“西雅图纵向研究”(Seattle Longitudinal Study)从1956年开始追踪6,000人的心智能力。这是迄今为止同类研究中历时最长的一项：所有的志愿者每过7年都会接受一次测试。虽然年龄较老的志愿者不太擅长数学，而且对命令的反应速度也会减慢，但他们在四五十岁时的词汇、空间、方向、言语记忆和问题解决能力却好于二十多岁时。
“Growing old is great – when you consider the alternative,” as the saying goes.
Welcome to the age of ageing. With more than 800 million people over 60 and more centenarians than the population of Iceland (that’s about 329,000), the world is having to brace itself for the economic – and social – consequences. From a deluge of diseases to sagging skin and the dulling of the senses, old age is beset with creeping failures, medical interventions, and low expectations. But can there be a silver lining for those joining the grey brigade?
Growing old has been synonymous with bodily decay since ancient times. The Greeks had a particularly dire view – many saw ageing itself as a disease. Yet the latest scientific research suggests ageing isn’t a straightforward decline after all. As BBC Future has reported before, life peaks later than you might think.
When does old age begin?
The poet Dante believed old age started at 45. A survey of the British public concluded that it starts at 59 – the older the respondent, the greater the number of years they considered old. But the United Nations and most scientists define it as any age after 60.
It’s not just the brain that gets wiser with age. The human immune system encounters millions of potential dangers every day. As the body’s police force, it needs to learn to spot the dangers. For this, we produce unique white blood cells which are tailored to the molecular appearances of millions of different invaders. When they recognise a foe they stick around, forming an ‘immune memory’. The next time it turns up, they help to rally a rapid response.
John Upham from the University of Queensland says this memory can last a long time. “People who have gone through various epidemics, their immune systems can remember the virus for 40 or 50 years in some cases. It does begin to drop off in your 70s or 80s, but there’s a bit of a sweet spot for people – particularly from your 40s through to your late 60s and early 70s – where the immune system remembers the viruses experienced over the years.”
This cumulative protection translates into fewer colds. While 20-year olds can expect to catch two or three in a year, over 50s average only one or two.
Other immune defences however, tend to weaken with age. The body produces fewer new white blood cells, and they become sluggish. Aged immune systems also produce less antibodies – proteins which stick to pathogens to help identify and eliminate them. But what if this could be life-saving?
The 1918 flu pandemic was the deadliest in human history, killing 50 million people. But it was most lethal for those usually thought of as fit and strong, aged from 20 to 40. The 2009 swine flu outbreak followed the same bizarre pattern, with most fatalities in those under the age of 65.
It’s thought that the viruses caused their victims’ immune systems to overreact. Those with the most vigorous immune systems launched the most dramatic, and damaging, responses, in what’s known as a ‘cytokine storm’. A healthy immune response relies on positive feedback – when a pathogen is found, the surrounding tissues release chemical messages, called cytokines, asking for help. As cells arrive on site, they are encouraged to release the chemicals too, encouraging even more cells to arrive. But sometimes the loop gets out of control, killing healthy cells and leading to potentially fatal inflammation. It’s not yet known what triggers the storms, but ongoing research has inspired a new treatment for the flu which acts on the cytokine storm instead of the virus itself.
And there’s good news for those with allergies, too. While the ultimate causes of allergies are still hotly debated, all are mediated by antibodies. The main culprit is Immunoglobulin E and like all other antibodies, its production diminishes with age.
Mitchell Grayson from the Children’s Hospital of Wisconsin says the older you get, the less severe the symptoms are likely to be. “Allergic disease peaks in childhood and then seems to decrease throughout late adolescence and into their 20s. In the 30s there is another resurgence until people get into their 50s and 60s when the symptoms tend to get less common.”
There’s no shortage of slang terms to describe the destructive effects of ageing on the brain. Yet in a number of vitally important abilities, older brains actually turn out to be smarter.
Michael Ramscar from Tubingen University says we have misunderstood how the brain ages. “The number of neurons in the human brain peaks at around 28 weeks after birth, but as many as half of the neurons produced die by the end of adolescence. Since we don’t usually think of the period from birth to age 18 as one of hideous decline, it seems safe to conclude that brain size as measured in neuronal numbers is not much of an indicator of anything.”
The Seattle Longitudinal Study has followed the mental abilities of 6,000 people since 1956. It’s the longest-running study of its kind, with the same volunteers tested every seven years. While older volunteers aren’t as good at maths and are slower to respond to commands, for vocabulary, spatial orientation, verbal memory, and problem solving abilities, they were better in their late 40s and 50s than they were in their 20s.
Several studies have shown that older people have more – and better – sex than you might think
Gary Small, who studies geriatric psychiatry at the University of California Brain Research Institute, says it’s down to the knowledge accumulated thanks to all those extra years. “People develop a greater perspective of what’s important, the ability to problem-solve is streamlined after years of practice. And there’s accumulation of certain types of knowledge – what’s called crystallised intelligence.”
It’s a pattern underpinned by biology. Nerve signals are insulated by a fatty material, myelin, which envelops the wiry ends of neurons. It’s important stuff, increasing the speed electrical signals are transmitted, but it was thought to deteriorate as people got older. Not so. “As people age you find that the insulation around these long wires is actually increased, so axons fire more quickly in middle-aged people than in younger people. There’s a peak performance of these brain cells around that time,” Small says.
Several studies have shown that older people have more – and better – sex than you might think. A study of the sexual activity and satisfaction of women in their 80s found that half still had orgasms ‘always’ or ‘most of the time’ during sex. Other studies have reached similarly striking conclusions – a survey of people over the age of 60 found that 74% of men and 70% of women reported a greater sexual satisfactionthan when they were in their 40s. Tara Saglio, a relationship therapist based in London, puts this down to older women having fewer insecurities. “Older women are more confident about expressing their own sexuality. It’s that confidence that makes sex better.”
Migraines can become less of a headache as we age, too. ASwedish study of patients 18 and older found that attacks become shorter, less painful and less frequent as people get older. Of 374 people enrolled in the study, only four developed chronic headaches.
Sweat glands shrink and become less numerous as people get older. Research shows that those in their 20s can expect to sweat more than those on their 50s and early 60s.
Still not convinced? Even at advanced years, the Grim Reaper need not be as close as you might expect. The oldest old are healthier than ever before and still have a good chance of celebrating a few more birthdays. In 2011-2014, the average 25-year-old had a life expectancy of 84 (women) or 80 (men), while a 95 year-old could expect to see their 98th (women) or 97th (men) birthday. Even at 80, women have a 95% chance of living another year.