Symptoms of aging

One can catalog changes that typically occur with age. For people of developed countries age changes include: A loss of hearing ability, particularly for higher frequencies.

There is a decline in the ability to taste salt&bitter (sweet&sour are much less affected). There is a reduction of the thymus gland to 5−10% of its original mass by age 50. Levels of antibodies increase with aging.

One third of men and half of women over 65 report some form of arthritis. About half of those aged 65 have lost all teeth. The elderly require twice as much insulin to achieve the glucose uptake of the young. There is reduced sensitivity to growth factors & hormones due to fewer receptors and dysfunctional post-receptor pathways.

The temperature needed to separate DNA strands increases with age. Weight declines after age 55 due to loss of lean tissue, water and bone (cell mass at age 70 is 36% of what it is at age 25). Body fat increases to age 60.

Muscle strength for men declines 30−40% from age 30 to age 80. Reaction time declines 20% from age 20 to 60. Elderly people tend to sleep more lightly, more frequently and for shorter periods — with a reduction in rapid eye-movement(REM)sleep. Neurogenesis in the hippocampus declines with age. Degree of saturation of fats drops by 26% in the brains of old animals. Presbyopia(reduced ability to focus on close-up objects)occurs in 42% of people aged 52−64, 73% of those 65−74 and 92% of those over age 75. Most people over age 75 have cataracts. About half of those over 85 are disabled(defined as the inability to use public transportation). Over 75% of people over 85 have 3−9 pathological conditions, and the cause of death for these people is frequently unknown.

Aging changes are frequently associated with an increase in likelihood of mortality, but this is not necessarily the case. For example, graying of hair is a symptom of aging, but graying does not increase likelihood of mortality. Aging changes which are not associated with a specific disease, but which are associated with a generalized increase in mortality would qualify as biomarkers of aging — and would distinguish biological age from chronological age.

Biomarkers would be better predictors of the increased likelihood of mortality(independent of specific disease)than the passage of time(chronological age). Cross-linking of collagen, insulin resistance and lung expiration capacity have been proposed as candidates but, as yet, no biomarkers of aging have been validated and universally accepted.