As we get older, the aging process affects our bodies in many ways. While aging is inevitable, the rate at which different parts of our body show signs of aging can vary significantly. When we think about aging, visible signs like wrinkles, gray hair, and joint pain often come to mind first. But aging starts on a cellular level, long before outward signs appear. So what part of the body actually ages first? There are a few key contenders.
Brain
Many experts believe the brain shows signs of aging earlier than any other part of the body. Some brain aging processes begin as early as our 20s and 30s. After reaching full maturity in our early 20s, the physical size and weight of our brains gradually decrease with age. Brain volume, the amount of tissue in the brain, starts to decline around age 30 at a rate of about 5% per decade. Certain parts of the brain shrink faster than others, including the frontal lobe and hippocampus which are involved in thinking, planning, and memory formation.
In addition to losing volume, our brains develop more inflammation with age and accumulate wastes like amyloid plaques and tau tangles. Reduced blood flow in the brain can also impair cognitive skills. These physical changes correlate with declining cognitive abilities like:
- Processing speed
- Memory
- Learning new information
- Focus and concentration
- Reasoning
While a certain amount of cognitive decline is normal with healthy aging, dementia and Alzheimer’s disease represent more extreme brain aging processes that rob individuals of their memory, skills, and independence.
Heart
After the brain, the heart and cardiovascular system are often considered the next parts of the body to show age-related changes. Some subtle signs of a declining cardiovascular system may begin in our 30s. The most notable changes involve stiffening and reduced flexibility of the heart and blood vessels. These changes raise the risk for high blood pressure and heart disease. Specific aging processes for the heart and circulation include:
- Increased rigidity and thickening of the heart’s walls
- Decline in the maximum heart rate and cardiac output during physical activity
- Stiffening of the arteries
- Higher risk for arrhythmias and abnormal heart rhythms
On average, the maximum heart rate drops by about one beat per minute per year. So a 40 year old’s maximum heart rate would be around 180 beats per minute while a 70 year old’s would be closer to 140 beats per minute. The quantity of blood pumped by the heart (cardiac output) also declines by about 1% per year in healthy adults. In addition to changes in the heart itself, arteries stiffen with age which increases blood pressure and the load on the heart.
Lungs
Lung capacity and function reaches its peak in our late teens to early 20s. After this point, our lungs gradually lose strength and performance. Factors like reduced muscle strength, stiffness of chest wall muscles and joints, and weakened respiratory muscles contribute to reduced lung function. Beginning around age 35, the lungs lose elasticity and the chest cavity stiffens. Typical lung function decrease is:
- Total lung capacity decreases by about 5% per decade
- Maximum breathing capacity (VO2 max) decreases by 1% per year
- Strength of respiratory muscles declines 1% per year
Gas exchange efficiency in the lungs also decreases with age due to the lungs losing their ability to fully empty and fill with air. Older lungs contain more dead space, which is air that doesn’t participate in gas exchange. Therefore, more air must be inhaled and exhaled with each breath. By age 65, about 40% of inhaled air remains in areas of the lung where gas exchange cannot occur, compared to about 25% in young adults.
Kidneys
After age 30, the kidneys start to decline in function at a rate of about 1% loss per year. This decline includes reduced blood flow to the kidneys as well as loss of nephrons, the kidney’s filtering units. Nephron number decreases from 0.8-1.2 million at birth to 0.6-1 million by age 80. With fewer functioning nephrons, the remaining nephrons have to work harder. Kidney aging processes include:
- Decline in glomerular filtration rate (GFR)
- Tubule loss and atrophy
- Increased rigidity of blood vessels supplying the kidneys
- Decreased kidney mass
These changes lead to decreased water and salt regulation by the kidneys. Conditions like high blood pressure and diabetes can accelerate kidney aging. The effects of reduced kidney function accumulate so even mild changes early on can increase the risk of more severe kidney disease later in life.
