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WHY HUMANS AGE

(as of 2/05) It is possible we may live to be 1,000 years old. Here's the link to the BBC reporthttp://news.bbc.co.uk/2/hi/uk_news/4003063.stm . By the way, I see this guy regularly each year at the American Association of Aging meetings. As the photo shows, he's an unusual but brilliant character.

The American Association for the Advancement of Science is the largest scientific society in the world. A few years ago the society decided to do a series of public service announcements to help increase scientific literacy and interest in science. They produced a list of questions in which they thought people would be interested, and selected experts from the Association to answer these questions in 30-second sound bites. I was honored and challenged to answer the question "Why do humans get older?"

The short answer is this. There are two basic mechanisms by which we all age. The first is a wear-and-tear model, explained primarily by the free radical theory of aging, which simply states that we rust out like cars, our molecules increasingly oxidized from oxygen and other substances which generate free radicals. Eventually most of us succumb to age-associated diseases caused by accumulating damage to DNA, proteins, and membranes of which our cells are composed.

But it is the second mechanism which sets the current limit to human longevity of around 120 years. This limit is determined by genetic mechanisms. Our genetic clock consists of repeating sequences of DNA found on the end of each chromosome called telomeres, discovered in the 1980's. These ends get shorter every time a cell in our body divides, and when the ends get short enough, the cells lose the ability to divide further and eventually die.

Remarkably, in recent years, evidence has accumulated that we can control both of these processes, both slowing the free radical damage to reduce the risk of age-associated disease, and regrowing the telomeres so that we may be able to extend our lifespan indefinitely.

"Until now, the assumption that the maximum human life span is fixed has been justified...We may soon be able to extend the maximum human life span and postpone or prevent the onset of diseases associated with aging...An appropriate uncertainty regarding the human life span undermines any attempt to accurately predict health costs in the next century." Banks, DA, and Fossel, M., "Telomeres, cancer, and aging", JAMA 278: 1345-48 (1997)

June 2004 - Lecture Notes: Why do we age?

More on the free radical process

More on telomeres and maximum human lifespan

For information on extending human lifespan, click here.