Human longevity can be defined in three ways. The first and most common approach is average life expectancy for a particular age; the second is age-specific all-cause mortality rate (deaths/100 000 people/year), which is the inverse of longevity. A third but unconventional definition deals with the percentage of centenarians in a population, which indirectly reflects the longevity of the adult population. Note that the maximum life span (MLS) of humans appears to be fixed at approximately 120 years. Unlike life expectancy, which has increased substantially since ancient Rome, MLS has not changed over thousands of years. The following material reviews the longevity of various populations.
Factors Affecting Longevity
It is well established that environment is a key factor affecting the longevity of individuals and entire populations. This includes socioeconomic status (SES), the quality of medical care, educational facilities, and exposure to various diseases. Nutrition also has a critical role because malnutrition can cause susceptibility to infections and premature death (Samaras, 2006, 2007). While many populations suffer from food deprivation, many developing and developed populations experience excessive food intake, and obesity is now a worldwide health problem leading to reduced longevity (Elrick et al., 2002). In view of the increasing weight trend, the body mass index (BMI) has become an important guideline for predicting mortality and longevity. Generally, a BMI (weight/height2) of 19 to 23 kg/m2 with good nutrition predicts greater longevity.
Other factors that affect longevity are heredity; stress levels; traumatic events; regular physical activity; toxins in the environment, food, and water; and exposure to disease producing bacteria, viruses, and parasites. Although climate may play a role in longevity, long-living people are found in semitropical, cold, and temperate climates. The same is true for sea level and mountainous elevations. However, longevity appears to favor relatively small populations, such as Andorra ( ~80 000) and Sweden (~9 million ) as shown in Table 1.
Worldwide Variations In Life Expectancy
Life expectancy is the average age at death for a particular population group. Note that life expectancies are also determined for each age group, usually in 10-year increments.
Life expectancies are available for 225 populations ranging from China to the tiny sovereign states of Andorra and San Marino. As shown in Table 1, life expectancies at birth for males and females combined range from 33.23 years for Swaziland to 83.52 years for Andorra (Central Intelligence Agency, 2007).
Consistent with findings that a good environment and SES promote longevity, most of the longest living populations are found in highly developed populations with superior sanitation, education, and health care. The worst life expectancies are found in Africa with its lower economic development and very high rate of mortality from HIV/AIDS infection. The top ten populations in terms of descending life expectancy (83.52 to 80.59 years) are Andorra, Macao, Japan, Singapore, San Marino, Hong Kong, Sweden, Australia, Switzerland, and France. (Rankings shift from year to year but most of these states stay in the top ten or close to it.)
The low life expectancy of developing populations does not mean that elderly people are absent from developing populations. Since poor countries tend to have much higher infant death rates, this situation lowers the average life expectancy. In addition, early deaths of children and young adults due to malnutrition, trauma, and infections reduce the average life expectancy. However, if early death is avoided, adults often reach advanced ages (Walker, 1974; Samaras, 2007).
A common misconception in comparing today’s life expectancy to that of earlier times, such as the 1900s, is the belief that individuals can expect to live 25–30 years longer. However, if we look at the life expectancy of elderly people, the picture is quite different; e.g., 60year-old white males lived 6.6 years longer in 2004 vs 1900, and 80-year-olds lived 3 years longer.
Gender And Life Expectancy
Females commonly have greater longevity compared to men throughout their lives. Exceptions exist, such as in Martinique and Afghanistan. However, there is a substantial difference of less than 2 to more than 10 years in longevity between the sexes, depending on the populations involved. Generally, the greatest differences are found in developed populations. Several reasons for gender differences in longevity have been proposed, such as hormonal protection, more robust physiology, better health-care habits, and lower rates of high-risk activities. These factors no doubt have an impact, but animal and human research indicates that differences in body size may play a major role (Samaras, et al., 2002; Samaras, 2007). For example, one study reported that the average height for males in 21
European nations was 7.7% taller than females, and males had an 8.0% lower life expectancy (Samaras et al., 2003a). Another study by Miller, based on about 1700 men and women in Ohio, found that when men and women of the same height were compared, there was essentially no difference in average life span (Samaras, 1996). Rollo also found that when he compared male and female mice of the same body weight, the usual difference in average life span disappeared (Samaras, 2007). Brown-Borg and Bartke also reported that dwarf male mice lived substantially longer than normal-size female siblings (Samaras, 2007).
