What’s normal for the body and brain as we age? An expert weighs in.

Here are a few of the age-related issues she highlights in her book:

• Older people often present with different symptoms than younger people when they become ill. For instance, a senior having a heart attack may be short of breath or confused, rather than complain of chest pain. Similarly, an older person with pneumonia may fall or have little appetite instead of having a fever and cough.
• Older people often react differently than younger people to medications. Because of changes in body composition and liver, kidney and gut function, older adults are more sensitive to medications and often need lower doses. This includes medications that someone may have taken for years. It also applies to alcohol.
• Older people have reduced energy reserves. With advancing age, hearts become less efficient, lungs transfer less oxygen to the blood, more protein is needed for muscle synthesis, and muscle mass and strength decrease. The result: Older people tend to have less energy than in the past, even as they need more energy to perform everyday tasks. Hunger and thirst decline. People’s senses of taste and smell diminish, lessening food’s appeal. Loss of appetite becomes more common, and seniors tend to feel full after eating less food. The risk of dehydration increases.
• Cognition slows. Older adults process information more slowly and work harder to learn new information. Multitasking becomes more difficult, and reaction times grow slower. Problems finding words, especially nouns, are typical. Cognitive changes related to medications and illness are more frequent. These changes are normal and do not signify the onset of dementia.
• The musculoskeletal system is less flexible. Spines shorten as the disks that separate the vertebrae become harder and more compressed; older adults typically lose 1 to 3 inches in height as this happens. Balance is compromised because of changes in the inner ear, the brain and the vestibular system (a complex system that regulates balance and a person’s sense of orientation in space). Muscles weaken in the legs, hips and buttocks, and range of motion in joints contracts. Tendons and ligaments aren’t as strong, and falls and fractures are more frequent as bones become more brittle.
• Eyesight and hearing change. Older people need much more light to read than younger people. It’s harder for them to see the outlines of objects or distinguish between similar colors as color and contrast perception diminishes. With changes to the cornea, lens and fluid within the eye, it takes longer to adjust to sunlight as well as darkness.
• Because of accumulated damage to hair cells in the inner ear, it’s harder to hear, especially at high frequencies. It’s also harder to understand speech that’s rapid and loaded with information or that occurs in noisy environments.
• Sleep becomes fragmented. It takes longer for older people to fall asleep, and they sleep more lightly, awakening more in the night.