The Happiness Theory

With this review I will try to convince you that there is no better place to live other than a Tropical country. Three scientific-based arguments are enough to explain why some surveys consider developing countries as the ones with the highest levels of happiness [1] such as Nigeria, Mexico, Venezuela and El Salvador.

My first argument is the easiest to explain and by the moment is based only in one paper published on October, 2010 in the Journal of Psychopharmacology by Dr. Christopher Lowry, an expert in the area of behavior-associated molecular biology. In his article [2] he found a subpopulation of serotonergic neurons that are thermosensitive and form part of a pathway regulating behaviour. He proposed that the dysregulation of these neurons plays a role in stress-related neuropsychiatric disorders, including anxiety and affective disorders. That would be, actually, the explanation why a hot bath in the evening, a sauna, a common sunny day or a sweater at the right moment and other sensations of warmth may alter neural circuits controlling mood and even serotonergic circuits.

The second observation is the well known "Hygiene hypothesis", which says that the increasing prevalence in several chronic inflammatory disorders in developed countries are a consequence of the new life-style people have. Living far away of harmless organisms associated with soil, untreated water and fermenting vegetable matter, the immune system generates an aggressive immune response when people are exposed to those organisms once they are adults [3]. Looking to the evolution, these non-pathogenic organisms need to be tolerated because they are harmless and were present in food and water throughout human evolution.

Other observation we have to take into account is the widespread presence of helminths in developing countries but almost absent from developed countries [4]. The helminth parasites need to be tolerated because, although not always harmless, once they are established in the host any effort by the immune system to eliminate them is likely to cause tissue damage.

With these ideas in mind it is time to remember that some stress-related psychiatric disorders,

particularly depression and anxiety, are associated with markers of ongoing inflammation. Moreover, proinflammatory cytokines can induce depression. Therefore, some psychiatric disorders in developed countries might be attributable to failure of immunoregulatory circuits to terminate ongoing inflammatory responses. That correlates perfectly with data from the WHO where most of the cases were reported from Europeans and north-Asian countries and no Tropical countries [5].

My last argument is harder to follow but I will try to do my best. A very recent article published in PNAS last February explains that mice with no contact with any kind of bacteria during their whole life showed different behaviors compared to controls (mice with a standardized microbiota) [6] they showed, indirectly, that the contact with bacteria not only contributes with the correct development of intestinal cells (as it was already known) but also has implications in the host psychology and promotes drastic changes in expression levels of many genes in specific brain regions.

Now, it is time to think how different could be the environmental bacteria we around us in our first week of life. Only in developing countries like Mexico we have to deal with all sort of solid residues in the streets (here is a photo) and the 'fecalismo'. But apart from the harming microorganisms other kind of bacteria enter very often into our body and could help us to learn better and to make us happier: Mycobacterium vaccae.

The same man, C. Lowry, found 4 years ago that M. vaccae stimulated growth of some neurons that resulted in elevated levels of serotonin when injected to mice. Last year, in the 110th Annual Meeting of the American for Microbiology, Dorothy Matthews showed that M. vaccae ingested improved learning in mice [7]. The question is, where does M. vaccae is naturally present? In the soil. And where do people live close to soil instead of roadways or concrete? In Tropical Countries!

To sum up, Tropical countries have the perfect weather to activate thermosensitive neurons serotonin-producers (and the optimal temperature to growth M. vaccae, 21-26°C), it is less frequent to get inflammatory disorders like allergies, autoimmunity or inflammatory bowel disease and it is frequent to get in contact with certain soil-associated bacteria/fungi with learning-improvement capabilities.

This is a writing with NO academic purposes.

1. Asking 'how happy they are' or 'how satisfied they are' here.

2. That warm fuzzy feeling: brain serotonergic neurons and the regulation of emotion, here.

3. The hygiene hypothesis and psychiatric disorders, here.

4. How to Cure 1 Billion People? -- Defeat Neglected Tropical Diseases, here.

5. From Wikipedia with collected information from the WHO, here.

6. Normal gut microbiota modulates brain development and behavior, here.

7. The video, here.