The technological revolution that humanity has experienced in recent years has caused great advances in the world of medicine, in the way we communicate, in food cultivation or in the treatment of waste and water. This progress has allowed improving the quality of life of people globally, but has also had consequences that can affect our health and well -being. One of the main consequences has been that most population nuclei have been built around very extensive cities, which has moved us away from nature. In Europe, today more than 70% of people live in urban areas (1) and it is estimated that more than half of the world population lives away from nature (2). In addition, this is intensified with the situation that causes the excessive use of mobile technology in our day to day, which makes us even more difficult to contact nature. Another of the consequences that the technological advance has brought is that the forms of social organization and work have changed in the most developed societies, which has increased the levels of stress, sedentary lifestyle or psychological disorders such as anxiety or depression (3 ).

Given this context, and assuming that the growth of cities and technological progress is unstoppable, society needs to recover part of its essence to be able to build a future in which health is not a toll to pay for progress. In this sense, contact with nature stands as an effective tool to improve people's health. As we saw in a previous article, the so -called "nature pills" can help reduce stress and depression symptoms . For example, in Japan, those known as Shinrin-Yoku or "Basque Baños" are very widespread, where people "submerge" in nature while paying attention to their senses, walk or simply sit down to listen to the sounds of birds, water or trees. Thus, different studies have shown that "forest baths" can help significantly reduce blood pressure (4), anxiety (5) or improve immune function (6). A study showed how 12 men who walked 2 hours in the morning and 2 hours in the afternoon through a tokyo forest a single day increased both the number and activity of the natural cells Killer and reduced their levels of stress markers such as Cortisol and adrenaline. The remarkable thing was that these effects lasted at least 1 week (7).

How long is it necessary to immerse yourself in nature to improve health?

Just as guides-more or less successful-have been developed where optimal doses of physical activity are recommended to improve health (eg 150 minutes of moderate-intense physical activity a week or walk at least 10,000 steps), do Is there an optimal contact with nature? Knowing the potential benefits of exposure to nature, various studies have found doses to improve different aspects of health. For example, it has been proven that a 90-minute walk through nature can help reduce symptoms of depression (8) or that only 20-30 minutes seem to be enough to improve stress (9). In this sense, a recent study published in Scientific Reports that analyzed more than 20,000 people from the United Kingdom saw how those who passed at least 120 minutes in nature a week had a greater probability of reporting good health and well -being (10)  ( Figure 1). Exhibitions above 2 hours did not involve a leap in the reported benefits. That is, the study suggests that spending 2 hours a week in nature could be a goal that, like eating 5 pieces of fruit and vegetables or overcoming the 10,000 daily steps barrier, benefits our health. In addition, a significant fact was that the benefits were very similar in young and old and in people living in poor or rich areas. Another interesting aspect is that it did not matter if exposure to nature was done regularly during the week or in a single day. If time is not available to be in nature every day, the study suggests that for example go 2 hours the weekend reports similar benefits that expose yourself 20 minutes every day.

Although they are promising results, the study does not show a cause-effect relationship. For example, in the improvement of reported health, it could intervene that those who spent more time in nature carried out more physical activity, although there is evidence that indicates that exercising in nature reports greater benefits at the psychological level than to perform it in closed spaces ( 11). These findings must be a starting point to study the causes for which nature improves health, although it is true that, seeing the results shown, increasing contact with nature seems a safe path to recover part of the health lost by the Western lifestyle.

Possible mechanisms by which nature improves health

There are two psychological theories that partly explain the mechanistic basis of the restorative effects of exposure to nature. The theory of restoration of attention focuses on the ability of nature to restore attention through unconscious cognitive processes. In contrast to the constant stimulation that induce urban environments, nature does not require directed attention and, at the same time, causes pleasure and relaxation (12). The stress reduction theory postulates that nature can be perceived as less threatening and, therefore, less exciting, which leads to the recovery of stress levels through an autonomous response of the nervous system to nature ( 13). At the evolutionary level, we perceive nature as a safe environment that allows to increase the activity of the parasympathetic nervous system, whose activity is depressed in people with stress or immune alterations.

In short, recovering contact with nature could help reduce stress levels and improve our physical and mental health. Small pills of nature could mitigate the negative impact of unstoppable growth of cities and their associated consequences: noise, pollution, sedentary or stress. In the words of naturalist David Attenborough: “ In this world a species can only prosper when everything around him prosper too. We need to stop departing from nature to become part of it . ”

References:

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