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What part of your body ages most rapidly?

Here’s Why You May Be Aging Faster Than Your Friends

W e all have friends who were born in the same year but look years younger (or older) than we do. Now researchers say that such perceptions aren’t just about outward appearances but about something deeper—the different pace at which each of us ages, and what that means for our health.

In a study published in the Proceedings of the National Academy of Sciences, scientists led by Daniel Belsky, an assistant professor of medicine at the Duke University School of Medicine’s division of geriatrics, describe a panel of 18 measures tested in 20- and 30-year olds that showed how quickly they are aging. The markers proved to be a good indicator of physiological age; they mirrored the biological effects of aging found in older people. But they were also good markers of physical age, meaning that those who aged faster also looked older, according to unbiased assessments by random people looking at their photos.

Most studies on aging, and the factors that affect aging, come from investigations of older populations, says Belsky. And in most cases, the chronic diseases or physiological changes that come with aging are already well established in these groups. But it’s clear that aging doesn’t happen overnight; rather, it occurs gradually over a period of decades, much like water affects the shape of riverbanks or stones over time. It’s not obvious on a day-to-day basis, but can be dramatic if several years have passed.

In the study, 954 people born in 1972 or 1973 in Dunedin, New Zealand, agreed to participate in a study that followed them from age 26 to age 38. Each participant agreed to be tested on a range of 18 different factors that earlier studies have linked to aging, including blood pressure, lung function, cholesterol, body mass index, inflammation and the integrity of their DNA. Based on their scores on these measures, researchers calculated a biological age for each volunteer. They did this again when the people in the study were 32 and 38 years old, and combined them to calculate the pace at which each person was aging.

Some people were biologically older and aging faster than others, despite being the same chronological age. Not only that, but the researchers showed, by giving the 20- and 30-somethings the same tests of balance and thinking skills that gerontologists give for older adults, that these aging changes were the same as those occurring later in life.

Though some people really were biologically older than they are, the good news is that some were younger than their chronological age and aging more slowly than they should be. Comparing the slower and faster aging groups should reveal some hints about how to keep aging in check. And of the factors that influence aging, says Belsky, the vast majority, as much as 80%, aren’t genetic and therefore well within our control. (Even the 20% that’s DNA-based is modifiable to some extent.) “This is just the beginning,” he says. “The next step is to figure out what knowing this information helps us to do. One of the things it can help us do is identify the causes of accelerated aging so that we might slow it down. And the other thing it can help us do is evaluate therapies that slow down aging.”

Having a way to measure, relatively accurately, the pace at which people age provides a good way of tracking whether any anti-aging treatment works or not. Some of those keys to youth likely won’t be surprising; given the 18 factors that the scientists studied, they will probably involve habits like having a healthy diet that’s low in fat and salt, maintaining a healthy weight, reducing stress, having a strong immune system and getting regular exercise. Not smoking, or quitting smoking may also play a role. To find out, Belsky says he will continue to follow the study group and re-evaluate them again when they are 45. The researchers are charting the participants’ diet, exercise and other behaviors. “We can start to evaluate which behaviors are working to slow down aging,” he says, by seeing which changes slow down the pace of aging. “It’s a tremendous opportunity to begin to sort things out.”

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How the Brain Changes With Age

Sand hourglass next to a calendar

Our bodies change in noticeable ways as we age. Our hair grays, our skin wrinkles and loses its elasticity. Less obvious are the changes happening in our brains.

Much like muscles and joints, certain cells in our brains can stiffen up too, as evidenced in a recent study in mice. This is just one of many ways our brains change as we age – from declines in memory and cognitive abilities, all the way down to microscopic changes to brain cells and chemistry.>

Cognitive Changes

The normal aging process brings subtle changes in cognitive abilities. Committing new information to memory and recalling names and numbers can take longer. Autobiographical memory of life events and accumulated knowledge of learned facts and information – both types of declarative memory – decline with age, whereas procedural memories like remembering how to ride a bike or tie a shoe remain largely intact.

Working memory — the ability to hold a piece of information in mind, such as a phone number, password, or the location of a parked — also declines with age. Some studies suggest a slow decline starts as early as age 30. Working memory depends on the rapid processing of new information rather than on stored knowledge. Other aspects of this kind of fluid intelligence, such as processing speed and problem-solving, also decrease with age.

Certain aspects of attention can become more difficult as our brains age. We may have a harder time focusing on what our friends are saying when we’re in a noisy restaurant. Our ability to tune out distractions and focus on a particular stimulus is called selective attention. Splitting our focus between two tasks – like holding a conversation while driving – also becomes more challenging with age. This type of attention is called divided attention.>

But it’s not all downhill after age 30. In fact, certain cognitive abilities improve in middle age: the Seattle Longitudinal Study, which tracked the cognitive abilities of thousands of adults over the past 50 years, showed people actually performed better on tests of verbal abilities, spatial reasoning, math, and abstract reasoning in middle age than they did when they were young adults.