Bones and Joints
Osteoporosis is a common age-related condition characterized by weak, brittle bones that become more prone to fracture. After age 30, bone density begins decreasing as bone is lost more rapidly than it can be rebuilt. In addition to reduced bone density and strength, aging affects joints through:
- Cartilage loss and erosion
- Changes in synovial fluid that lubricates joints
- Stiffening of ligaments
- Weakened muscles surrounding joints
These joint changes lead to common problems like osteoarthritis, rheumatoid arthritis, and loss of flexibility or mobility. The spine is especially vulnerable to arthritis and degeneration from factors like disc desiccation, herniation, and osteophyte formation. Posture and strength deterioration of back muscles can further contribute to back pain.
Skin
Some of the first obvious outward signs of aging include wrinkles, age spots, sagging skin, and uneven pigmentation. Under the skin’s surface, additional anatomical changes occur with aging:
- Decline in collagen production
- Loss of elastin fibers
- Thinning epidermis
- Reduced skin cell turnover
- Decreased vascularity and blood supply
- Loss of subcutaneous fat
- Decreased sweat and oil gland activity
These factors combine to make skin more prone to drying, injury, healing issues, and irritation with age. Skin can become thinner, looser, and more transparent over time. Exposure to UV radiation accelerates skin aging. The face is often one of the first visible indicators of skin aging though the decline in collagen fibers weakens skin throughout the body.
Digestive System
Multiple aspects of the digestive system decline with age such as:
- Reduced production of saliva
- Less efficient chewing and swallowing
- Decreased nutrient absorption
- Lower muscle tone in digestive tract
- Impaired ability to break down and metabolize certain nutrients
The glands secreting saliva and digestive enzymes produce less output. This can contribute to difficulty swallowing and properly breaking down food. GI motility slows down resulting in more constipation issues. Increased inflammation in the GI tract may also negatively impact digestion. Capacity to absorb certain nutrients like vitamin B12, calcium, and vitamin D decreases with the aging digestive system. These malabsorption issues then influence nutritional status.
Immune System
Age-related changes to the immune system reduce its effectiveness in fighting off pathogens and infections. This immune system decline is called immunosenescence. Some characteristic effects of an aging immune system include:
- Reduced production of B and T cells from bone marrow
- Decreased activity of natural killer cells
- Lower antibody response to vaccines and infections
- More autoantibodies leading to increased autoimmune reactions
- Increased proinflammatory cytokines
- Oxidative damage shortening telomeres of lymphocytes
While young people often quickly recover from colds or the flu, older adults tend to take longer to fight off infections. Immunosenescence makes seniors more vulnerable to pneumonia, influenza, COVID-19, shingles, cancer and other diseases an optimal immune system could combat. Declining thymus gland activity with age also reduces production of immune cells.
Vision and Hearing
Sensory organs and systems deteriorate with age resulting in vision loss and hearing impairment:
- Eyes – Decreased pupil size, tear production, and accommodation. Increased clouding of eye lenses and higher risk for disorders like glaucoma, cataracts, and macular degeneration. Near vision becomes harder beginning around age 40.
- Ears – Loss of hair cells and nerve endings in the inner ear makes it harder to hear high pitched tones and filter sounds. Hearing problems start as early as age 20 with increasing difficulty hearing faint sounds and distinguishing words.
Presbyopia makes reading small print harder while presbycusis causes difficulty understanding conversations, especially in noisy environments. Certain medications and environmental factors like smoking can expedite loss of vision and hearing.
Reproductive System
For women, declining fertility generally begins in their 30s as egg quality and number start to decrease. Menopause, marking the end of the reproductive years, usually occurs between ages 45-55. The hormonal changes involved influence the aging process in tissues throughout the body. In men, testosterone levels peak around age 30 then slowly decline by 1-2% per year. The prostate gland also enlarges in most men by age 60. Lower testosterone can reduce muscle mass, bone density, libido, energy, and cognitive functions. However, sperm quality deteriorates much later, generally not until around age 80.
