Physically active adults are less inclined to be depressed, say Oxford and Yale researchers

But we already knew that, didn't we?

  • American adults that exercise spend an average of 18 fewer days depressed every year.
  • The large-scale study includes data from over 1.2 million Americans over a five-year period.
  • The researchers note that too much exercise negatively impacts mental health.

Weekends in Los Angeles are dominated by physical activity: hiking, surfing, running, cycling, yoga. It's easy to affix stereotypes to this city's denizens, yet year-round sunshine affords residents every opportunity to stay fit. Many take advantage; staying active is part of the culture.

Not that everyone partakes, of course, but lack of opportunity can never be an excuse. Having grown up on the East Coast, I recall when outdoor physical activity was seasonal. You have to work harder during winter months to maintain the same fitness output. Those who endure the ravages of winter to make it to the gym seemed happier for it.

Such speculation was recently put to the test by researchers at Oxford and Yale. In a study of more than 1.2 million Americans, they discovered physical fitness is more important to your mental health than how much money you make. To be exact: exercisers are, on average, depressed 35 days a year; for non-active participants that number is 53 days.

Using data between 2011–2015 provided by the Centers for Disease Control and Prevention Behavioral Risks Surveillance System, researchers found that physically active adults self-report feeling depressed much less than couch potatoes. They point to the fact that exercise is correlated with numerous health benefits, including reduced risk of overall mortality, cardiovascular disease, obesity, stroke, and cancer.

If you feel good, your perspective tends to follow.

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It's not only the diseases you avoid. Exercise is linked with improved musculoskeletal health and stress regulation. Studies centered on mental health have been a bit more ambiguous, though it has long been known that exercise helps curb anxiety and depression. For this study, researchers note that intervention has never been more needed considering that "depression is now the leading cause of global disability burden."

Reducing this burden is the main goal of this research. Thinking outside of the gym, they included 75 types of physical activity in the survey, including golf and gardening. They grouped "mindful exercises," such as yoga and tai chi together—a slightly strange decision, given that even those two disciplines leave distinct imprints on your nervous system. Still, the underlying goal is to better understand the difference between movement versus no movement. The former made a statistically significant impact.

While movement scores above money, the results were actually U-shaped. Three to five weekly sessions of thirty minutes to an hour appears to be the magic zone for achieving optimal mental health. Those working out three or more hours a day did not show better results than those who don't work out at all. There are likely two reasons for this: fatigue, which can drain your emotional output, and obsessive-compulsive disorder, a real problem in gyms. For example, some former addicts devote themselves to the "high" of working out, but really only move their addiction to another focus. Healthier, sure, but incessant anxiety about working out still follows.

Competitors warms up prior to the start of day one of the 2013 Australian National Surf Lifesaving Titles on April 17, 2013 in Gold Coast, Australia. Photo credit: Chris Hyde / Getty Images)

Team sports and cycling proved to be associated with the lowest mental health burden; the "mindful exercises" scored higher on the satisfaction index than walking.

The researchers note that while they believe these results are causal, more research is needed to prove direct links between specific exercises and mental health. Still, they feel comfortable stating the difference between working out and not working out is the same as "between individuals with a difference in household income of more than U.S. $25,000."

Point being: making more money is not necessarily the road to satisfaction. Regular movement is. This makes sense, given that for most of history, survival required physical output more than monetary exchange. There is measurable progress made in building shelter or hunting food; watching a number increase on a screen does not offer the same biological rewards, regardless of how happy we believe money will make us. Another recent study points out that the highest increase in depression and anxiety in recent years has been in the wealthiest demographic.

A rather old lesson, yet one we seem to keep forgetting. The chemistry of satisfaction and self-assurance relies on blood flow, not cash flow. Money is helpful. Movement is necessary.

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  • The finding builds on the hygiene hypothesis, first proposed in 1989.

Are modern societies trying too hard to be clean, at the detriment to public health? Scientists discovered that a microorganism living in dirt can actually be good for us, potentially helping the body to fight off stress. Harnessing its powers can lead to a "stress vaccine".

Researchers at the University of Colorado Boulder found that the fatty 10(Z)-hexadecenoic acid from the soil-residing bacterium Mycobacterium vaccae aids immune cells in blocking pathways that increase inflammation and the ability to combat stress.

The study's senior author and Integrative Physiology Professor Christopher Lowry described this fat as "one of the main ingredients" in the "special sauce" that causes the beneficial effects of the bacterium.

The finding goes hand in hand with the "hygiene hypothesis," initially proposed in 1989 by the British scientist David Strachan. He maintained that our generally sterile modern world prevents children from being exposed to certain microorganisms, resulting in compromised immune systems and greater incidences of asthma and allergies.

Contemporary research fine-tuned the hypothesis, finding that not interacting with so-called "old friends" or helpful microbes in the soil and the environment, rather than the ones that cause illnesses, is what's detrimental. In particular, our mental health could be at stake.

"The idea is that as humans have moved away from farms and an agricultural or hunter-gatherer existence into cities, we have lost contact with organisms that served to regulate our immune system and suppress inappropriate inflammation," explained Lowry. "That has put us at higher risk for inflammatory disease and stress-related psychiatric disorders."

University of Colorado Boulder

Christopher Lowry

This is not the first study on the subject from Lowry, who published previous work showing the connection between being exposed to healthy bacteria and mental health. He found that being raised with animals and dust in a rural environment helps children develop more stress-proof immune systems. Such kids were also likely to be less at risk for mental illnesses than people living in the city without pets.

Lowry's other work also pointed out that the soil-based bacterium Mycobacterium vaccae acts like an antidepressant when injected into rodents. It alters their behavior and has lasting anti-inflammatory effects on the brain, according to the press release from the University of Colorado Boulder. Prolonged inflammation can lead to such stress-related disorders as PTSD.

The new study from Lowry and his team identified why that worked by pinpointing the specific fatty acid responsible. They showed that when the 10(Z)-hexadecenoic acid gets into cells, it works like a lock, attaching itself to the peroxisome proliferator-activated receptor (PPAR). This allows it to block a number of key pathways responsible for inflammation. Pre-treating the cells with the acid (or lipid) made them withstand inflammation better.

Lowry thinks this understanding can lead to creating a "stress vaccine" that can be given to people in high-stress jobs, like first responders or soldiers. The vaccine can prevent the psychological effects of stress.

What's more, this friendly bacterium is not the only potentially helpful organism we can find in soil.

"This is just one strain of one species of one type of bacterium that is found in the soil but there are millions of other strains in soils," said Lowry. "We are just beginning to see the tip of the iceberg in terms of identifying the mechanisms through which they have evolved to keep us healthy. It should inspire awe in all of us."

Check out the study published in the journal Psychopharmacology.