Posted on Apr 13, 2016, 6 a.m.
DNA may not be the best indicator of how long we'll live, after all. Instead, simpler measures may give more accurate predictions.
Researchers discovered years ago that telomeres (the protective caps on the ends of chromosomes) act as a 'molecular clock' in human cells. Telomere length has been touted as a strong predictor of longevity, since DNA sequences shrink with age. Shorter telomeres have been connected to disease, aging and mortality. A recent study shows that this method of prediction may in fact be largely ineffective. Researchers from Princeton University; Stanford University; University of Washington; Georgetown University; the University of California, Berkeley; and the Universidad de Costa Rica compared a wide set of predictors of death,such as age, smoking habits, and mobility, with the length of their telomeres. The data used was from data from three countries; United States, Costa Rica and Taiwan. Specifically, the data was obtained from the U.S. National Health and Nutrition Examination Survey, the Costa Rican Study on Longevity and Healthy Aging and the Taiwan Social Environment and Biomarkers of Aging Study.
The researchers analyzed deaths that occurred within five years after telomere length was measured in older individuals: age 60 and above for the United States; age 61 and above for Costa Rica; and age 53 and above for Taiwan. They tested the length of the telomeres against a broad set of well-known predictors of death, including age, sex, social factors, smoking, exercise, physical mobility, activities of daily living limitations, history of diabetes and cancer, and the amount of hospital admissions over the past year. Additionally, they administered a cognitive test, and measured several biomarkers, including blood pressure, cholesterol, glycosylated hemoglobin (which is used to monitor diabetes), body mass index, C-reactive protein (produced in the liver in response to inflammation) and serum creatinine, which is indicative of kidney function.
They found that while telomere length was associated with survival, it ranked lower than many of the other predictors, in regards to it's ability to dilenate between those who died and those who lived over the five years. Age was unsurprisingly the best predictive measure, with self-reported mobility a close second. When the researchers controlled for age and sex, they found telomere length ranked close to the bottom. 13 other indicators were shown to more strongly predict mortality then telomere length in each of the three of the countries studied. The researchers conclude that, although telomere length may at some point in the future help scientists better comprehend aging, it is not as powerful a predictor for death over a five-year timespan as other simple, more easily obtained measures. "It is much easier and less expensive to ask someone's age than to collect blood, extract DNA and measure telomere length," said Glei. Upon evaluating the data, they found that using telomere length to predict death was only slightly better than a "coin toss". Chronological age was largely the single most accurate predictor of death in all three countries.
"Scientific evidence on telomere length has been sensationalized and, in some cases, exaggerated by the media and by companies that have capitalized on the research to market products that may promise more than they can deliver," said lead author Dana A. Glei, a senior research investigator at Georgetown University's Center for Population and Health. "This is what fueled our research. We wanted to determine whether telomere length could predict mortality better than other well-established predictors of survival, most of which are less invasive and much less costly to measure."
While these elemental measures may not be able to identify the root causes of disease, being able to accurately predict mortality can be very beneficial to physicians who are advising their patients about the risks and benefits of a potential treatment. For prognostic purposes, physicians often rely on conventional predictors, such as lage, sex and physical function. These findings provide no evidence to suggest that physicians should begin testing telomere length in order to improve their survival prognoses. "On the internet, they sell test-your-own-telomere length kits and supplements that are touted to help people maintain their telomeres. We caution buyers to beware," stated Glei.
Dana A. Glei, Noreen Goldman, Rosa Ana Risques, David H. Rehkopf, William H. Dow, Luis Rosero-Bixby, Maxine Weinstein. Predicting Survival from Telomere Length versus Conventional Predictors: A Multinational Population-Based Cohort Study. PLOS ONE, 2016; 11 (4): e0152486 DOI: 10.1371/journal.pone.0152486