Depression is already a global health problem. In addition, its approach is very complex, since it has an etiology in which many factors intervene, many of which are difficult to modify. In the first place, it is a disease with a high genetic load, so that those with family history of depression have a greater risk of suffering the disease (1,2). However, there are other environmental elements that are decisive in their appearance. For example, the socioeconomic and educational level, the quality of the diet, the levels of physical activity, exposure to pollution (3), or even having access to green areas or natural places (4). In this way, people with less economic resources living in poor neighborhoods or in contaminated areas, which have precarious jobs, or who in their day to day cannot perform physical activity regularly or eat healthy, have a greater risk of having depression. That is, there are many conditions that we cannot control and that predispose us to suffer a disease that is very disabling. And as we can see, this is especially problematic in the most disadvantaged people.

The pandemic problem

If the current lifestyle adds the uncertainty generated by pandemic or wars, we get a perfect storm. Mental health problems have triggered in recent years. Thus, for example, according to a study published in The Lancet , the Covid pandemic has increased by 27.6% cases of major depression, adding 53.2 million to the cases that had previously already (5). And this has very important consequences for health. Depression is one of the most disabling diseases. A person with depression can barely lead a normal life. To visualize this impact, there is a parameter called AVAD ( years of life adjusted for disability ) that is used to express the years of life lost due to the disease. Thus, for example, following the pandemic, the AVAD for major depression worldwide has reached 49.4 million years (5). This means that almost 50 million years of life worldwide have been lost due to depression.

What factors can we modify?

Although it is very difficult to address in an integral way all the factors that trigger the disease, we can modify some of them. One of the main modifiable risk factors associated with depression is sedentary lifestyle. Increasing physical activity levels helps to prevent depression (6.7). Thus, according to a meta -analysis of prospective studies (8), people with higher levels of physical activity have 17% less risk of depression compared to people who barely move in their day to day. However, although we know that physical activity attenuates the risk of suffering the disease, we do not know with certainty what is the optimal dose-response.

To try to answer this issue, an investigation published in Jama Psychiatry has carried out a meta -analysis of 15 prospective studies in which more than 2 million people included (6). It is the first to date to calculate the dose-response of the association between physical activity and depression.

What were the results?

The researchers found an inverse curvilinear association, so that the greatest benefits were seen when people went from being completely sedentary to move, even if it were just a bit . That is, as can be seen in Figure 1, meet the recommendations of physical activity (do ~ 9 METS/Hour of physical activity a week, or what is the same, do 2 and a half hours of moderate physical activity a week) associated with 25% less risk of depression. But the striking thing is that benefits were found even with half the dose. Compared to not moving, doing physical activity of moderate intensity 1 hour and fourth a week was associated with 18% less risk of depression compared to not moving anything (Figure 1). In summary, according to this data, the difference between moving and not moving involves a very considerable benefit in terms of protection against depression. This shows that for little, the movement offers very important benefits for our mental health.

A very interesting issue that addresses this research is to calculate the number of people who could have avoided the disease if they had been active. The figure reaches 11.5%. That is, if 1 in 10 people with depression had followed the current recommendations of physical activity (2 and a half hours of moderate intensity), the disease could have been avoided.

Possible mechanisms for which the exercise could be an anti-depressive

The truth is that doing a lot of physical activity does not prevent you from suffering from depression, but it seems to be an important factor in having optimal mental health. The health of our nervous system is conditioned by the health of muscle tissue, the largest organ of our body. Although the mechanisms by which exercise protects us from depression are not known exactly The brain Thus, for example, lactate , one of the main metabolites produced when we exercise, especially at high intensity, reduces the risk of depression, and in the event that we suffer it, attenuates the symptoms (in this article we describe the mechanisms described).

On the other hand, exercise could also act on another key route in depression: that of quinurenin . This protein, which is metabolized from tryptophan in the liver, if accumulated in the central nervous system can induce neuronal death and increase neuroinflammation, and therefore depression (9). And this is where the exercise appears. When we exercise, the expression of PGC1α is increased, a factor that, in addition to improving mitochondrial biogenesis, increases the expression of the quinurenin transferase enzyme (Denominadata Kat) (10), which converts neurotoxic quinurenine (Kyn) into quinurnal acidic acid (Knya), which is neuroprotective. In this way, exercise could help reduce this neurotoxic metabolite in the nervous system, improving the symptoms of depression.

Conclusions

Depression is currently a global health problem that has a marked social character, since its prevalence is accelerated by the lifestyle prevailing in the developed world. Therefore, public policies must be aimed at reducing risk factors that increase the risk of suffering from it. Improving access to education, public health, reducing pollution and social inequality indices, or promoting a healthy lifestyle in all areas of society, are measures that could help solve the problem from its root.

Assuming the multifactorial character of the disease, sedentary lifestyle, which is also a growing problem today, is a factor that increases the risk of depression. Therefore, performing physical activity of moderate intensity, even if it is only 1 hour a week, has a protective effect. Preserving muscle activity should be a priority objective to prevent and treat the disease. The muscle acts as an anti-depressive pharmacological bank.

References:

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