered from chronic diseases before the age of 80 but lived longer to tell the tale. The final 20 per cent were "escapers", who hit their century with no sign of the most common chronic diseases, including heart disease, cancer, diabetes, hypertension and stroke. Intriguingly, one-third of male centenarians were in this category, compared with only 15 per cent of women.
    So what are the secrets of a long and healthy life? Gerontologists (老年医学家) point to four key factors: diet, exercise, "psycho-spiritual" and social, so anyone aiming for a century should not underestimate the power of lifestyle — despite the odd centenarian who proudly claims to have smoked 60 cigarettes a day for decades. Thomas Perls, who heads the NECS, believes that up to 70 per cent of longevity is due to non-genetic factors. Nevertheless, many people who live well into old age do tend to have another advantage: an inherited genetic pass.
    Take a close relative of a centenarian and you can put good money on their chances of living a long life. Among Americans born in 1900, brothers of centenarians were 17 times as likely to reach a century as their peers, and sisters, eight times. The New England study reveals that the children of centenarians are less than one-third as likely to die of cancer as the general population, and less than one sixth as likely to die of heart disease.
    Further evidence of a genetic link comes from longevity hotspots. Okinawa in Japan is the front runner. At 58 centenarians per 100,000 people, it has the world’s highest proportion in this age group — more than five times the level of some developed countries. Like other hotspots, including Sardinia and Iceland, Okinawa is a relatively isolated island community, which leads to higher levels of inbreeding and a clustering of genetic variants. While such genetic similarity usually has detrimental effects, in these hotspots it seems to have united and maintained genetic variants that predispose people to a long life.
    Of course, members of isolated communities or families usually share a particular environment too, but this alone cannot explain clusters of longevity. Gerontologists have found that the influence of environmental factors such as wealth or education on lifespan fades as we age, while that of genes increases. By comparing 10,000 pairs of Scandinavian twins, Christensen found that genes only start exerting a strong influence on our lifespan after the age of 60. Before then, both identical and non-identical twins have largely independent odds of reaching a given age. Beyond 60, however, the odds of one twin reaching a given age are greatly increased if their cotwin has done so, especially if the twins are identical.
    This makes the "centenarian genome" a key resource for identifying "longevity genes", an invaluable step in understanding the physiological processes underlying long lives.
    Such genes have been found in abundance in other organisms — including over 70 in the worm Caenorhabditis elegans (秀丽线虫). Unfortunately, it’s a different story in humans. While many candidate genes have been suggested to affect lifespan, very few have been consistently verified in multiple populations.
    So far the search for longevity genes in humans has been extremely difficult, but prospects brighten as genomic technologies become faster and there are more centenarians to study. Only a lucky few win the genetic lottery of longevity, but if we understand what sets them apart, we may be able to make the rest of us more like them by using lifestyle or therapeutic interventions to manipulate physiological pathways. Such medical advances will not only extend our lives, but also help us remain healthy and independent for as long as possible.
Besides the number of available centenarians, the advancement of______will make it possible to find longevity genes in humans.
选项
答案genomic technologies
解析 该句提到，到目前为止，人类身上的长寿基因还没有被发现，但是前景是光明的，因为基因技术(genomic technologies)的发展十分迅速，并且也有更多的百岁老人可以研究。题干中已经给出了the number of available centenarians，所以答案出处在genomic technologies become faster。题干中的the advancement of对应become faster，由此可知答案为genomic technologies。
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