Contrary to the adage that you can’t teach an old dog new tricks, there is growing evidence that we can and do learn throughout our lives. Neuroscientists are learning our brains remain relatively “plastic” as we age, meaning they’re able to reroute neural connections to adapt to new challenges and tasks.

Structural Changes

All of these alterations in cognitive ability reflect changes in the brain’s structure and chemistry. As we enter midlife, our brains change in subtle but measurable ways. The overall volume of the brain begins to shrink when we’re in our 30s or 40s, with the rate of shrinkage increasing around age 60.

But, the volume loss isn’t uniform throughout the brain — some areas shrink more, and faster, than other areas. The prefrontal cortex , cerebellum , and hippocampus show the biggest losses, which worsen in advanced age.

Our cerebral cortex , the wrinkled outer layer of the brain containing neuron cell bodies, also thins as we age. Cortical thinning follows a pattern similar to volume loss and is especially pronounced in the frontal lobes and parts of the temporal lobes .

The areas of the brain that experience the most dramatic changes with age are also among the last to mature in adolescence. This has led scientists to propose a “last in, first out” theory of brain aging – the last parts of the brain to develop are the first to deteriorate. Studies of age-related changes to white matter support this hypothesis. The first of the brain’s long-distance fibers to develop are the projection fibers connecting the cortex to lower parts of the brain and spinal cord. Fibers connecting diffuse areas within a single hemisphere — called association fibers — are the last to reach maturity and show the steepest functional declines with age.

Neuronal Changes

Changes at the level of individual neurons contribute to the shrinkage and cortical thinning of the aging brain. Neurons shrink and retract their dendrites, and the fatty myelin that wraps around axons deteriorates. The number of connections, or synapses, between brain cells also drops, which can affect learning and memory .

Although synaptic changes are selective and subtle, their effect on cognitive decline is believed to be greater than the effects of structural and chemical changes. In the prefrontal cortex and hippocampus, scientists have observed alterations in dendrites, the branched extensions of nerve cells that receive signals from other neurons. With increasing age, dendrites shrink, their branches become less complex, and they lose dendritic spines, the tiny protuberances that receive chemical signals.

In a study of rhesus monkeys, scientists found the aging process targets a certain class of spines called thin spines. These small, slender protuberances are also highly plastic structures, extending and retracting much more rapidly than the larger “mushroom” class of spines. This has led scientists to speculate that thin spines might be involved in working memory, which requires a high degree of synaptic plasticity. The loss of thin dendritic spines could impair neuronal communication and contribute to cognitive decline.

Finally, the formation of new neurons — a process called neurogenesis — also declines with age. Although scientists once thought neurogenesis came to a halt after birth, we now know that two brain regions continue to add new neurons throughout life: the olfactory bulbs and the dentate gyrus of the hippocampus. But the jury is still out on these findings — in a 2018 study , researchers failed to find any evidence of new neurons in adult brains. They suggested neurogenesis is rare in adults or that it happens to such a small degree that it’s undetectable. And, even if new neurons do appear later in life, scientists don’t know if they could integrate into long-established brain networks or affect cognition. Still, studies in mice have found that strategies to boost neurogenesis, such as regular exercise, can improve cognitive function.

Chemical Changes

As we age, our brains may also generate fewer chemical messengers. Several studies have reported that older brains synthesize less dopamine, and there are fewer receptors to bind the neurotransmitter. One study found 60- and 70-year-olds with mild cognitive impairment had less serotonin in their brains, and the researchers wondered whether manipulating serotonin levels might help prevent and treat memory loss.

Our brains undergo myriad changes during the aging process. However, scientists are learning every day how adopting a healthy lifestyle can delay or minimize the negative consequences of these changes.

Why Is Colorectal Cancer Rising Rapidly among Young Adults?

Doug Dallmann was in his early thirties when he first noticed blood in his stool.

“But, since it only happened occasionally and didn’t cause any pain, I didn’t give it much thought and never brought it up with my doctor,” he wrote in a personal account of his experience.

A few years later, when the bleeding became more frequent and intense, he decided to get it checked out. He was told that the cause was tiny rips in his intestines, which can’t really be treated.

“I just figured it was my lot in life to live with blood in my stool, and returned to ignoring it,” he wrote.

But then he started feeling sharp pains in his pelvis and knew something was seriously wrong. At his annual physical, it didn’t take long for his doctor to find the tumor. At just 40 years old, he was diagnosed with stage 3 rectal cancer.

