Are telomeres the most inaccurate biological clock?
Technological advances allow researchers to quantify the finest parameters of the human body, which significantly deepens our knowledge about health, diseases and aging. However, as the data obtained by researchers working under the guidance of Dr. Dana A. Glei from Georgetown University showed, when predicting a person's death, such simple parameters as age and the ability to climb stairs or walk short distances are much more powerful prognostic factors than popular biomarkers.
Several decades ago, scientists established that telomeres, which perform a protective function, act as a "molecular clock" for human cells. Each time a cell divides, the telomeres shorten to reach a critical length, after which the cells lose their ability to divide. Telomere length is usually estimated in leukocytes and there is evidence to support the existence of an association between shorter leukocyte telomeres and morbidity, aging and mortality. This aroused great interest in the possibility of using this biomarker to predict mortality.
According to the authors of an article published in the journal PLOS ONE (Glei et al., Predicting Survival from Telomere Length Versus Conventional Predictors: A Multinational Population-based Cohort Study), scientific data on the length of telomeres were sensational in nature and in some cases were exaggerated by the press and companies that earned on the development and sale of products, the promises associated with them far exceed the real possibilities. This is what prompted them to conduct this study dedicated to the study of the real ability of telomere length to predict mortality better than well-known prognostic factors, the evaluation of most of which does not require invasive interventions and large financial costs.
As part of the work, the authors summarized data collected in the USA, Costa Rica and Taiwan during three major studies on aging. They analyzed mortality rates for 5 years after measuring telomere length in elderly people: aged 60 years and older in the United States, 61 years and older in Costa Rica and 53 and older in Taiwan.
For each country, the authors compared telomere length indicators with a wide range of widely used prognostic factors of mortality. These included basic demographic indicators (age, gender), social factors (family status, education level and social integration), attitude to health (smoking, sports), self-assessment of health (general health, physical mobility, difficulties in performing daily household tasks, the presence of diabetes and cancer, the number of hospitalizations over the past year), the results of tests for cognitive abilities and a number of biomarkers, including blood pressure, cholesterol levels, the concentration of glycosylated hemoglobin in the blood (used to monitor diabetes mellitus), body mass index, the level of C-reactive protein (produced by the liver in response to inflammation), as well as the level of serum creatinine, which is an indicator of kidney function.
The results of the statistical analysis showed that, despite the existence of an association between telomere length and survival for all three countries, the power of this indicator in predicting 5-year survival is lower than the power of many other indicators. Banal as it may seem, but for residents of all three countries, the chronological age turned out to be the best predictive factor of mortality, close to which the self-assessment of the level of mobility was located.
There are strong correlations between telomere length and gender, as well as a person's age. Therefore, the researchers decided to clarify how well this parameter allows predicting mortality when adjusting for these two demographic indicators. After the amendments were made, the rating of telomeres in the list of prognostic factors of mortality dropped even lower. For Costa Rica, they were in 15th place, and for Taiwan and the United States - in 17th place out of 20 possible.
The authors note that there are a number of limitations for the results obtained. During the study, telomere length was measured in leukocytes, some types of which are characterized by longer telomeres. In seriously ill patients, the ratio of leukocyte types may shift in such a way that during the analysis, the average value of the telomere length may shift in a larger direction.
Perhaps telomere length, reflecting the gradual aging process of cells, may be a more powerful prognostic factor for long-term than for short-term mortality. It has also been suggested that it may be an indicator of healthy aging, as scientists are receiving more and more evidence in favor of the fact that short telomeres are associated with cardiovascular diseases. However, more research is needed to clarify the relationship between telomere length and other diseases, such as cancer. In addition, a working prognostic factor may be a change in the length of telomeres, and not a measurement made at one time.
In general, the researchers concluded that telomere length may eventually help researchers understand the mechanisms of aging, but it is a much less powerful predictor for assessing the likelihood of death within 5 years than other basic parameters, the measurement of which is much easier and cheaper, since it does not require obtaining a blood sample and DNA isolation..
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of Princeton University: Age and Mobility Predict Death Better Than One's 'Molecular Clock'.
08.04.2016