infoaging guides BIOLOGY OF AGING BIOMARKERS OF AGING An introduction to aging science brought to you by the American Federation for Aging Research WHAT ARE BIOMARKERS Current research is looking OF AGING? closely into the process of Aging is a process that can affect aging and seeking ways to almost all the systems in the body. With increasing age, physically slow it down. and mentally healthy adults gradu- ally become less fit and more vulnerable to illness and death. However, these changes happen at different rates in different people. Scientists are looking for a more complete understanding of the mechanisms of aging, to answer questions about the biological processes that account for an inevitable decline in physical vitality. For example, is there an underlying process that accounts for grey hair, wrinkled skin, decreased muscle strength, increased susceptibility to disease, and all the other consequences of aging? Currently, the only way to test CRITERIA FOR BIOMARKERS interventions that are aimed at In other words, is aging a single OF AGING extending life is to conduct studies process that affects many of the that follow subjects to the end of While there are several candidates body’s systems, or are separate their lives. This can take an imprac- for biomarkers of aging, none have processes going on within each tically long time. What’s needed are so far proven a true measure of system? For example, one theory biomarkers of the aging process the underlying aging process. A suggests that oxidative damage that could help determine a true biomarker of aging must meet may be an underlying cause of person’s life expectancy, making certain criteria in order to be both many aspects of aging. Over the it unnecessary to wait many years accurate and useful: course of a lifetime, free radicals for the results of studies. in the body damage tissue in vari- • It must predict a person’s ous organs, which eventually leads Ideally, there would be a set of physiological, cognitive, and to aging. This would be a single these biomarkers that would physical function in an age- process model. identify biological age. These related way. In other words, it could be used to test whether a must predict the future onset Current research is looking closely behavior (such as exercise), drug, of age-related conditions and into the process of aging and or dietary additive slowed down diseases, and do so indepen- seeking ways to slow it down. In the aging process. dently of chronological age. order to test new interventions (i.e., drugs, vitamins, etc.), there If a set of biomarkers of aging • It must be testable and not has to be a way to determine if the were identified, it would also have harmful to test subjects. For intervention is having an impact on the effect of demonstrating that example, it could be a blood the underlying process of aging— there actually is an underlying test or an imaging technique. It not just whether it has an effect mechanism of aging that coordi- must also be technically simple on one of the body’s systems, nates changes across the body’s so that most clinical labora- such as affecting blood pressure systems. tories could perform the test or cholesterol levels, but whether accurately and reproducibly it slows down the actual aging without the need for special- process. ized equipment or techniques. 2 | Infoaging Guide to Biomarkers of Aging • It should work in laboratory takes place at a measurable contributed to the body of knowl- animals as well as humans, overall rate. The goal for these edge on aging, no biomarkers since preliminary testing is scientists is to find the biomarkers were successfully identified and always done in non-human and convince the doubters. validated. Since then, obtaining subjects. funding for biomarkers research HURDLES TO IDENTIFYING has become more difficult. Simply put, biomarkers need to BIOMARKERS OF AGING be simple and inexpensive to use. TARGETS FOR BIOMARKERS They should cause little or no pain Although scientists have been OF AGING and stress. And they must measure interested in finding biomarkers of aging accurately. aging since the National Institute Studies on biomarkers of aging on Aging organized its first confer- have looked for changes in cells, CRITICS OF BIOMARKERS ence on the subject in 1981, none hormones, genes, and even OF AGING have yet been identified. One dif- behaviors to find a predictor of ficulty has to do with the overlap the rate of aging. Not everyone is convinced that between aging and disease. Both biomarkers of aging actually exist. the aging process and diseases One target that has been looked Some critics doubt that there is can cause changes in the body, at is the central nervous system an underlying aging process at all. which affect lifespan. (consisting of the brain and spinal Therefore, there can be no marker cord). Computerized tomography for it. It has been difficult, however, to (CT) scans can be used to look separate out the aging process for changes in the brain that may Some scientists believe that as from conditions that precede the serve as biomarkers of aging. For people age, deleterious physi- onset of disease, as growing older example, the brain shrinks with ological processes can occur that predisposes a person to many age. This does not mean that may lead to cancer, heart disease, illnesses. Arguably, markers in the brain cells necessarily die, but dementia, or other diseases. These blood, such as cholesterol and rather that they become smaller in processes can overlap, but there C-reactive protein levels, both size and volume. Some research is no single, underlying biological measure some aspects of aging has been done to find out if brain process driving them all. and predict the onset of certain shrinkage in certain areas may Critics also argue that aging age-related diseases. underlie the changes in function doesn’t occur at a single rate, that occur with age. So far, brain Another obstacle lies in the fact function and age have proved and therefore the rate of aging that some age-related changes can’t be measured. Different body too complex to produce reliable cause no harm, while others biomarkers. functions can change at different do—and medical science doesn’t rates over time. A person may lose always know which is which. This Age at menopause has been muscle strength faster than his makes it more difficult to pinpoint suggested as a possible biomarker or her eyesight deteriorates. And exactly what to look for. of aging in women. One study there can be different reasons for showed that women who had early the deterioration. For example, a From 1988 to 1998, the National menopause (before age 44) had person may lose muscle strength Institute on Aging sponsored a shorter lifespans than women who faster because he or she never 10-year initiative encouraging experienced menopause at ages had much strength to begin with. research into biomarkers of aging. 50 to 54. This suggests that ovar- Although researchers explored ian function is related to the overall Despite these criticisms, many many interesting candidates researchers still believe aging aging process, but the mechanistic for possible biomarkers and links for this require further study. Infoaging Guide to Biomarkers of Aging | 3 is an important tool in the body’s to age-related diseases, at least Other possible biomarker targets ability to prevent cancerous tumors in animals. By removing most of include cell replication rate and from developing. The older a these cells from several organs immunological markers. person becomes, the more senes- (body fat, eye, and skeletal tissue) cent cells he or she accumulates. of lab mice, the investigators were THE FUTURE OF BIOMARKERS Several markers of senescence in able to significantly delay the OF AGING RESEARCH humans have been suggested as onset these diseases, or stop their At the level of cells, a potential biomarkers of aging. progression if they had already become established. biomarker of aging may be the On November 10, 2011, presence of senescence. researchers at the Mayo Clinic The study suggests what may Senescence is a condition in published a study in the journal prove fruitful areas for future which old or damaged cells remain Nature showing that an accumula- researchers to explore in the search alive but cease to reproduce. This tion of senescent cells may lead for true biomarkers of aging. American Federation for Aging Research (AFAR) Websites: 55 West 39th Street, 16th Floor www.afar.org New York, NY 10018 www.afar.org/infoaging Phone: (212) 703-9977 Facebook and Twitter: Toll-free: (888) 582-2327 AFARorg Fax: (212) 997-0330 Email: [email protected] © 2016 American Federation of Aging Research. All rights reserved. 4 | Infoaging Guide to Biomarkers of Aging.