How long are your telomeres?

A telomere shortening mechanism limits cells to a fixed number of divisions, and animal studies suggest that this is responsible for aging on the cellular level. In other words, it may be the mechanism that sets a limit on life spans.

Studies over the past two decades show that telomeres shorten with age. They have linked short telomeres with several diseases. Among other things, telomere length indicates how much "replicative potential" the host’s cells boast.

Telomeres prevent DNA from degrading like the plastic ends of shoelaces when replication takes place during cell division by protecting chromosome ends from fraying and sticking to one another. Without telomeres, replication of a gene would scramble genetic information to cause cancer, other diseases or death.

Each time a cell divides, the average person loses up to 200 telomere base pairs out of 8,000 or so that are present at birth, allowing each cell to divide 50 to 70 times. Each chromosome contains about 150 million total base pairs in its genetic code. With each cell division, telomeres get progressively shorter until the cells become senescent, die or sustain damage that can cause cancer.

One study showed that among people older than 60, those with shorter telomeres are three times more likely to die from heart disease and eight times more likely to die from infectious disease.

While telomere shortening has been linked to the aging process, it is not yet known whether shorter telomeres are just a sign of aging like gray hair or actually contribute to it.

Catherine Schaefer, an epidemiologist who directs the Kaiser Permanente Research Program on Genes, Environment and Health, measured the telomere length of more than 110,000 participants as part of an ongoing project exploring links between genetics and health. She reported that the 10 percent of people with the shortest telomeres had more than a 20 percent higher risk of dying during the three-year study period.

"The increased death risk is about the same as for people who drink 20 to 30 alcoholic beverages per week or smoke for 20 to 30 years," she said.

This study did not identify causes of death or the medical status of patients before they died. It did confirm that telomeres get shorter with age, but found that African-Americans tended to have longer telomeres in general than those of European, Asian or Latin ancestry.

Some results are not surprising: Heavy drinkers and smokers were more likely to have shorter telomeres.

Other results are puzzling: People with higher levels of education tended to have longer telomeres, but researchers found no connection between exercise and telomere length.

Higher body mass index is associated with longer telomeres. This counterintuitive result puzzled researchers because of the link between higher BMI and a host of health problems such as diabetes and heart disease, but other studies suggest that high BMI, short of obesity, is indicative of good health in the elderly.

These results and others like them are inconclusive as they relate to overall health, but definitely open the door to other studies that might eventually understand this relationship between body size and telomere length, and to sort out the relationship between genetic background, telomere length, health and longevity in general.

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Richard Brill is a professor of science at Honolulu Community College. Email questions and comments to brill@hawaii.edu.