Aging changes

Aging is the time-related progressive functional decline that affects all organ systems. It is believed to be caused by the accumulation of DNA damage, hormonal changes, and internally programmed cellular changes. Effects of aging include stiffening of the arteries and calcification of valves (cardiovascular system), osteoporosis and increased risk of fracture (musculoskeletal system), decreased chest wall compliance and increased ventilation-perfusion mismatch (respiratory system), susceptibility to recurrent infections and malignancies (immune system), and decline in cognitive function and changes in sleep patterns (nervous system).

All cells are subject to the natural processes of aging. Aging is believed to be caused by the accumulation of DNA damage, hormonal changes, and internally programmed cellular changes. Aging affects all organ systems and leads to progressive functional decline.

Aging changes in the bones, muscles, and joints

• Increased bone resorption and osteoporosis, increased risk of fracture (♀ > ♂)
  • Postmenopausal osteoporosis: decreased estrogen levels → increased bone resorption
  • Senile osteoporosis; (especially in individuals > 70 years): decreased osteoblast activity → decreased osteoid production
• Decreased lean body mass due to atrophy and loss of muscle cells (sarcopenia)
• Degenerative changes in joints: stiffer and less flexible joints, decreased synovial fluid and cartilage, calcification (e.g., in the shoulder), height loss

Regular exercise and a diet rich in protein, vitamin D, creatine, and omega-3 fatty acids are essential to ensure muscle growth and help prevent sarcopenia!

Aging changes in the skin

There is an increased incidence of:

• Noncancerous skin growths such as:
  • Seborrheic keratosis
  • Keratoacanthomas
• Cancerous growths such as basal cell cancer and squamous cell carcinoma
• Skin tags, warts, liver spots, solar lentigo
• Hyperpigmented macules due to cutaneous deposition of lipofuscin (typically in the face and dorsum of hand)
• Xerosis cutis and pruritus due to decreased lipid and sebum synthesis and increased moisture loss
• Heatstroke due to decreased number of sweat glands
• Wrinkles due to:
  • Decreased elastin synthesis → increased skin laxity and rigidity
  • Decreased collagen synthesis → atrophy of the dermis → wrinkle formation and decreased strength → increased risk of skin damage (e.g., decubitus and bruises )
  • Increased crosslinking of elastin and collagen → skin stiffness and decreased elastic recoil (elastosis) ^[1]
  • Decreased glycosaminoglycan (including hyaluronic acid) synthesis → decreased dermal moisture retention → decreased dermal volume
  • Decreased subdermal fat → skin sagging and risk of hypothermia

Aging changes in the nails and hair

• Nails
  • Become more brittle and may become yellowed
  • Toenails may become thicker
  • Ingrown toenails and onychomycosis are more common
• Hair: graying, baldness (see “Male pattern hair loss” and “Female pattern hair loss”)

Aging changes in the cardiovascular system

• Vascular sclerosis and stiffness→ increased systolic blood pressure
• Left ventricular hypertrophy and progressive stiffening with a 10% increase in wall size
• Mitral and aortic valve thickening and calcification
• Marked decline in stress-induced and exercise-induced maximal heart rate due to decreased response to the action of catecholamines
• Lipofuscin deposits in cardiac muscle

Aging changes in the respiratory system ^[2]

Aging changes in the genitourinary system

• Kidneys
  • Decreased glomerular filtration rate (GFR), diffuse sclerosis of glomeruli
  • Decreased renal mass and replacement of parenchyma by fat and fibrosis, predominantly in the renal cortex → decreased maximal concentrating ability
  • Decreased number of nephrons
  • Decreased acid load excretion
• Urinary and sexual
  • Increased urinary frequency and urgency
  • Increased risk of urinary tract infection
  • Decrease in libido (typically more pronounced in women than men)
  • Women
    • Postmenopausal estrogen deficiency leading to:
      • Vaginal atrophy, dryness, and irritation
      • Increased risk of yeast infections and other UTIs
      • Possibly dyspareunia
    • Decreased tone of pelvic floor muscles → prolapse of vagina, uterus, or bladder
  • Men
    • Testicular atrophy
    • Enlarged prostate gland
    • Slowed urination, erection, and ejaculation
    • Increased refractory period

Aging changes in the immune system ^{[3][4][5][6][7][8]}

• Impaired immune response and regulation of inflammation predispose individuals to recurrent infection, impaired wound healing, malignancy, and autoimmune disease.
• Decreased antibody and cell-mediated immune responses to a new antigen
  • A decline in the counts of most subsets of B cells and T cells (exception: memory T-cell and memory B-cell counts increase)
  • Decreased affinity of antibodies for new antigens
    • Decrease in the variety of B-cell receptors for antigens
    • Increase in the proportion of monoclonal cell lines
    • Impaired affinity maturation and impaired V(D)J recombination
• Total immunoglobulin level remains the same.
• Macrophage and neutrophil counts do not decrease but they are less effective in their functions (e.g., phagocytosis).
• Increased number of NK cells, PGE₂, and increased autoantibody production

Among the elderly, a decreased immune response leads to an increased need for booster vaccinations.

Aging changes in the endocrine system

• Decreasing hormones
  • Calcitonin, growth hormone, renin, aldosterone, melatonin (loss of normal circadian rhythms)
  • Estrogen and prolactin in women (e.g., contributes to breast atrophy)
  • Testosterone gradually decreases in men.
• Increasing hormones: FSH, LH, norepinephrine, parathyroid hormone (contributes to osteoporosis)

Aging changes in the nervous system

• Presbycusis: progressive high-frequency hearing loss due to loss of hair cells at the base of the cochlea
• Presbyopia: impaired accommodation (near object focusing) due to decreased elasticity of the lens; decreased ciliary muscle strength
• Decline of vertical gaze and convergence ^[9]
• Decreased sense of smell and taste
• Reduced ability to detect vibration, touch, temperature, and pressure changes (increased risk of pressure ulcers, hypothermia, and burns)
• Decreased/absent deep tendon reflexes (e.g., ankle jerk reflex)
• Decreased cerebral blood flow and brain volume
• Fluid intelligence declines, whereas crystallized intelligence increases
• Altered sleep patterns: early morning awakening, later sleep onset, decreased REM, and decreased slow-wave sleep
• After the 6^th decade of life
  • Decline in executive function, working memory, processing speed, and attention span
  • In most cases, no clinically significant impairment in social and occupational functioning
  • Increased suicide risk in case of physical and mental illnesses (particularly depression), functional impairment, and stressful life events (e.g., loss of a partner)