Recently, Mr. Rafael Santos cited a 2025 study online to try to justify his claim that those who live in the Andes perform worse cognitively. The source does exist; appeared in High Altitude Medicine & Biology, the problem is that the tweet and the article tell quite different stories.
Let’s start with the basics. The message speaks of people who live “more than 2,000 meters,” but the 48 participants in the study resided in Cerro de Pasco, about 4,340 meters away. The difference matters, because the effects of hypoxemia grow with altitude and nothing in the study authorizes extrapolating them downwards. Nor are they about “the Andeans” in general, they are lifelong residents of a single city, recruited with flyers and by word of mouth. The authors themselves describe it as a pilot study.
On the other hand, the study did not put Pasqueños against lower altitude populations. He looked at variation within the same group and found that those who spent more time with low oxygen saturation during sleep, or had a higher hematocrit, responded more slowly on some tests. That’s a difference between individuals, not populations, and it completely changes what can be said.
Where the tweet departs furthest from the paper is in risk-taking. It claims worse performance, but the test used, the BART, involves inflating a virtual balloon; Each pump adds points and each pump increases the probability of bursting. The authors analyzed how much the participants accumulated and found no relationship with nocturnal hypoxemia.
What did lengthen was the reaction time. Taking longer to respond may be clinically relevant, but it is not equivalent to having made worse decisions. In this test, in fact, hypoxemia was not related to the amount of reward obtained.
Furthermore, there remains the question of causality. The design is observational, a photograph at a given moment, and a photograph shows that two things appear together, not that one produces the other.
Nor should these variables be confused with a disease. Nocturnal hypoxemia is a measure of how much oxygen saturation falls during sleep, while hematocrit indicates what proportion of the blood is occupied by red blood cells. In the sample, only a minority met the criteria used for excessive erythrocytosis or chronic mountain syndrome. We are not, therefore, facing a population made up of people with the same medical condition.
The value of the study lies elsewhere. If hypoxemia during sleep is related to slower responses, we are facing a health problem that deserves to be measured and attended to in high altitude areas. What the work proposes is a task for the health system, not a ranking of capabilities.
To be fair, there are laboratory experiments where sea level people, briefly exposed to mild hypoxia, tend to take more risk. But that describes unacclimatized people subjected to acute exposure, which bears little resemblance to those who have lived at altitude for generations. Mixing both scenarios would be making the same mistake in the opposite direction.
Turning a preliminary association into a verdict on millions of Peruvians is using the name of science without having gone beyond the front line.
