40.1 Growth and Development Stages

Physiological Development

Physiological and physical development changes continue throughout young adulthood. Body size and physical appearance are consistent with an adult stage, and growth velocity slows and stabilizes. In healthy young adults, organ systems are functioning at the highest capacity. Young adults can maximize energy output and have significant physical endurance. The following are some physiological processes that are at their peak in early adulthood:

• lung function
• cardiac function
• agility
• flexibility
• vision
• hearing
• reproduction

Health in young adulthood can vary significantly from one individual to another. Peak ability and physiological performance depend on underlying chronic health disorders, genetic factors, and lifestyle choices. The body is highly adaptable and may compensate to a certain degree for poor lifestyle choices during this stage. However, there is an epidemic of obesity and inactivity spanning the adolescent and young adult population. Lifestyle choices, such as unhealthy eating habits, lack of exercise, or substance use disorders, can have significant negative short- and long-term effects on health (Zheng et al., 2017). While young adults may have a certain level of resilience, chronic poor lifestyle choices can increase the risk of developing various health issues later in life, such as obesity, cardiovascular disease, and diabetes. It is important for individuals to prioritize healthy behaviors and habits from a young age to promote long-term health and well-being. While individuals may still experience their personal best health during their early adulthood, they may be in comparatively poor health due to the presence of chronic diseases such as obesity, type 2 diabetes, and depression. These increasingly prevalent disorders are often interrelated and associated with a sedentary lifestyle (Lawrence et al., 2017; Zheng et al., 2017).

In the later part of young adulthood, organ systems start a slow, gradual decline. By the mid to late 30s, young adults start noticing signs of aging. These signs may include a decline in immune function, sensory response time, agility in movement, and ability to recover quickly from physical exertion. For example, running or other physical exercise may cause individuals to feel winded longer after stopping an activity. While many physical changes occur and some physical decline is expected with age, individuals of all abilities can experience the benefits of maintaining physical activity throughout their life span. Finding joyful body movement that fits one’s abilities, preferences, and lifestyle shows a commitment to maintaining health.

Psychological Development

During the stage of emerging adulthood, very young adults work through a process of emerging as adults. Significant brain development continues throughout this stage of adulthood, which occurs immediately after adolescence and typically lasts until around the age of 25 years (Wood et al., 2017). Young adults experience significant behavioral and social maturation during this time, during which they are expected to perform as adults. Brain maturation continues through early adulthood and includes increases in brain white matter and development and integration of the frontal and prefrontal cortex of the brain. Behavior changes associated with these brain developments include the following (Hochberg & Konner, 2020):

• decreased aggression
• impulse control
• role changes

Many of these psychological changes occur in response to the development of the frontal cortex, which controls executive functioning—the ability to develop plans, focus attention, perform from working memory, maintain self-awareness, initiate and execute complicated tasks, control impulses, and manage emotions. As individuals progress through young adulthood, they typically experience significant improvement in executive functions that are based on both life experiences and the completion of brain development. Individuals may notice improved parenting skills, ability to function in a work environment, and coping skills to manage life stressors.

Young adults are highly capable of learning new and complex ideas and tasks. As the white matter in the brain develops, communication improves within and between brain regions. Therefore, young adults have a high capacity for integrating new information, generating new ideas, and synthesizing information (Harvard University, n.d.).

Young adult brain development is affected by stress, life chaos, physical or emotional threats, and unpredictable environments. In addition, habits like food choices, screen use, and substance use influence brain neurotransmitters, including dopamine. For example, in some cases, video gaming can positively affect reaction time and cognitive plasticity—the ability of the brain to adapt to new experiences. However, recent studies have shown that due to dopamine production and release during gaming, playing for more than three hours per day can increase the risk for attention problems, depression, and attention deficit hyperactivity disorder (ADHD) symptoms. These results apply to children and emerging adults whose prefrontal cortex is still developing (National Institutes of Health [NIH], 2022). Screen use of any type has been shown to affect sleep onset, duration, and quality of REM sleep, which is essential for activating memory and storing information. Variable reward systems are unpredictable psychological rewards that provide a dopamine surge in the brain and encourage individuals to pursue additional gratification (Haynes, 2018). Variable rewards are associated with social media and gaming and may challenge some young adults who lack the self-control needed to limit their screen use (Harvard University, n.d.).

