23.3 Aging and Disease

As you know from Chapters 17 and 20, with each passing decade homeostasis takes longer and allostatic load builds. Skin, hair, and body shape show unmistakable signs of senescence, while every internal organ ages. A stress to which younger bodies quickly adjust, such as a string of hot days or extra effort shoveling snow, could be lethal for the old.

Primary and Secondary Aging

Gerontologists distinguish between primary aging, which involves universal changes that occur with the passage of time, and secondary aging, which are the consequences of particular inherited weaknesses, chosen health habits, and environmental conditions. One researcher explains:

Primary aging does not directly cause illness, but it makes almost every disease more likely. The combination of primary and secondary aging causes morbidity and mortality.

For example, with age the heart pumps more slowly and the vascular network is less flexible, increasing the risk of stroke and heart attack. The lungs take in and expel less air with each breath, so that blood oxygen is reduced and chronic obstructive pulmonary disease is more common. Digestion slows. The kidneys become less efficient, increasing problems if people become dehydrated because they drink less—either because homeostasis is less efficient and thirst signals are muted, or perhaps in a deliberate attempt to reduce incontinence, which itself is caused by an aging renal/urinary system.

Furthermore, because of age, healing takes longer when an illness or an accident occurs. That is why young adults who contract pneumonia usually recover completely in a few weeks, but in the very old pneumonia can overwhelm a weakened body. Indeed, pneumonia often is listed as the cause of death for the oldest-old, although the underlying cause is primary and secondary aging.

The same is true for accidents of all kinds, from falls, crashes, fires, and poisons. Younger people are much more likely to recover from such insults, but 41 million people in the United States over age 65 died accidentally in 2010, making the accidental death rate for the elderly higher than for people of any other age (National Center for Health Statistics, 2012).

The data in the previous paragraph may bewilder you, since you learned in earlier chapters that more children, adolescents, and emerging adults die of accidents than of any other cause. The explanation centers on other causes of death. Because heart disease, cancers, strokes, and so on are rare earlier in life but common in late adulthood, accidents are the first cause of death from age 1 to 44 but only the eighth after age 65. Older people are more cautious than younger ones, but when injury occurs, death is more likely after age 65.

A developmental view of the relationship between primary and secondary aging harkens back to the lifelong toll of stress, as explained in Chapters 17 and 21. Allostatic load is measured by 10, or sometimes 16, biomarkers—including cortisol, C-reactive protein, systolic and diastolic blood pressure, waste-hip ratio, and insulin resistance. All of these indicate stress on the body, all increase with age, and all impair health.

Thus, measurement of allostatic load assesses the combined, long-term effect of many indicators, none of which is necessarily dangerous alone. If many of these biomarkers are outside the normal range, people become sick and die, especially when aging already has reduced organ reserve (see Figure 23.5). Thus, lifelong responses to stress create a biological burden, a load that becomes lethal.

Because of primary aging, medical intervention affects the old differently than the young. For this reason, drugs, surgeries, and so on that have been validated on young adults may be less effective on the elderly. Two examples are treatments for flu and hypertension, or high blood pressure.

The specific strains of flu that circulate are slightly different each year, so the vaccine is redesigned annually to fight whatever strains are predicted. That’s why people need flu shots every fall for the following winter. Annual immunization is particularly recommended for those over age 65, because their other infirmities make flu sometimes fatal.

The 2012–2013 vaccine protected the elderly reasonably well against the B strains of flu but provided almost no protection against the A strain, even though it protected the young (Kelvin & Farooqui, 2013). Obviously, the vaccine needs to be calibrated for age.

The importance of considering age when designing disease prevention is also apparent with medication to reduce hypertension. If systolic blood pressure in a middle-aged person is above 140, the first recommendation is diet (low salt), weight loss, and exercise. If that does not lower it, most doctors prescribe daily medication to reduce blood pressure, thus reducing the risk of strokes and heart attacks. However, the same blood pressure may affect the oldest-old differently (Sabayan et al., 2012).

Surprisingly, for some of the elderly, hypertension is protective; drugs may increase the risk of death, not decrease it. When physicians decide whether to prescribe pressure-lowering medication, they must consider the health and vitality of the person (Odden et al., 2012). The young-old may benefit; the oldest-old may not, perhaps because they are likely to experience a sudden drop in blood pressure that homeostasis is slow to fix, and that is less damaging if the drop is from high to average than from average to low.

Variation in hypertension may be one reason that anesthesia may damage an older person’s brain or cause the heart to stop. Drugs to reduce pain may also affect the elderly differently from the young. That may explain why temporary hallucinations and delirium after surgery are far more common for the old than for the young.

It is important to understand the distinction between acute and chronic illness. An acute illness is sudden and severe. A chronic illness is gradual and ongoing. Consider the leading cause of death in the United States, coronary heart disease.

A heart attack is acute. A person feels fine, and then suddenly breath becomes shallow; or an arm, jaw, or shoulder hurts; or the person feels nauseous or heaviness around the heart (like an elephant standing on your chest). All these symptoms are signs of a heart attack—if one occurs, do not wait to see if it goes away. Usually if medical intervention begins within an hour, the person survives, but because this is acute, every minute is crucial.

By contrast, heart disease is chronic. The arteries are clogged, so blood pressure is high, or the heartbeat becomes unsteady. Exercise leads to exhaustion or shortness of breath. The heart gradually weakens. Many adults are unaware of any disability but have high blood pressure or high LDL cholesterol—both signs of chronic heart disease.

