Here is the bad news. As we age our bodies change: our skin becomes less elastic, our hair thins, we lose as much as two inches in height by the time we are 80, we lose muscle mass, and some of the mineral content in our bones. Our senses become less acute: most of us need glasses by the time we are in our 40s, and it becomes more difficult to hear the high-frequency sounds of human speech. We sleep less long and not as deeply. Our metabolism slows and we need less food. Our brains become smaller with less blood flowing through them; some memory loss is normal. Our organs also change: most of them become less efficient and more vulnerable to extremes of activity or diet. Male sexual response times slow and women stop ovulating. The pace of aging varies not only because of differences in one’s genetic makeup but also because of income, social status, education and many other determinants of health. Heart problems, arthritis, lung disease, chronic digestive issues and their associated problems are much more common as we age. Dealing with such conditions is a significant part of the normal aging process.
There are many ways in which the health status of humans has changed over the centuries. For example, we know that for many centuries life expectancy at birth was between 30 and 35. There was a very high rate of infant and child mortality. Many deaths were due to infectious diseases – typhoid fever, cholera, small pox among others. In fact, if you lived to the age of 20 your chances of surviving to 60 were pretty good.
The critical point for me is that in previous eras almost everyone over the age of 40 had one or more chronic diseases. For example, while doing some work on seventeenth century philosophy and science, I found that many of the famous philosophers and scientists of the time, such as John Locke, Robert Boyle and Thomas Hobbes, all suffered from chronic diseases from quite early on. Many of these conditions were the consequence of infectious diseases that they had survived as children or teenagers. By the time they were 40, they and their peers were considered to have entered old age. Still death was not usually a result of chronic conditions – at all ages the greatest risk of dying was from the big killers, like cholera, tuberculosis, and other infectious diseases.
A great shift in mortality began in the industrialized world in the middle of the nineteenth century. Longevity was increasing and many of the diseases of aging were starting later in life. Today, we hear that “60 is the new 40.” And it is. This rapid increase in life expectancy is continuing, as is the delay in the onset of age related morbidity. One can describe the changes of the last several centuries in terms of this delay of the onset of the diseases associated with aging. If in the 1600s almost everyone over 40 had one or more chronic diseases, now almost everyone over 65 is affected. If old age began at 40 in the 1600s, we can say that it now begins at 65.
Some of the main features of the mortality shift are the reduction of maternal and infant mortality, and the elimination of many communicable diseases. Infant mortality in the developed world has dropped by almost a hundredfold from more than 10% to almost 0.1% over the last 150 years. Maternal mortality which was about 500 for every 100,000 births is now about 12. Deaths from diseases like small pox, cholera, typhoid fever tuberculosis and other communicable diseases have virtually disappeared in Canada and other developed countries. The recent WHO atlas of morbidity tells us that in Canada 89% of deaths are due to non-communicable chronic diseases. Competing explanations of the Mortality Shift have greatly impacted health policy, some of which I will review in the next blog.