Researchers are finding that your mental patterns could be harming your telomeres — essential parts of the cell’s DNA — and affecting your life and health. Nobel-winning scientist Elizabeth Blackburn and health psychologist Elissa Epel explain.

How can one person bask in the sunshine of good health, while another person looks old before her time? Humans have been asking this question for millennia, and recently, it’s becoming clearer and clearer to scientists that the differences between people’s rates of aging lie in the complex interactions among genes, social relationships, environments and lifestyles. Even though you are born with a particular set of genes, the way you live can influence how they express themselves. Some lifestyle factors may even turn genes on or shut them off.

Deep within the genetic heart of all our cells are telomeres, or repeating segments of noncoding DNA that live at the ends of the chromosomes. They form caps at the ends of the chromosomes and keep the genetic material from unraveling. Shortening with each cell division, they help determine how fast a cell ages. When they become too short, the cell stops dividing altogether. This isn’t the only reason a cell can become senescent — there are other stresses on cells we don’t yet understand very well — but short telomeres are one of the major reasons human cells grow old. We’ve devoted most of our careers to studying telomeres, and one extraordinary discovery from our labs (and seen at other labs) is that telomeres can actually lengthen.

What this means: aging is a dynamic process that could possibly be accelerated or slowed — and, in some aspects, even reversed. To an extent, it has surprised us and the rest of the scientific community that telomeres do not simply carry out the commands issued by your genetic code. Your telomeres are listening to you. The foods you eat, your response to challenges, the amount of exercise you get, and many other factors appear to influence your telomeres and can prevent premature aging at the cellular level. One of the keys to enjoying good health is simply doing your part to foster healthy cell renewal.

People who score high on measures of cynical hostility have shorter telomeres.

Scientists have learned that several thought patterns appear to be unhealthy for telomeres, and one of them is cynical hostility. Cynical hostility is defined by high anger and frequent thoughts that other people cannot be trusted. Someone with hostility doesn’t just think, “I hate to stand in long lines at the grocery store”; they think, “That other shopper deliberately sped up and beat me to my rightful position in the line!” — and then seethe. People who score high on measures of cynical hostility tend to get more cardiovascular disease, metabolic disease and often die at younger ages. They also have shorter telomeres. In a study of British civil servants, men who scored high on measures of cynical hostility had shorter telomeres than men whose hostility scores were low. The most hostile men were 30 percent more likely to have a combination of short telomeres and high telomerase (an enzyme in cells that helps keep telomeres in good shape) — a profile that seems to reflect the unsuccessful attempts of telomerase to protect telomeres when they are too short.

These men had the opposite of a healthy response to stress. Ideally, your body responds to stress with a spike in cortisol and blood pressure, followed by a quick return to normal levels. Instead, when these men were exposed to stress, their diastolic blood pressure and cortisol levels were blunted, a sign their stress response was, basically, broken from overuse. Their systolic blood pressure increased, but instead of returning to normal levels, it stayed elevated for a long time afterward. The hostile men also had fewer social connections and less optimism. In terms of their physical and psychosocial health, they were highly vulnerable to an early disease-span, the years in a person’s life marked by the diseases of aging, which include cardiovascular disease, arthritis, a weakened immune system and more. Women tend to have lower hostility, and it’s less related to heart disease for them, but there are other psychological culprits affecting women’s health, such as depression.

When you ruminate, stress sticks around in the body long after the reason for the stress is over.

Pessimism is the second thought pattern that has been shown to have negative effects on telomeres. When our research team conducted a study on pessimism and telomere length, we found that people who scored high on a pessimism inventory had shorter telomeres. This was a small study of about 35 women, but similar results have been found in other studies, including a study of over 1,000 men. It also fits with a large body of evidence that pessimism is a risk factor for poor health. When pessimists develop an aging-related illness, like cancer or heart disease, the illness tends to progress faster. Like cynically hostile people — and people with short telomeres, in general — they tend to die earlier.

Rumination — the act of rehashing problems over and over — is the third destructive thought pattern. How do you tell rumination from harmless reflection? Reflection is the natural, introspective analysis about why things happen a certain way. It may cause you some healthy discomfort, but rumination feels awful. And rumination never leads to a solution, only to more ruminating.

