Large study examines association between protective caps at end of chromosomes and health.By Tina Hesman Saey Web edition: November 11, 2012 Article from sciencenews.org
SAN FRANCISCO — Nearly gnawed-off telomeres — the protective caps on the ends of chromosomes — may portend a higher risk of death, a new study suggests.
Telomeres prevent a chromosome’s DNA from being eaten away. Previous studies have shown that telomeres shorten with age and linked short telomeres with several diseases. What no one has yet been able to say is if truncated telomeres cause health problems or are a side effect of aging and poor health.
To find out, researchers at Kaiser Permanente and the University of California, San Francisco measured telomere length in 110,266 people in northern California. The participants are part of an ongoing project that explores links between genetics and health. This study is the largest ever to examine telomeres’ role in health.
The 10 percent of people with the shortest telomeres had a more than 20 percent higher risk of dying than people with longer telomeres, Catherine Schaefer, an epidemiologist who directs the Kaiser Permanente Research Program on Genes, Environment and Health, reported November 8 at the annual meeting of the American Society of Human Genetics. “It seems as though once your telomeres get critically short, your risk of dying goes up,” she said. 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. “It’s a modest increase, but it’s not nothing.”
The researchers don’t yet know the health status of the people who died.
Telomeres do get shorter with age, the study confirms, but men older than 75 and women over age 80 tended to have longer telomeres than their slightly younger counterparts. That result does not mean that telomeres start to grow in length once people reach a certain age, Schaefer said. Rather, the finding probably means that people with shorter telomeres died before they reached those ripe old ages and the survivors are those that carry longer telomeres.
African-Americans tended to have longer telomeres than European-Americans, Latinos or Asians, the researchers found. The reason for that difference is not clear. As expected, people who smoked or drank heavily were more likely to have shorter telomeres, and higher levels of education were associated with longer telomeres. Other studies have linked exercise with longer telomeres, but Schaefer and her colleagues found no such association.
One of the study’s findings is rather puzzling, said Dan Eisenberg, an anthropologist at the University of Washington in Seattle who studies telomeres’ link to health, but who was not involved in the Kaiser Permanente study. Higher body mass index, or BMI, was associated with longer telomeres. The discovery is counterintuitive, Eisenberg said, because higher BMIs —those associated with being overweight or obese — are linked to a variety of health problems including diabetes and heart disease. Eisenberg said he would have expected telomeres in people with higher BMIs to be shorter.
Schaefer agrees that the BMI link is a provocative finding. “We know that high BMI is not healthy,” she said, but more work will be needed to understand the relationship between body size and telomere length.