Exceptional Human Longevity

What do the following groups of people have in common: residents of the island of Okinawa in Japan; Sardinians from Italy; and Seventh Day Adventists in Loma Linda, California? Though they may seem incredibly different, these populations all have life-spans that are considered by experts to be exceptionally long (in some cases, individuals can live to be over 100 years old) compared to most others around the world.

Studying the lives of humans around the world, as well as other species who have varying life spans, helps scientists understand the underlying mechanisms of aging: how it works on a cellular level, why it occurs at all, and what we can do to live healthier and longer lives.

What makes these groups so special and what can we learn from centenarians (people who live into their hundreds) about the aging process? Is it their genes, diets, other lifestyle factors, or is it simply luck – that is, have they been able to somehow dodge the diseases that others have fallen victim to along the way? The answer seems to be a little bit of all the above.

Researchers are very interested in learning from centenarians about what they’re doing right – or what they have done right for the preceding century. Studying the lives of humans around the world, as well as other species who have varying life spans, helps scientists understand the underlying mechanisms of aging: how it works on a cellular level, why it occurs at all, and what we can do to live healthier and longer lives.

Whether we’re talking about humans or yeast cells, aging refers to any time-related process that occurs during the life of the organism. This includes processes that have any kind of consequence – good, bad, or neutral – . Although it’s often used interchangeably with aging, the term “senescence” is actually a bit different: it refers only to the deteriorative changes that occur over time after a person or other animal is mature. These changes make the organism more vulnerable to disease, as well as decrease the likelihood of survival.

In multicellular organisms, like humans, senescence is thought to occur in species where the germ cell line is separate from the body cell lines and in those who give birth to separate (and smaller) offspring or, more specifically, in animals whose body cells differentiate and serve separate functions.

Humans, like all other animals with placentas, experience gradual senescence. This form progresses slowly but persistently after the animals is mature.

It is important to note that measuring life span in various populations can be tricky, since certain kinds of animals often fall victim to predators, infection, and other environmental factors that can lead to a high “accidental” death rate. . Still, despite these issues, senescence is thought to occur mainly as the result of the primary aging processes – that is, aging in the relative absence of disease or injury.(1)

The researchers estimated that over the course of human history, the odds of a woman living from birth to age 100 has risen from 1 in 20 million to 1 in 50 in countries like Japan and Sweden, which are considered to be “low mortality” nations.

Median life span, the age at which there are as many individuals with shorter life spans as there are individuals with longer life spans, and life expectancy are increasing in many populations across the globe. What factors are behind these increases? An important trend is that the number of premature deaths has decreased in recent years, which probably plays a bigger role in longevity than any significant changes to the aging process itself. (Figure 1). Over the last century, there has been a huge decrease in the infant death rate. This has been is due to a number of factors, such as improvements in sanitation, nutrition, and immunization.(1)

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Increase in average life span (block arrows), but not maximum life span, is the result of protection from premature death.

Median life span and life expectancy are therefore influenced by many factors and are probably not related to primary aging processes. However, in 2008, life expectancy at birth exceeded 80 years in 11 countries around the world. Even more astounding is that in the twentieth century, life expectancy doubled in some developed countries.(2) Although rising life expectancy at birth is not a universal phenomenon, the highest recorded average life expectancy is for Japan, where it continues to rise.(3) In fact, female life expectancy in Japan has risen steadily for the last 160 years at rate of almost 3 months/year. Figure 2 illustrates the average life expectancy in selected developed countries.

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Life expectancy at birth in 2008 in five developed countries. Source: U.S. Census Bureau, International Database, assessed on May 27, 2008.

Maximum life span has often been considered a fairly good index of the rate of aging of a population. The maximum life span for any species is usually inversely related to its rate of aging: in other words, the longer a species lives, the slower it tends to age. For example, rats, who have a maximum life span of about five years, are thought to age faster than dogs, whose maximum life span is about 20 years. Any factor that increases the maximum life span of a species is considered to have influenced primary aging processes.