TOP
The number of centenarians, people who've reached their hundredth birthday, has been increasing. The UK had more than 14,000 centenarians in 2015 compared to less than 8,000 in 2002.1 In 50 years, the figure is projected to exceed 400,000. The U.S. currently has around 53,000 centenarians.2 Why do some people live longer than others, and how long can a human being really live?
It is generally accepted that genetic, environmental and behavioural factors contribute to lifespan. Studies of identical twins are commonly used to research the effect of genetic factors compared to environmental and behavioural ones. This is particularly useful in studying twins who were separated at birth, meaning that they share the same genetic makeup but have different environmental influences. Such studies show that differences in genetic makeup can explain perhaps 20%-30% of the differences in longevity from person to person.
However, the influence of genetic factors has been demonstrated by the New England Centenarian Study - one of the world’s largest studies - which includes an international survey of centenarians and their siblings.3 According to the study’s findings, siblings of centenarians have a much higher chance of reaching age 100 than the general population. It also shows some environmental effects; those of extreme age tend not to be obese, rarely have a substantial smoking history and handle stress better than most people.
In addition to genetics, the effects of epigenetics on the aging process also have to be considered. Although our DNA varies from individual to individual, it does not change throughout life and it is epigenetics that determines when the genes are expressed (turned on or turned off). When we are young, we express genes that help us grow and develop. As we age, we express different genes, such as those that cause inflammation, and fewer genes that result in cell repair. The correlation between age and epigenetic status is widely accepted. However, whether aging causes us to express different genes when we are older or whether our epigenetic markers cause us to express different genes that lead to aging is open to debate.
In addition to the factors that lead to aging and longevity is the question of whether there is a limit to the potential human lifespan. Life expectancy has been rising for many years. One school of thought suggests this demonstrates the potential for increasing life expectancy in the future. Supporting this theory is the potential for cures of major diseases, such as cancer, and for bodily tissues and organs to be regenerated, which leads to the conclusion that there may be no limit on possible lifespan. The alternative view is that human lifespan has a fixed frontier and that even if we eliminated all cancer, heart disease and diabetes, we could expect to live no longer than perhaps age 120.
Clearly, future projections of mortality have a major effect on pricing and reserving for annuity and protection portfolios. The differing schools of thought on why we age and how long we can live clearly make this a challenging task.
