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Source: The Washington Post
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Critics:
A number of characteristic signs and symptoms of ageing are experienced by a majority, or by a significant proportion of humans during their lifetimes. These age-related changes can vary in different bodily systems and among individuals, a heterogeneity referred to as ‘mosaic ageing’.
- Teenagers tend to lose the young child’s ability to hear high-frequency sounds above 20 kHz.
- Wrinkles develop mainly due to photoageing, particularly affecting sun-exposed areas such as the face.
- After age 35, female fertility falls rapidly.
- Most people experience presbyopia by age 45–50. The cause is lens hardening by decreasing levels of alpha-crystallin, a process which may be sped up by higher temperatures. An alternative theory is loss of strength in the ciliary muscle of the eyes.
- By age 55, hair tends to grey.
- Pattern hair loss by the age of 55 affects about 30–50% of males and a quarter of females.
- Menopause typically occurs between 44 and 58 years of age.
- In the 60–64 age cohort, the incidence of osteoarthritis rises to 53%. Only 20%, however, report disabling osteoarthritis at this age.
- Almost half of people older than 75 have hearing loss (presbycusis) inhibiting spoken communication. Many vertebrates such as fish, birds and amphibians do not develop presbycusis in old age, as they are able to regenerate their cochlear sensory cells; mammals, including humans, have genetically lost this ability.
- By age 80, more than half of all Americans either have a cataract or have had cataract surgery.
- Frailty, a syndrome of decreased strength, physical activity, physical performance and energy, affects 25% of those over 85. Muscles have a reduced capacity of responding to exercise or injury and loss of muscle mass and strength (sarcopenia) is common. Maximum oxygen use and maximum heart rate decline.Hand strength and mobility decrease.
- Atherosclerosis is classified as an ageing disease. It leads to cardiovascular disease (for example, stroke and heart attacks), which, globally, is the most common cause of death. Vessel ageing causes vascular remodelling and loss of arterial elasticity, and as a result, causes the stiffness of the vasculature.
- The maximum human lifespan is suggested to be around 115 years. The oldest reliably recorded human was Jeanne Calment, who died in 1997 at 122 years of age.
Dementia becomes more common with age. About 3% of people between the ages of 65 and 74, 19% of those between 75 and 84, and nearly half of those over 85 years old have dementia. The spectrum ranges from mild cognitive impairment to the neurodegenerative diseases of Alzheimer’s disease, cerebrovascular disease, Parkinson’s disease and Lou Gehrig’s disease.
Furthermore, many types of memory decline with ageing, but not semantic memory or general knowledge such as vocabulary definitions. These typically increase or remain steady until late adulthood . Intelligence declines with age, though the rate varies depending on the type and may, in fact, remain steady throughout most of the human lifespan, dropping suddenly only as people near the end of their lives.
Individual variations in the rate of cognitive decline may therefore be explained in terms of people having different lengths of life. There are changes to the brain: after 20 years of age, there is a 10% reduction each decade in the total length of the brain’s myelinated axons. Age can result in visual impairment, whereby non-verbal communication is reduced, which can lead to isolation and possible depression.
Older adults, however, may not experience depression as much as younger adults, and were paradoxically found to have improved mood, despite declining physical health. Macular degeneration causes vision loss and increases with age, affecting nearly 12% of those above the age of 80. This degeneration is caused by systemic changes in the circulation of waste products and by the growth of abnormal vessels around the retina.
Other visual diseases that often appear with age are cataracts and glaucoma. A cataract occurs when the lens of the eye becomes cloudy, making vision blurry; it eventually causes blindness if untreated. They develop over time and are seen most often with those that are older. Cataracts can be treated through surgery. Glaucoma is another common visual disease that appears in older adults. Glaucoma is caused by damage to the optic nerve, causing vision loss.
Glaucoma usually develops over time, but there are variations to glaucoma, and some have a sudden onset. There are a few procedures for glaucoma, but there is no cure or fix for the damage, once it has occurred. Prevention is the best measure in the case of glaucoma. The rate of ageing varies substantially across different species, and this, to a large extent, is genetically based.
For example, numerous perennial plants ranging from strawberries and potatoes to willow trees typically produce clones of themselves by vegetative reproduction and are thus potentially immortal, while annual plants such as wheat and watermelons die each year and reproduce by sexual reproduction. In 2008 it was discovered that inactivation of only two genes in the annual plant Arabidopsis thaliana leads to its conversion into a potentially immortal perennial plant.
The oldest animals known so far are 15,000-year-old Antarctic sponges, which can reproduce both sexually and clonally. Clonal immortality apart, there are certain species whose individual lifespans stand out among Earth’s life-forms, including the bristlecone pine at 5062 years or 5067 years, invertebrates like the hard clam (known as quahog in New England)
At 508 years, the Greenland shark at 400 years, various deep-sea tube worms at over 300 years, fish like the sturgeon and the rockfish, and the sea anemone and lobster. Such organisms are sometimes said to exhibit negligible senescence. The genetic aspect has also been demonstrated in studies of human centenarians…
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