When you ruminate, stress sticks around in the body long after the reason for the stress is over, in the form of prolonged high blood pressure, elevated heart rate, and higher levels of cortisol. Your vagus nerve, which helps you feel calm and keeps your heart and digestive system steady, withdraws its activity — and remains withdrawn long after the stressor is over. In a study, we examined daily stress responses in healthy women who were family caregivers. The more the women ruminated after a stressful event, the lower the telomerase in their aging CD8 cells (the crucial immune cells that send out proinflammatory signals when they are damaged). People who ruminate experience more depression and anxiety, which are, in turn, associated with shorter telomeres.

The fourth thought pattern is thought suppression, the attempt to push away unwanted thoughts and feelings. The late Daniel Wegener, a Harvard social psychologist, once came across this line from the great Russian writer Leo Tolstoy: “Try to pose for yourself this task: not to think of a polar bear, and you will see that the cursed thing will come to mind every minute.” Wegener put this idea to the test through a series of experiments and identified a phenomenon he called ironic error, meaning that the more forcefully you push your thoughts away, the louder they call out for your attention.

Ironic error may also be harmful to telomeres. If we try to manage stressful thoughts by sinking the bad thoughts into the deepest waters of our subconscious, it can backfire. The chronically stressed brain’s resources are already taxed — we call this cognitive load — making it even harder to successfully suppress thoughts. Instead of less stress, we get more. In a small study, greater avoidance of negative feelings and thoughts was associated with shorter telomeres. Avoidance alone is probably not enough to harm telomeres, but it can lead to chronic stress arousal and depression, both of which may shorten your telomeres.

Thought awareness can promote stress resilience. With time, you learn to encounter ruminations and say, “That’s just a thought.”

The final thought pattern is mind wandering. Harvard psychologists Matthew Killingsworth (TED Talk: Want to be happier? Stay in the moment) and Daniel Gilbert (TED Talk: The surprising science of happiness) used a “track your happiness” iPhone app to ask thousands of people questions about what activity they are engaged in, what their minds are doing, and how happy they are. Killingsworth and Gilbert discovered we spend half of the day thinking about something other than what we’re doing. They also found that when people are not thinking about what they’re doing, they’re not as happy as when they’re engaged. In particular, negative mind wandering — thinking negative thoughts, or wishing you were somewhere else — was more likely to lead to unhappiness in their next moments.

Together with Eli Puterman, we studied close to 250 healthy, low-stress women who ranged from 55 to 65 years old and assessed their tendency to mind-wander. We asked them two questions: How often in the past week have you had moments when you felt totally focused or engaged in doing what you were doing at the moment? How often in the past week have you had any moments when you felt you didn’t want to be where you were, or doing what you were doing at the moment? Then we measured the women’s telomeres.

The women with the highest levels of self-reported mind-wandering had telomeres that were shorter by around 200 base pairs. (To put this in context, a typical 35-year-old has roughly 7,500 base pairs of telomeres; a 65-year-old, 4,800 base pairs.) This was regardless of how much stress they had in their lives. Some mind-wandering can be creative, of course. But when you are thinking negative thoughts about the past, you are more likely to be unhappy, and you may possibly even experience higher levels of resting stress hormones.

The negative thought patterns we’ve described are automatic, exaggerated and controlling. They take over your mind; it’s as if they tie a blindfold around your brain so you can’t see what is really going on around you. But when you become more aware of your thoughts, you take off the blindfold. You won’t necessarily stop the thoughts, but you have more clarity. Activities that promote better thought awareness include most types of meditation, along with most forms of mind-body exercises, including long-distance running.

Thought awareness can promote stress resilience. With time, you learn to encounter your own ruminations or problematic thoughts and say, “That’s just a thought. It’ll fade.” That is a secret about the human mind: We don’t need to believe everything our thoughts tell us. Or, as the bumper sticker says, “Don’t believe everything you think.”

Excerpted from the new book The Telomere Effect: A Revolutionary Approach to Living Younger, Healthier, Longer by Elizabeth Blackburn and Elissa Epel. Reprinted with permission from Grand Central Publishing, a division of Hachette Book Group, Inc. © 2017 Elizabeth Blackburn and Elissa Epel.