Psychosocial Development

Young adults begin the transition to adulthood at approximately age 18 years. Following are some of the many social cues that mark the progression to adulthood:

• obtaining a driver’s license
• becoming eligible to vote
• going to college
• joining the military
• reaching the legal drinking age

Cultural cues that indicate a progression toward or into adulthood vary widely among cultures or families but may include the following:

• buying a car
• moving out of their parents’ home
• dating
• getting married
• having children
• buying a house

These social and cultural guideposts are not universally experienced, and individuals who do not attain them can still progress through early adulthood. Since the timeline associated with reaching adulthood is highly individual, it has been proposed that there is a new stage of development between adolescence and early adulthood called “emerging adulthood.” During this time, young people do not yet identify with adulthood. Therefore, they may wait longer to join the workforce, move out on their own, get married, and/or have children. However, by the end of early adulthood, most individuals will have accomplished the core developmental tasks of becoming more autonomous, taking care of themselves and others, committing to relationships and jobs/careers, getting married, raising families, and integrating into their chosen communities. Healthy lifestyle habits such as adequate nutrition, exercise, positive social interaction, and moderating digital and social media use during young adulthood affect health during the next stage.

Physiological Development

During middle adulthood, individuals continue to notice signs of aging, although these may be more subtle or more pronounced depending on individual characteristics and life choices (Table 40.1). Expected changes occur in various organ systems, including the following:

• musculoskeletal
• cardiovascular
• integumentary
• gastrointestinal
• urinary
• sensory
• dental
• reproductive

Reproductive

The cessation of the menstrual cycle for at least twelve months is known as menopause. It is a period of transition during which the ovaries stop releasing eggs, and the level of estrogen and progesterone production decreases. Menopause typically occurs during middle adulthood, though some individuals experience abnormal early menopause in young adulthood. After menopause, menstruation ceases. Menopause primarily ends an individual’s natural ability to conceive a child, but the hormonal changes also affect other organ systems (Figure 40.2). Changes during menopause and perimenopause, the stage preceding menopause, can include direct physical changes to organs and tissue, such as vaginal dryness and atrophy associated with estrogen reduction, lower libido, and hot flashes.

Figure 40.2 Persons assigned female at birth may experience a wide range of symptoms during menopause. (credit: modification of “Symptoms of menopause (vector)” by Mikael Häggström/Wikipedia, CC0 1.0 Public Domain)

Menopause is not seen as universally distressing (Brown et al., 2021). Changes in hormone levels are associated with hot flashes and sweats in some people; however, the intensity, duration, and frequency of these symptoms vary. Other symptoms like depression, irritability, and weight gain are not necessarily caused by menopause (Brown et al., 2021). The incidence of depression and mood swings is not greater among menopausal people than nonmenopausal people.

Patient Conversations

Hormone Replacement in Menopause

Scenario: Jenell is a 50-year-old eighth-grade teacher who spends her free time traveling with her husband and two teenage sons, hiking and skiing with her dog, and studying history. She sees her primary care provider yearly for a wellness checkup. She has made an appointment with her provider to discuss unexpected weight gain and other menopausal changes. Anna works as a nurse in the primary care medical office, where Jenell is a patient. While Anna takes her vital signs, Jenell states, “I’m in menopause, so I guess it’s time to start hormones.” Anna remembers that only a small percentage of persons AFAB experiencing natural menopause take hormone replacement therapy.

Nurse: Are you still having a menstrual cycle? What symptoms are you experiencing with menopause?

Patient: My last period was fourteen months ago. I have noticed some weight gain, even though I’m pretty active. I have some irritability and feel down a lot. I have had a few hot flashes, but nothing really bothersome, not like what my friends tell me about. Another big concern is painful intercourse. I know some friends who are taking herbal supplements, but I thought it was just best to get on a hormone replacement.

Nurse: There are many ways to cope with menopausal changes, including hormone replacement therapy. Some people take a supplement for a short time, others only use topical hormone treatments, and some use no hormones at all. It all depends on your symptoms.

