Public Health and the Second 50 Years of Life

Aging is the maturation and senescence of biological systems. With each additional decade of life, adults will see a number of changes, for example, a slowing in reaction time, psychomotor speed, and verbal memory; declines in strength and walking speed; a decreased rate of urine flow; loss of skeletal muscle; and, of course, greater mortality. They will also see declines in addictive behaviors and crime; a reduction in severe psychiatric disorders; stability in psychological well-being; continuing increases in vocabulary; greater selectivity in friendship and increased contact with close family; less need for novel stimuli; and increases in wealth, leisure time, and altruistic behaviors, among many other changes. The popular understanding of aging mostly stresses negative changes that result in disability, but a more complete understanding should stress both kinds of change, for both are relevant to a public health perspective on aging. These changes may be more prevalent in older people because they are, in fact, true expressions of senescence. Or they may be more prevalent simply because of the greater length of time older people have lived, and hence the greater opportunity they have had to experience the risks or exposures that produce these effects. This is a key distinction. More than likely, some combination of true senescence and greater exposure to risk factors is likely to be responsible for the changes we consider “aging.” For example, the highest audible pitch people can hear declines with age, suggesting that this change is a senescent feature of the auditory system. But it is also likely that long years of occupational exposure to noise, untreated ear infections during childhood, neurological conditions, and an accumulation of minor injuries might contribute to loss of hearing in old age. What happens in the first half of life must surely matter to health in the second half.