Centenarians
Centenarians are another population of interest. Gerontologists have studied people who live to be 100 or more years in an attempt to define the qualities or conditions that characterize centenarians as a special population. They have identified a variety of positive attributes, such as not smoking, small body size, diet, regular exercise, avoidance of stress, good environment, family connectedness, avoidance of worry, and a positive attitude toward life.
The greatest concentration of centenarians has been found in Okinawa, Japan, with 340–400/million, Bulgaria with 199/million, and Sardinia with 136/million. The Okinawans have been studied for many years and researchers have attributed their longevity to good nutrition and low caloric intake. Okinawan children in the recent past consumed about 40% fewer calories than children in mainland Japan (Samaras, 1996). Other factors were a simple life and life-long physical activity.
It should be noted that centenarians tend to be relatively short and light. This could be an artifact due to the trend toward greater height and body size during the last 150–200 years. In addition, people tend to shrink with age due to postural changes and compression of the discs in the spine, although shorter people shrink less than taller ones. However, the Okinawan male and female centenarians are quite short, averaging 148.3 cm and 138.6 cm respectively. After accounting for shrinkage and secular growth, these are still small people; for example, males equal to or exceeding 100 years were over 10 cm shorter than elderly men averaging 73 years of age (Chan et al., 1997). In addition, Paolisso et al. (1995) found Italian male centenarians averaged 162 cm and were 15 cm shorter than elderly men averaging 77.6 years. Note that shorter female centenarians normally outnumber taller males by a factor of three or four.
Longevity And Body Height
If we look at the countries with the greatest life expectancies, developed countries lead the world. Based on this fact, it would appear that the tallest and heaviest (and sometimes the fattest) populations in the world live the longest. However, a number of factors contradict this hypothesis. In fact, if the top six populations in terms of life expectancy are examined for height, it appears that most of them are relatively short. For example, the populations of Andorra (mostly Catalans and Spaniards), Macao (mostly Chinese), San Marino (similar to Italians), Singapore (mostly Chinese), Hong Kong (mostly Chinese), and Japan are shorter than the populations of northern Europe. In contrast, although Sweden ranks 7th from the top, other equally tall populations, such as Iceland, Norway, the Netherlands, Germany, and Denmark, average 29th from the top ranking (vs 3.3 for the top six populations). Note that the Dutch are the tallest people in the world and rank 28th in longevity.
The negative impact of excess weight on longevity is widely accepted in the medical community (Samaras, 2006, 2007). However, the role of height is controversial, and the following material will highlight conflicting findings on longevity based on height differences among several populations.
Studies Showing Taller People Have Greater Longevity
A review of life expectancy data shows that the tallest countries (and most developed) have on average the greatest longevity. Although not as great as the six top-ranking populations, Western and southern Europe, Australia, Canada, New Zealand, the UK, and the United States have substantially longer life expectancies compared to shorter nations in the Middle East, most of Asia, South America, and Africa. Approximately 40 studies found taller people have lower all-cause or cardiovascular disease mortality (CVD) (Samaras et al., 2003a). Since CVD is a major factor in reducing longevity, it indirectly supports the hypothesis that taller people live longer.
Waaler (1983) conducted a study of 176 574 deceased Norwegians and found that taller people had about a 15% lower mortality compared to shorter ones. However, at advanced ages, tall males experienced higher mortality. This study did not adjust findings for smoking, birth defects, accelerated growth, childhood illness, or SES. However, a more recent study from South Korea evaluated 386 627 middle-aged males and found all-cause mortality dropped 6% for a 10 cm increase in height when adjusted for SES and other factors (Song et al., 2003). However, no height trend was found for coronary heart disease (CHD).