Patient: I want to hear my options. I’d rather not take a hormone if I don’t need to.

Nurse: I’ll let your provider know your symptoms, and you can discuss the options. For example, they might suggest medication that affects serotonin to help with emotional symptoms and hot flashes as well as a vaginal cream to improve vaginal lubrication and skin elasticity.

A reduction in testosterone production in males is called andropause. While the reduced hormone production does not affect their overall ability to reproduce, it may cause changes in libido, body hair, loss of muscle mass, and breast enlargement. Adult persons AMAB can experience erectile dysfunction at any age and for a variety of reasons, but it is more common as they age, due to factors such as stress, lack of physical activity, obesity, and chronic underlying health issues.

Psychological Development

Physiological changes may affect psychological health at all life stages, and vice versa. The psychological developments in middle adulthood relate to prior life circumstances, including childhood experiences and life choices made during young adulthood.

Middle-aged adults may experience significant daily stress related to family disputes, work overload, raising children, and caregiving for aging parents. Exacerbations of depression symptoms may be triggered by specific stressors, including death, divorce, job changes, or unemployment. Psychological well-being is also associated with lifestyle choices.

In the later part of middle adulthood, individuals may begin to experience mild cognitive impairment and memory loss. Hormones that affect sleep may worsen cognition and mental health management. Depression and anxiety early in life may be exacerbated during the middle-life stage due to increasing life and social stressors and worries about finances, health, and family (Brown et al., 2021). Middle-aged adults continue accumulating crystallized intelligence, the ability to draw and extrapolate from previously learned experiences (Perera, 2024). However, fluid intelligence, the ability to reason, transform, or generate new information, may decrease during middle age (Perera, 2024). The effects of knowledge, experience, and increased ability to regulate emotions can compensate for these losses.

Brain science is evolving and will provide new insights about cognition in midlife, such as the brain’s capacity to renew, or at least replenish, itself (Mayo Clinic, 2024). The capacity to renew brain connectivity through new connections is called neurogenesis, while the capacity to replenish or strengthen existing connections is called neuroplasticity. Disease states such as depression, high blood pressure, and sleep apnea; alcohol; as well as medication interventions such as opioids, benzodiazepines, antihistamines, and proton pump inhibitors may affect cognitive outcomes (Mayo Clinic, 2024).

Working memory, or the ability to simultaneously store and use information, becomes less efficient with age (Craik & Bialystok, 2006). The ability to process information quickly also decreases with age. The slowing of processing speed may explain age-related variations in the performance of different cognitive tasks (Salthouse, 2004). Some researchers have argued that inhibitory functioning, or the ability to focus on certain information while suppressing attention to less pertinent information, declines with age and may explain why performance on cognitive tasks tends to vary by age (Hasher & Zacks, 1988).

Psychosocial Development

Middle adulthood typically involves establishing one’s career and contributing to others’ development through activities like volunteering, mentoring, and raising children (Infurna et al., 2020). During this stage, middle-aged adults may begin contributing to the next generation, often through caring for others. Often, they also engage in meaningful and productive work that contributes positively to society (Infurna et al., 2020). During this time, adults also experience a range of interpersonal challenges, such as the following:

• coping with the death of parents and associated grief
• supporting children as they move on into their own lives
• adjusting to home life without children (often referred to as the “empty nest”)
• supporting adult children who return to live at home (known as “boomerang children” in the United States)
• becoming grandparents
• preparing for late adulthood
• acting as caregivers for aging parents or spouses
• experiencing workplace satisfaction/dissatisfaction

Some psychosocial theorists believe that the early years of middle adulthood are a time for reappraisal or, perhaps, the reaffirmation of goals, commitments, and previous choices. It can be a time for taking stock and recalibrating what is important in a person’s life. This new perspective on time brings a sense of urgency to life. A person focuses more on the present than the future or the past. They may grow impatient with being in the “waiting room of life,” postponing doing things they have always wanted to do. A previous focus on the future gives way to an emphasis on the present. Neugarten (1968) notes that in midlife, people no longer think of their lives in terms of how long they have lived. Rather, life is thought of in terms of how many years are left. If an adult is unsatisfied at midlife, there is often a heightened motivation to make changes “before it’s too late.”