Exercise is good for health. Many studies show that people who exercise are less likely to develop metabolic disorders, such as obesity, diabetes, and cardiovascular disease. This is one reason that exercise is so strongly recommended.
The same is true in relation to mental health. A study of 1.2 million Americans found that those who exercised had 43 percent fewer days of poor mental health, even after controlling for physical and sociodemographic characteristics.1 This study found that any type of exercise was better than no exercise, but that the largest benefits were seen for team sports, cycling, and aerobic and gym activities. The optimal “dose” was forty-five minutes, three to five times per week.
Most people stop there. That’s enough information to make a recommendation. If someone exercises for forty-five minutes, three to five times per week, that should solve the problem.
I truly wish it was that simple, but it’s not. I’ve seen many patients who exercise regularly and still have crippling schizophrenia or depression. I want to explore the nuances of being active. Giving simple explanations with simple answers isn’t going to address our mental health problems. If people follow the “forty-five minutes three to five times a week” advice and don’t see results, they give up in frustration and disappointment. Don’t worry if you’re an exercise advocate—I’m still going to recommend exercise in the end.
The first thing to highlight was that the study with 1.2 million people was a correlational study. As you know by now, correlation doesn’t equal causation. It’s possible that people who exercise already have good mental and metabolic health, and that allows them to exercise. This would be reverse causation.
To illustrate how complicated this can all be, I’ll tell you about another study. This one followed 1,700 women at midlife for twenty years to see if exercise prevents cognitive decline.2 Most people would assume it does. However, after controlling for socioeconomic characteristics, menopause symptoms, hormone therapy use, and presence of diabetes and hypertension, they found that exercise didn’t make any difference in cognitive symptoms. They concluded that “physical activity observed in later life may be an artifact of reverse causation.” So, the news headline for this study is that exercise doesn’t prevent cognitive decline. But this isn’t so clear-cut. They “controlled” for diabetes and hypertension, as though exercise is independent of these variables. We know that it’s not! Exercise decreases the likelihood of both, and may thereby decrease the risk of cognitive decline, too. We know they are all interrelated. And yet, some researchers and academic journals assume they aren’t.
Exercise has been studied as a treatment for mental disorders, with depression being the most studied illness. The results are mixed, with some studies showing benefits and others not. A 2017 meta-analysis looking at exercise as a treatment for major depression included thirty-five studies with almost 2,500 participants.3 Their conclusion: “Trials with less risk of bias suggested no antidepressant effects of exercise and there were no significant effects of exercise on quality of life, depression severity or lack of remission during follow-up.” That’s disappointing!
And yet the World Health Organization begs to differ. They issued a report in 2019 entitled Motion for Your Mind. They summarized their findings as follows: “A review of the evidence for the benefits of physical activity for people with depression, schizophrenia and dementia indicated improved mood, slowed cognitive decline, and delayed disease onset . . . ”4
So, what are we supposed to believe? Does exercise help or not? It’s tempting to err on the “safe” side and tell everyone to exercise, but if it doesn’t actually work, that just sets people up for failure and makes the person recommending it seem less credible.
In otherwise healthy people, it’s known that exercise can improve metabolic health. It’s known to induce both mitochondrial biogenesis and mitophagy—the two things we are looking to do. This occurs not only in muscle cells but also in brain cells. Increasing mitochondria in brain cells should be helpful. So why don’t treatment studies consistently show a benefit?
One reason may be insulin resistance. A study published in Cell found that it may block the benefits of exercise. Researchers had thirty-six people with varying levels of insulin resistance exercise and measured a plethora of biological measures before and after. They found that there were significant differences in energy metabolism, oxidative stress, inflammation, tissue repair, and growth factor responses, with most of these beneficial processes being dampened or even reversed in those with insulin resistance.5 As I’ve already discussed, many people with chronic mental disorders have insulin resistance, so this may explain at the cellular level why exercise might be harder for them and why it might not work.
I suspect that the more important issue is that many people are taking substances and/or have lifestyle factors that impair mitochondrial function, and these are interfering with the beneficial effects of exercise.
Athletes, trainers, and coaches have long known that it takes more than just exercise itself to improve performance. All the factors that I discuss in this book play a role. If someone wants to improve their physical performance through exercise, they also need to pay attention to eating a proper diet, getting good sleep, and refraining from alcohol and drug use, among other things. For example, as I already discussed, alcohol can damage mitochondria and prevent mitochondrial biogenesis and mitophagy. This is why we’ve all heard the advice that if you’re training for an important athletic event, or even if you just want to lose weight, you need to stop drinking. Improving metabolism involves many lifestyle factors in combination, not just one.
