Are telomeres really the key to living longer, youthful lives?
Are longer telomeres key to longevity, or should we be looking to other ways
ISLAMABAD, (Online) - Telomeres — the “caps” on the end of chromosomes that protect the DNA from damage — have been associated with greater longevity. In theory, longer telomeres should allow a cell to divide more times and therefore live longer. However, a new study has suggested that longer telomeres could increase a person’s risk of chronic health conditions. So are longer telomeres key to longevity, or should we be looking to other ways of living longer, healthier lives?
What do we really know about how telomere length relates to aging processes?
Increasing age is the greatest risk factor for many health conditions. However, some people seem to age better than others, enjoying an active, healthy existence long into old age. So how do they do this? Some credit a healthy lifestyle, others luck, and others genetics.
One theory about aging well lies in our chromosomes or, more specifically, our telomeres — protective lengths of repetitive deoxyribonucleic acid (DNA) and protein found at the end of each chromosome.
Inside every cell in the human body there are 23 pairs of chromosomes. Each chromosome is made up of DNA wound around proteins. That DNA contains genes — inherited instructions for all the cell’s functions.
Telomeres are found at the terminal region of each chromosome and do not contain genes. Each time a cell divides, the chromosomes replicate and the telomeres shorten. This allows the cell to divide without losing vital genes. Eventually, the telomeres are too short for the cell to divide again and the cell becomes senescent or dies.
Shorter telomeres have been associated with increased disease incidence and decreased survival times. Senescent cells no longer divide, but remain active and have been implicated in many diseases of agingTrusted Source, such as osteoarthritis, atherosclerosis, and cancer.
Longer telomeres should mean that cells can divide more often before entering senescence or dying, therefore increasing longevity. Animal studies have shown that telomeres shorten faster in short-lived animals than in longer-lived ones.
A study in mice bred to have hyper-long telomeres found that they were lean, had low cholesterol and LDL levels, and improved glucose and insulin tolerance. They also lived longer and had a lower incidence of cancer than regular mice.
So longer telomeres mean longer, healthier lives. Or do they?
Telomeres and biological age
Telomeres are maintained by the enzyme telomerase. This adds to the telomeres, preventing them from shortening as rapidly, thereby allowing the cells to live for longer. A good thing, perhaps, until we learn that cancer cells have increased amounts of telomerase, which allows them to continue dividing.
Sebnem Unluisler, genetic engineer and chief longevity officer at the London Regenerative Institute in the United Kingdom, told Medical News
Today:
“Studies have demonstrated a correlation between telomere length and biological age. Generally, shorter telomeres are associated with advanced chronological age and increased susceptibility to age-related diseases. Moreover, individuals with certain genetic variations or lifestyle factors that accelerate telomere shortening tend to exhibit a more rapid aging phenotype.”
Telomere length has been likened to a “biological clock,” with shorter telomeres indicative of greater biological age. Several lifestyle factors have been associated with shorter telomeres. One is a lack of physical activity.
In one study, sedentary women were found to have telomeres that indicated they were biologically 8 years older than women of the same chronological age who exercised more.
Tobacco smoking increases the risk of many diseases, and it also accelerates the shortening of telomeres. A study found that telomere shortening was enhanced in the circulating white blood cells of smokers, increasing the rate of biological aging.
Getting insufficient sleep can also influence telomere length, shortening telomeres even in childhood, which may lead to impaired health.
All of these are linked to inflammation, which is associated not only with telomere shortening, but with a number of diseases that are more common in later years.
Other factors that decrease telomere length are stress, depression, and certain gene mutations, such as that which leads to progeria — a rare condition in which children age extremely rapidly and rarely live past their teenage years.
Maintaining telomere length via diet, exercise
“Recent studies have suggested that telomere length alone may not be a reliable predictor of lifespan or aging. For example, some individuals with shorter telomeres have been found to live longer than those with longer telomeres. Other factors, such as lifestyle, environment, genetics, and stress also play a role in aging and disease.”
– Dr. Joshua Berkowitz, medical director at IV Boost UK
Shorter telomeres may be associated with shorter lifespans and more rapid biological aging, but are longer telomeres therefore associated with longer lifespans and healthier aging? The evidence is not conclusive.
Many lifestyle factors that are associated with better health are also associated with telomere length.
A diet rich in legumes, wholegrain, and fresh fruit and vegetables, such as the Mediterranean diet, is positively associated with telomere length in several studies. The positive effects of the Mediterranean diet on telomeres may be due to its antioxidant and anti-inflammatory properties.
Physical activity is advisable for general health, but the evidence for the effect of physical activity on telomere length is not clear-cut — although exercise is thought to be beneficial, the optimal exercise dose is unclear.
One study found that moderate exercise helps maintain telomere length, but the benefits decrease with excessive exercise; others found an effect only in people taking extreme amounts of exercise, such as ultra-marathon runners.
Other studies have shown that getting enough sleep, never having smoked tobacco, and avoiding stress may help preserve telomere length.
Challenging notions about telomeres
“While previous research has suggested that longer telomeres may be associated with longevity, most of this research has been done in cells, and it is not yet clear whether longer telomeres in humans are a cause or a consequence of healthy aging.”
— Sebnem Unluisler
One study even found that telomeres at both extremes — much longer or shorter than average — were associated with susceptibility to diseases. Short telomeres were linked to organ failure, and long ones to a variety of cancers.
Now, a new study has shown that longer telomeres may not be the key to healthy aging. It suggests, instead, that long telomeres allow cells with age-related mutations to live longer, increasing the likelihood of tumors and other chronic health conditions.
The study, which looked at people with a mutation (POT1) that causes longer telomeres, found that, while some showed signs of youthfulness, such as no gray hair in their 70s, those with the mutation had a higher incidence of benign and cancerous tumors, as well as the age-related blood condition clonal hematopoiesis, which increases the risk of several cancers, than those without.
One of the authors, Dr. Mary Armanios, professor of oncology at the Johns Hopkins Kimmel Cancer Center, and professor of genetic medicine, molecular biology and genetics, and pathology at the Johns Hopkins University School of Medicine, suggests an explanation.
According to her, “[c]ells with very long telomeres accumulate mutations and appear to promote tumors and other types of growths that would otherwise be put in check by normal telomere shortening processes.”
Sebnem Unluisler commented that “[t]his study suggests that there may not be a simple relationship between telomere length and aging.”
”While longer telomeres may be associated with increased cancer risk, they may also be associated with decreased risk of other age-related diseases and improved overall health,” she noted.