Unfortunately, Dallmann’s experience reflects a growing trend seen across the country. Since the 1990s, the rate of colorectal cancer (which includes cancers of the colon and rectum) has been rising steadily among adults younger than 50. Not only that, but more younger people are dying from the disease.

This rapid increase is especially puzzling because the rate of colorectal cancer has plummeted among older adults—largely due to regular colonoscopies and lower rates of smoking.

“We don’t understand a lot about the causes, the biology, or how to prevent early onset of the disease,” said Phil Daschner, a program director in NCI’s Division of Cancer Biology. “And that’s important to learn more about because it may affect [approaches for] the treatment and survivorship of early-onset colon cancer.”

In September, more than 400 leading scientists from academia, industry, and government, along with patient advocates, gathered online to exchange ideas and information about colorectal cancer in younger adults. The goal of the think tank, organized by NCI and the National Institute of Environmental Health Sciences (NIEHS), was to identify research priorities that address important questions about the disease.

Although the participants discussed several different aspects of early-onset colorectal cancer—including prevention, treatment, and survivorship—identifying risk factors and causes for colorectal cancer in younger adults emerged as the top priority.

Rising Rates around the World

Nearly 18,000 people under the age of 50 will be diagnosed with colorectal cancer this year in the United States, said Rebecca Siegel, M.P.H., of the American Cancer Society. But the disease is still relatively rare, affecting far less than 1% of younger adults.

Some groups have been hit by the rising trend more than others. For instance, although people of all races can develop colorectal cancer at a young age, the spike has mostly been seen among Alaska Native, American Indian, and White people.

However, Black people are still more likely to get colorectal cancer at a young age than White people, even though the gap is shrinking, said Nathan Ellis, Ph.D., of the University of Arizona Cancer Center.

The United States isn’t the only country facing the alarming rise in early-onset colorectal cancer, noted Jeffrey K. Lee, M.D., of Kaiser Permanente Northern California. Similar trends have also been documented in Canada, New Zealand, Australia, and some parts of Europe and Asia. In most of these places, the number of cases in younger adults started trending upward around 1995.

Causes of Colorectal Cancer in Young Adults

Experts don’t know what’s causing the jump in colorectal cancer among young adults. But they do know some factors that raise the risk of colorectal cancer in older adults, including obesity, physical inactivity, and smoking.

“Some of those [risk factors] have become more common over the last 45 years, along with this rise in early-onset cases,” said Daschner, who helped plan the think tank. So, it’s possible that some of the same factors are responsible for the rise of early-onset disease, he noted.

On the other hand, there may be a set of unique risk factors for colorectal cancer in younger adults that researchers haven’t yet identified, he added.

Although certain genetic conditions—like Lynch syndrome and familial adenomatous polyposis—raise the risk of developing colorectal cancer at a young age, only 10% to 20% of early-onset colorectal cancers are caused by inherited factors, explained Kimmie Ng, M.D., of Dana-Farber Cancer Institute.

When the incidence of a disease changes by generation, that suggests the culprit is something in the environment, rather than something biological, Dr. Ng added, with many other meeting participants agreeing.

Diet, Gut Bacteria, and Inflammation

Most of the discussions about the possible causes of early-onset disease converged on three interrelated factors: diet, bacteria in the gut, and inflammation.

There’s mounting evidence linking an unhealthy diet—in particular, one high in processed meat and fat, and low in fruits and vegetables—to early-onset colorectal cancer.

Likewise, several studies have found that being overweight or obese may raise someone’s chance of getting early-onset colorectal cancer. Using data from electronic health records, Nathan Berger, M.D., of Case Comprehensive Cancer Center, found that half of younger adults with colorectal cancer were overweight and 17% were obese.

Unhealthy diets have become more common in past decades, the researchers pointed out. And the number of children and adults who are overweight or obese continues to climb.

In addition, Americans are spending more time sitting and less time being active. Studies have found that more TV time is also linked to a higher risk of early-onset colorectal cancer, said Yin Cao, Sc.D., M.P.H., of Washington University in St. Louis. But it’s not clear if that’s because being less active can lead to being overweight.

Other scientists have turned their focus to bacteria that live in the gut, also called the gut microbiome. Certain types of bacteria have been pegged as accomplices in the growth and spread of colorectal cancer, and some may affect how well certain cancer treatments work.

In lab studies, toxins from several types of bacteria that are normally found in the human gut caused cancer in the intestines of mice, explained Cynthia Sears, M.D., an infectious disease expert from Johns Hopkins University.

An illustration of how the gut microbiome influences health.

