Maybe a sense of calm comes with a walk in the woods surrounded by birdsong or during the quiet of your morning meditation or evening prayer. Maybe the rhythm of knitting or the earthy smell of gardening clears your head.

Science backs up what we know intuitively: Time we spend in nature or on calming practices or hobbies can benefit our mental and physical health. These activities rejuvenate us, right down to our bodys living building blocks: our cells.

A UC San Francisco-based team led byAlexandra Crosswell, PhD, andElissa Epel, PhD, has woven together their own research and studies by others in various fields to connect the experience of, say, painting or practicing yoga to shifts in the nervous system and, subsequently, within our cells. To make this transition, our bodies and minds require certain conditions. But once these are met, the result, they say, isdeep rest.

This truly restorative state one never described before confers benefits unattainable through routine rest and relaxation. In putting forward this concept, the team highlights the regenerative biological processes that protect us as we age.

Deep rest is something our bodies need and deserve, says Epel, a professor of psychiatry and vice chair of psychology. With it, we improve our chances for healthy longevity.

To understand the benefits of deep rest, we must confront its counterpoint: stress. Surveys by the American Psychological Association suggest Americans experience plenty of this stomach-churning state. Almost half of adults who responded to a 2023 survey agreed at least somewhat with the statement My stress makes going to work [or] school increasingly difficult.

Stress, though it can interfere with our ability to function, originated in physiological mechanisms to help us meet challenges whether escaping a pack of wolves or facing fallout from a major work mistake. Just like the fear of being eaten, the threat of losing your colleagues respect can put your body on high alert, triggering a cascade of responses.

Your nervous system hands over control of unconscious processes like breathing and digestion to its in-house crisis response coordinator: the sympathetic nervous system. This shift kicks off a series of energy-demanding changes that prime your body and mind for action. Your heart beats faster. Blood flow increases to your skeletal muscles, which tense up. Your production of hormones, such as cortisol and other energizing chemical messengers, surges. Your alertness intensifies.

Together, these and other shifts help ready you to fight or flee even if youre just anxiously awaiting a reply to your apologetic email while imagining dire scenarios.

A certain degree of stress is inevitable in life, Crosswell points out. After years of studying stress, it became clear to us that we have to stop trying to get rid of it, she says. Stressful events are often outside our control, and our bodies response to them is natural and helpful.

Too much stress, however, can cause harm. She and her colleagues argue that many Americans spend most of their waking hours in a moderately stressed-out state, driven by feelings of uncertainty about the future and lack of control. While no surprise to many of us, the idea the team explores that we experience continual stress represents a new direction in scientific thinking, which has traditionally considered relaxation the default human state.

Ideally, a stress-inducing crisis comes to a quick, clear ending. Maybe your apology at work is accepted, the mistake quickly forgotten. But problems in modern life often dont come to quick, complete conclusions. Your boss may repeatedly deny requests for remote work. You and a loved one may frequently argue. You may struggle financially for years. Under such circumstances, stress can attenuate to a more moderate level, but it doesnt stop.

While less taxing, residual stress still drains you. Maintaining an elevated heart rate or pumping out more cortisol than usual requires extra energy. This energy takes the form of molecules known as ATP, or adenosine triphosphate. Cellular organelles called mitochondria make ATP by using oxygen from the air we breathe to harvest energy from fats, proteins, and glucose derived from food we eat.

Mitochondria are the source of the vital force that brings a cell to life and ultimately gives us our conscious mind, our emotions, saysMartin Picard, PhD, director of the Mitochondrial Psychobiology Group at Columbia University and one of Epel and Crosswells collaborators.

Everything we experience is powered by the energy flow inside our cells, he says, and that flow takes place in mitochondria.

While a single cell can contain hundreds of mitochondria, the organelles can generate only so much ATP for reasons that remain unclear. So when your body goes on alert, a cell diverts its limited ATP supply to carry out the urgent functions the stress response demands, such as contracting the heart or synthesizing hormones. This robs it of energy for more routine but necessary tasks.

Whats more, studies have linked diseases, including diabetes, heart disease, and neurodegenerative disorders, with poor mitochondrial health. Picard suspects psychological stress has a similar effect, with mitochondria sustaining damage and becoming less productive when someone is under chronic strain.

Some prior studies and his own research with mothers caring for children on the autism spectrum, a source of chronic stress, support this idea. In a study led by Epel and described inBiological Psychiatry, Picard and others found that mitochondria in the mothers white blood cells had a reduced ability to transform energy into ATP. Cells face another potential consequence of damaged mitochondria: increased production of a potentially toxic byproduct of making ATP chemicals known as reactive oxygen species (ROS). If not neutralized, ROS can harm our cells.

The effects of chronic stress extend to our genetic material as well. At the tips of chromosomes, repeating segments of DNA form telomeres. With assistance from proteins, telomere caps protect the integrity of these packets of genetic code for as long as they can.

Each time a cell copies its genetic material so it can replicate, its telomeres lose a little DNA and shorten. Research started 20 years ago by Epel, with UCSF colleagues Nobel laureateElizabeth Blackburn, PhD, andJue Lin, PhD, shows that chronic psychological stress further shortens telomeres. This loss is a consequence of exposure to ROS, the release of hormones like cortisol, and inflammation. Molecular studies of cells substantiate this connection: By mimicking long-term exposure to the stress hormone cortisol, Picard has shown that cells respond by revving up their metabolisms, which shortens telomeres and hastens cell death.

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The power of deep rest - University of California