Muscles
Muscle mass, strength and endurance all decline with aging due to factors like:
- Loss of fast twitch muscle fibers
- Smaller motor units
- Reduced protein synthesis
- Decreased circulation and blood flow
- Loss of neurons innervating muscles
- Hormonal changes
- Less physical activity
Loss of muscle mass and strength, known as sarcopenia, accelerates after age 50. Muscles throughout the body weaken but those in the arms, legs, and core can display substantial decline. The muscles involved in breathing and posture are also affected. This muscle deterioration often leads to frailty, mobility issues, and loss of independence.
Stem Cells
All organs and tissues depend on stem cells to maintain their regenerative capacity. But stem cells decline in number and lose their proliferative abilities with aging. Reduced stem cell activity impairs the body’s ability to renew itself. Early aging of stem cells reduces availability of progenitor cells to replace damaged or malfunctioning cells. For example, muscle stem cells decline with age leading to reduced muscle repair after injury. Declining hematopoietic stem cells in the bone marrow lead to impaired immune function. The proliferative potential of neural stem cells also declines. With fewer functioning stem cells, organs have a decreased ability to regenerate after injury or disease.
Telomeres
Telomeres are structures at the end of chromosomes that protect DNA integrity but shorten each time a cell divides. As telomeres get progressively shorter with aging, cells lose their ability to replicate and die instead. Telomere shortening is associated with many age-related diseases and early mortality. Maintaining telomere length may promote longevity and healthspan. Factors like chronic stress and inflammation, smoking, obesity, inactivity, and malnutrition can accelerate telomere attrition.
Hormones
Declining hormonal activity influences many aspects of aging throughout the body. For example, growth hormone and IGF-1 decrease leading to reduced muscle and bone mass. Reproductive hormone levels (estrogen, progesterone, testosterone) fall with impacts on the reproductive system as well as metabolic processes, cognition, and more. The adrenal glands produce lower levels of DHEA, an adrenal androgen with systemic effects. Insulin sensitivity decreases, potentially contributing to higher diabetes risk. These types of hormonal changes start gradually but accumulate developmental effects over decades.
Cellular Changes
Aging occurs right down to the cellular level. Key cellular aging processes include:
- Accumulation of metabolic wastes and damage
- Increased inflammation
- Decline in mitochondria function
- Impaired protein processing
- Shortened telomeres
- DNA damage
- Chromosome changes
- Epigenetic alterations
- Cellular senescence
- Stem cell exhaustion
These changes impair cell replication, communication, and proper tissue function. Loss of proteostasis, where cells have difficulty regulating proteins, contributes to many age-related disorders. Changes build up over decades leading to biological aging. Cells accumulate toxic aggregates and struggle to break down defective parts, remove waste, and maintain defenses against stress.
Conclusion
In summary, while outward aging signs tend to appear first on the skin and hair, internal changes actually begin much sooner in organs and tissues throughout the body. Brain atrophy leading to cognitive decline gets underway as early as young adulthood. Cardiovascular aging processes, lung capacity reduction, immune dysfunction, and kidney deterioration all start by around age 30-35 in healthy adults. So functionally, the brain, heart, lungs, and kidneys show early signs of aging.
Musculoskeletal aging follows shortly thereafter with reduced bone density and joint cartilage changes beginning in a person’s 30s and 40s. Skin changes like wrinkles and uneven pigmentation usually start to crop up in a person’s 40s as collagen production declines. Vision and hearing impairment often doesn’t become noticeable until around age 50. Declining fertility generally starts in a woman’s 30s while testosterone reduction begins in men around age 30, but reproductive aging processes continue gradually for decades.
Aging progresses concurrently in multiple parts of the body driven by interconnected cellular and molecular changes like oxidative stress, inflammation, telomere attrition, epigenetic shifts, and declining proteins, mitochondria, hormones, stem cells, and more. These systemic factors contribute to tissue dysfunction and the clinical signs of aging. While genetic influences play a role, lifestyle choices and environmental exposures can either accelerate or help decelerate the aging process.