Heart problems are the most common cause of death for both men and women. However, in general, women are more likely to have chronic diseases and men to have acute ones. More men die of heart attacks, more women die of heart disease.

The same gender difference is apparent for many other conditions: Women have far more arthritis, lupus, type 2 diabetes, depression, and osteoporosis, for instance. Men are not exempt from these conditions and women also die of acute illnesses, but gender rates differ worldwide.

Women live for years with chronic illness; men are more likely to die quickly when they become seriously ill. That is one reason the sex ratio in U.S. nursing homes is about 3 women for every man, even though the overall population of those over age 65 is only about 1.3 women for every man (Figure 23.6).

This distinction is problematic because hospitals, many doctors, and research funding target acute illnesses—the emergencies that have sirens wailing and surgeons running, hoping to save a life. Meanwhile, women suffer for years, with lower DALYs (disability life years), but without effective medical treatment.

Quite apart from sexism, there are historical reasons for the neglect of chronic conditions. For most of human history, when people died at much younger ages, most died of acute illness. Saving heart attack victims, preventing blood poisoning, vaccinating against typhoid—those were obvious goals that have changed. Dealing with chronic illness is the major medical challenge now.

Compression of Morbidity

Ideally, prevention of disease begins in childhood and continues lifelong, so “the target of public health and aging efforts is not just the older adults of today but the children and adults who are the future elders” (Albert & Freedman, 2010, pp. 31–32). Illness can be limited by establishing good childhood habits and continuing them lifelong, allowing people to be vital in old age, with few days of disability or morbidity. [Lifespan Link: Vitality, morbidity, and disability are explained in Chapter 20.]

The name for this extension of vitality into old age is compression of morbidity, which is the reduction (compression) of sickness before death. Ideally, a person is in good health for decades after age 65, and then, within a few days or months, experiences serious illnesses that lead to death. Years of frailty are avoided.

Morbidity has been compressed even as mortality is postponed. For instance, unlike 30 years ago, most people diagnosed today with cancer, diabetes, or a heart condition continue to be vital for decades. The World Health Organization and many experts recognize that disability is the result of person–environment interaction, so changing the environment limits disability (Phillipson, 2013). Cultures, schools, and technology can extend the optimal aging of the young–old, forestalling the morbidity of the oldest–old (Thompson et al., 2012).

The need for compression of morbidity is apparent with osteoporosis (fragile bones). Primary aging makes bones more porous as cells that build bone (osteo-blasts) are outnumbered by cells that reabsorb bone (osteoclasts) (Rachner et al., 2011). Osteoporosis is particularly common in underweight women with European ancestry, although men and people of other ethnic groups sometimes experience it.

The result of this chronic condition can be deadly, not just disabling. A fall that would have merely bruised a young person may result in a broken hip or a spine fracture, neither of which is lethal in itself but may potentially start a cascade of medical problems. Such a fall leads to death for 10 percent of osteoporosis sufferers within a year. According to The Center for Disease Control, a broken hip was “a leading cause of excess mortality among older adults” (MMWR, March 31, 2000). The problem was that half the people who broke their hips never walked again, and immobility causes many body systems to deteriorate.

Now let’s return to compression of morbidity. Note the 2000 date above. Now a more recent report: “In the 21st century, osteoporosis, a disease once considered an inevitable consequence of aging, is both diagnosable and treatable” (Black et al., 2012, p. 2051).

How was this compression of morbidity achieved? Early diagnosis via a bone density test (not available a few decades ago) can detect bone weakening long before the first fracture. Prevention can begin in middle age, or even earlier, with weight-bearing and muscle-strengthening exercise, and a lifelong diet with sufficient calcium and vitamin D. In addition, a dozen drug treatments (including HRT) reduce bone loss.

Because a focus on chronic conditions is relatively new and treatment of osteoporosis is newer yet, scientists do not know the consequences of ingesting preventive drugs over many years. The data suggest caution (Brown et al., 2012). As you know, drugs that prevent one problem may eventually cause another. [Lifespan Link: HRT (hormone replacement therapy) is discussed in Chapter 20.] Nonetheless, the 44 million people over age 50 in the United States who have weak bones need not experience the disabling breaks that those with osteoporosis once did. That is compression of morbidity.

Hearts and bones are only two examples. For almost every condition, morbidity can be compressed, although many people do not realize it. For instance, half the elderly population has arthritis, but few know that their stiffness and immobility can be reduced (Hootman et al., 2012). The same is true for diabetes, which often goes undiagnosed until it leads to other chronic problems of the heart, kidney, feet, eyes, and more (Caspersen et al., 2012).

Consider also breast cancer. That kills African American women at one and a half times the rate of European Americans, primarily because it is diagnosed too late, causing months of morbidity and then death rather than shorter morbidity and then recovery.

Gerontologists now agree that the goal is not simply to live a long life, but to live a long, healthy life; not to add years to life but to add life to years, via health habits, early treatment, and so on (Gremeaux et al., 2012). Demographers now calculate the number of healthy years. This has been done for each state of the United States (MMWR, July 19, 2013) (see Figure 23.7).

The U.S. data as well as the data from other nations show that there is no set age when people become frail. The correlation between sheer longevity and healthy longevity is positive; further compression of morbidity seems a realistic goal.