Perhaps not surprisingly, gut bacteria are affected by the food and chemicals we eat, drink, and breathe. Studies have shown that diet, obesity, exercise, and some drugs (such as antibiotics) can all change the number and types of bacteria in our guts.

Unhealthy diets and gut bacteria are connected in another way, too. Both can lead to inflammation—the body’s reaction to injury, disease, or irritation. In one study of mice, a high-fat diet triggered gut inflammation and accelerated the growth of tumors in the intestines.

As for gut bacteria, some bacterial toxins intensify inflammation, Dr. Sears noted. Studies have also shown that certain gut bacteria can recruit immune cells that help cancer grow, as well as block immune cells that fight cancer. Inflammation can also generate harmful chemicals that can mutate DNA and promote cancer, explained Dr. Ng.

In addition, certain chronic diseases, including irritable bowel syndrome, Crohn’s disease, and diabetes, can cause inflammation in the gut. Half of younger adults with colorectal cancer also have a chronic condition that can cause inflammation in the gut.

The effects of these factors could start very early in life—in childhood, infancy, or even in the womb—noted Caitlin Murphy, Ph.D., M.P.H., of the University of Texas Southwestern Medical Center.

Chemicals in the Environment

Scientists are also examining factors in the environment as potential causes of early-onset colorectal cancer. Such factors include things like air and water pollution, chemicals in soil and food, and pesticide use.

The National Toxicology Program, led by NIEHS, has identified 18 chemicals that cause cancer in the intestines of mice or rats, said NIEHS Director Rick Woychik, Ph.D., who also heads the National Toxicology Program. Some of these chemicals might damage DNA, potentially leading to harmful mutations in cells of the colon and rectum.

Other chemicals may have more indirect effects, pointed out Barbara Cohn, Ph.D., M.P.H. of the Public Health Institute. For example, mixtures of certain environmental chemicals (sometimes called endocrine disrupters and obesogens) can disrupt the body’s metabolism, leading to obesity, she said. Even though some of those chemicals are now banned, their use in earlier decades could have effects later in life for people who were born back then, Dr. Cohn explained.

In addition, some environmental chemicals may have harmful effects on the complex assortment of bacteria in the gut, Dr. Woychik noted.

People are exposed to many chemicals at the same time, some of which may interact in different ways, he added. So, it’s important to consider all of an individual’s environmental exposures over the course of their life, including exposures in the womb, said Dr. Woychik. How those chemicals interact with a person’s genetic and epigenetic characteristics is also important, he added.

Informing Approaches for Prevention and Treatment

Defining the causes and risk factors for early-onset colorectal cancer will likely help inform approaches for prevention, screening, and treatment, Daschner said.

For instance, health care professionals could recommend lifestyle changes or more frequent screening tests to people who, because of their exposures, are at higher risk of developing colorectal cancer at a young age.

A few medical organizations have lowered the recommended age to start colorectal cancer screening from 50 to 45. For those younger than 45, tailoring colorectal cancer screening approaches to each person based on their risk factors (called precision screening) may improve the efficiency and cost-effectiveness of screening, said Dr. Lee.

Homing in on the causes and risk factors will also help scientists uncover the underlying biology of early-onset colorectal cancer. More specifically, it can help scientists pinpoint specific molecules that drive the growth of colorectal cancer in young people. Which, in turn, could hatch new ideas for colorectal cancer screening and treatment.

For example, some screening tests check for specific molecules made by colorectal cancer or polyps (growths that could turn into cancer). Knowing which molecules are key to the growth of early-onset tumors could help researchers design screening or diagnostic tests that are tailored for younger adults. It could also help them develop treatments that target those key molecules (an approach known as targeted therapy).

First, More Awareness

Although the coronavirus pandemic forced this long-planned think tank to be held online, it still brought together people with expertise in many different areas, Daschner said.

“We hope the meeting will spur research collaborations across these different areas” to make more progress, he added. To continue to promote research in this area, NCI has issued a funding opportunity for research on the causes of early-onset cancers.

But for now, many at the meeting agreed that there’s an even more pressing step: spreading awareness of the early warning signs of colon cancer in younger adults.

Both young people and doctors need to shed the notion that colorectal cancer is an “old person’s disease,” several meeting participants stressed. People should get used to looking at their stool and noticing changes, they noted.

“In retrospect, I wish I had paid more attention to the symptoms,” noted Dallmann, the young man who initially ignored his symptoms and was misdiagnosed for years. That’s why he continues to share his story. It’s inspired several family members and friends to get screened, he said, and a few were found to have polyps.

“It feels like a small repayment for the amazing outpouring of support I received from my friends, co-workers, families, my cancer support group, and those in the online cancer community who I’ll likely never meet,» he said. «I hope that I can continue to pay it forward.”

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