Medications can also play an adverse role. In theory, any medication that impairs mitochondrial function might prevent exercise from working. One study looked directly at this issue for the commonly prescribed diabetes medication metformin. Researchers had fifty-three older adults participate in twelve weeks of aerobic training and assigned half of them to take metformin and the other half a placebo. Both groups experienced some benefits from the exercise, such as a reduction in fat mass, glucose, and insulin levels. However, improvements in muscle mitochondrial function were abrogated in the people taking metformin. The metformin group had no overall change in whole-body insulin sensitivity, even though the placebo group experienced improvement. These researchers summarized their findings in the title of their study: “Metformin Inhibits Mitochondrial Adaptations to Aerobic Exercise Training in Older Adults.”6 So, in all the studies looking at the effects of exercise for weight loss, diabetes, or mental disorders, we would need to know if any of those participants were taking metformin. If they were, they were likely being set up for failure to improve their mitochondrial function, and this might be the reason some of the studies showed no benefit.
Metformin is one of the “mildest” diabetes medications with the fewest side effects. Many other diabetes medications, including insulin itself, cause weight gain and even more insulin resistance over time. But it’s not limited to diabetes medications. As you now know, some psychiatric medications, especially the antipsychotic medications, are known to cause serious metabolic disturbances and mitochondrial dysfunction. People taking any of these medications will likely fail to get the full benefits of exercise. The research on exercise for mental illness didn’t factor any of this into their studies.
Mitochondria play a direct role in translating exercise into beneficial effects in the brain. When people exercise, one of the benefits is that they usually develop new neurons in the hippocampus from stem cells. This process has been found to be directly related to both mood and cognitive disorders. The growth of these stem cells into new neurons depends upon mitochondria. When researchers genetically manipulated mitochondria to inhibit or enhance their function, the development of these new neurons was inhibited or enhanced, respectively.7 Based on this research, it appears likely that if someone has poor mitochondrial function in this brain region, they may not get the same benefits from exercise that other people get. However, if we can restore their mitochondrial health, it’s possible that we can change this.
As a rule of thumb, exercise can do one of two things: It can help people maintain their current abilities, or it can improve their abilities. This translates into maintaining your current metabolic status or improving it.
Taking a leisurely walk around the block helps people maintain their current metabolic status. This is useful. It’s certainly better than losing strength or ability. However, to improve metabolic capacity, people need to push themselves. They must work toward getting faster, stronger, more flexible, doing more reps, or achieving some other metric of increased capacity. We know that when this happens, the number of mitochondria in their muscle and brain cells increase, and the health of those mitochondria improve as well.
One of the challenges with exercise is that asking people who are metabolically compromised to push themselves involves risk. There are risks of injury and even heart attacks. Therefore, exercise needs to be managed in a safe way. Physical therapists, personal trainers, and others will play an essential role for some people.
The bigger challenge is getting people who are metabolically compromised to follow through with an exercise routine. They lack energy and motivation. Their metabolism is doing this to them. It’s not their fault. Overcoming this inertia can be difficult. Nonetheless, it can be done with support, encouragement, and education.
Exercise as a Treatment
Should everyone exercise? I would say yes. But it’s important to keep in mind that it will be much harder for people with chronic mental disorders, and they may not notice benefits right away. It’s also important to take an inventory of all the factors that might be impairing your mitochondria and metabolism; reducing or eliminating these will allow exercise to work.
Nonetheless, exercise won’t be the answer for everyone. As I’ve been discussing, there are many factors that play a role in metabolic and mental health. Exercise is only one of them. For people with vitamin or hormone deficiencies, for example, exercise isn’t going to solve the problem, but it certainly won’t hurt.
Summing Up
•Exercise can play a role in preventing mental and metabolic disorders.
•Exercise may be more difficult if you have insulin resistance or any condition associated with mitochondrial dysfunction. It may take longer to show benefits. This doesn’t mean it won’t work; it just means that you should try to be patient and not expect immediate results.
•Identifying, removing, and/or reducing substances and lifestyle factors that impair mitochondrial function will be required to realize the full benefits of exercise. These can sometimes negate the benefits of exercise.
•Exercise can be an effective treatment for some people with mental disorders, but for others, it may not be the solution.
•People with injuries or physical limitations should work with their healthcare provider to implement an exercise program safely. This may include working with a physical therapist.
•Even if exercise doesn’t improve your mental symptoms, you should still exercise, as it offers numerous other health benefits. Humans are meant to move.