AGING

The western lifestyle has brought heart disease, diabetes and obesity but it has also brought a remarkable increase in the number of years we live. In the past hundred years, the average lifespan in the US has increased from forty-nine to seventy-six years. We do not know why. Simple explanations like better food, better hygiene, better medical care, leave unexplained why people in Japan live longer than people in the US, or why, within the US, there is such a wide variation in lifespan.

Early pointers to the importance of the first few years of life in determining lifespan were calculations showing that, within western countries, each generation has lower death rates than the previous one at every age from birth to old age. It is as though from its earliest beginnings the vitality of each succeeding generation is enhanced beyond that of the generation that precedes it. Not only do a greater proportion of people attain eighty, ninety, even a hundred years of age but they reach these ages in better health: they are fitter and more mentally active than ever before. At any given age they are biologically younger than previous generations. 75 years of age today is biologically the same as 65 years in the past. Within western countries, the places where people have the longest life expectancy are the places where people are not only healthier but are biologically younger. In Scotland old people in Edinburgh, the wealthy capital city, are four years biologically younger than people of the same age in nearby Glasgow, a historically poor city of slums and shipyards.

different paths of early growth and development make people more or less vulnerable to agingAging is inevitable, but the rate at which we age is determined by the conditions of our lives. The realisation that different paths of early growth and development make people more or less vulnerable to aging processes is new; and at this time we only see the picture in outline. It is clear, however, that low birthweight in a baby born at term is a simple and available marker of a path of development that is sub-optimal and makes a person vulnerable to the stresses of later life. There are two different challenges in middle and old age. One is to slow the rate of biological aging: the other is to prevent age-related diseases, importantly heart disease, diabetes and osteoporosis. The two challenges are linked but the second is not an inevitable consequence of the first.

People differ in their inner environments, in the settings within their bodies by which they maintain an internal constancy. Some people need more sleep than others. Some people react more calmly to the ups and downs of life than others. These internal ‘homeostatic’ settings are established through our experiences as a baby and young child. Once established, internal constancy has to be maintained in the face of assaults from the outside world, and failure to maintain constancy leads to disease – high blood pressure, high blood sugar, thin bones. People who had low birthweight have more fragile ‘homeostatic’ settings that are more readily perturbed by the outside world. Older people who weighed 5, 6 or 7 pounds at birth may need protection from harmful influences that are of lesser or even no consequence to people who weighed 8, 9 or 10 pounds.