Studies Showing Shorter People Have Greater Longevity
Data supporting the greater longevity of shorter people is at least as impressive as the findings showing taller people live longer. For example, a California study involved 1 million deaths of various ethnic groups and found tall people have over 100% higher all-cause mortality compared to short people, i.e., whites and blacks had over twice the all-cause mortality of the Chinese and Japanese. Latinos and South Asians, who were slightly taller than the Chinese, had similar mortality rates (Samaras, 2007). A similar pattern was found for CHD.
Another study involving 1.3 million Spanish military recruits tracked them for 70 years into their 80s and 90s and found a strong negative correlation (r = –0.58) between height and survival age (Samaras, 2007). The findings were based on measured conscription heights and deaths from national census data.
Insurance studies involving 4.5 million men and women reported that all-cause mortality increased with increasing height for middle-aged women and men ( ~30% for the tallest men) (Samaras et al., 2003a). In addition, several longevity studies of athletes in Finland and the United States revealed that shorter athletes lived longer than taller ones. The loss of life with increasing height averaged about 0.52 year/cm (Samaras, 2007).
Shorter people throughout the world have been found to have superior longevity or reduced chronic disease. These findings are summarized in Figure 1. Note that the lower left hand rectangle only lists four sample populations for low CHD. Many others exist, including Solomon Islanders, Congo Pygmies, Vietnamese, Papua New Guinea inhabitants, the Chinese and the Japanese. Based on a review of 300 studies by Gunnell et al., shorter people also have lower cancer mortality (Samaras, 2007).
Potential Confounders In Height Studies
There are a number of explanations for the conflicts between studies showing positive or negative relations between longevity and body height. As mentioned before, longevity is a function of many factors and conditions, and height is only one factor, probably representing roughly 10–20% of the total impact. For example, SES for all major phases of life has an important bearing on longevity independent of height. In addition, since people in higher SES are generally taller, the benefits due to SES can offset the negative effects of increased body height. Another confounder is BMI because taller people tend to have higher BMIs when of similar proportions as shorter people (Samaras, 2007). However, most epidemiological studies use the same BMI to evaluate the mortality of tall and short people. This process results in comparing taller, leaner people against shorter, stockier people. Since leaner people tend to have a lower mortality, this bias can favor taller people (Samaras, 2007).
Other confounders involve prenatal and postnatal care and early growth patterns. In recent years, it has been found that catch up or accelerated growth in height and weight promotes obesity and chronic disease in adulthood (Samaras et al., 2003b; Samaras, 2007). Since low-birth weight children generally become shorter adults compared to their normal-weight peers, their increased mortality is interpreted to result from their shorter height or lower SES rather than to accelerated growth and related health problems caused by excess weight (Samaras, 2007). Another potential problem is congenital or early childhood illness that results in shorter adult height and poorer health.
Animal Findings
There is strong evidence that larger animal species live longer than small ones. The obvious example includes a comparison between a mouse and an elephant. This advantage is mainly due to lower metabolic rate and evolutionary changes that resulted in greater cell replication potential and improved free radical defenses and DNA repair mechanisms. However, since the 1930s, robust findings indicate that within a species, smaller size promotes greater longevity. Rollo (Samaras, 1996, 2007) evaluated hundreds of longevity studies involving mice and rats and found a highly significant and substantial inverse relationship between body size and longevity. In addition, Miller and Austad (2006) reported that small dogs had greater longevity than medium and large ones. The most recent study on dogs found that there was a substantial negative correlation between height and survival (Greer et al., 2007). For a wide height range of 15–94 cm, they found r = –0.603, p < 0.05. For a weight range of 0.9–89 kg, r = –0.679, p < 0.05.