Moving to high altitude requires a bit of an adjustment. One of the ways our bodies adjust to the low levels of oxygen is by making more red blood cells, which are responsible for transporting oxygen in the body. More red blood cells means that our blood can pick up more oxygen. If this process continues unchecked, however, it can lead to chronic mountain sickness, also known as Monge’s Disease.
Chronic mountain sickness happens when too many red blood cells are produced. As you may imagine, an excess of red blood cells causes the blood to become thicker and increases the risk of strokes, heart attacks, and high blood pressure.
But how have populations who’ve lived for generations at high altitude adapted? A recent review published in Physiology examined this question by comparing how Tibetan and Andean populations have adapted to mountain living. They found that Tibetans do not experience chronic mountain sickness as often as Andeans and they have a lower concentration of hemoglobin, the module within red blood cells that carry oxygen. This also means that they have less oxygen in their blood. Because they have a lower ability to carry oxygen, they simply breath more deeply to bring more oxygen into the lungs. They also have more blood vessels in their muscles, which gives the muscles more opportunities to extract oxygen from the blood. Having lower concentrations of hemoglobin may also protect Tibetans from chronic mountain sickness and reduce their risk of blood clots or heart attacks.
In contrast, about a third of Andeans over the age of 50 produce too many red blood cells, which increases their risk of developing chronic mountain sickness. Premenopausal women appear to be at least somewhat protected from chronic mountain sickness as female hormones inhibit the formation of red blood cells and increase breathing. Menstruation also helps to lower red blood cell numbers as compared to men.
Researchers are working towards identifying genetic variations that help regulate the production of red blood cells in an effort to prevent or treat chronic mountain sickness and other diseases associated with overproduction of red blood cells.
Humans are not the only species that adjust to high altitude by increasing red blood cell numbers. A study of Citril finches (photo above) found that the birds increased their red blood cells by 6% when migrating at high altitude (Borras et al., 2010). This increase in red blood cell production is similar to humans traveling to high altitude from lower elevations.
Researchers were curious whether chickens living in Tibet were also adapted to the high-altitude environment. So, they gathered eggs from Tibetan chickens and reared them either at low altitude (100 m above sea level) or high altitude (2,900 m above sea level). Similar to the finches, the high-altitude chickens had more red blood cells and lower circulating oxygen concentrations. Like humans, chickens that were not native to Tibet produced even more red blood cells at high altitude than the Tibetan-adapted chickens.
FC Villafuerte, TA Simonson, D Bermudez. High-Altitude Erythrocytosis: Mechanisms of Adaptive and Maladaptive Responses. Physiology. 37(4): 175-186, 2022.
A Borras, J Cabrera, JC Senar. Hematocrit variation in response to altitude changes in wild birds: A repeated-measures design. The Condor. 112(3): 622-626, 2010.
H Zhang, CX Wu, Y Chamba, Y Ling. Blood characteristics for high altitude adaptation in Tibetan chickens. Poultry Science. 86(7): 1384-1389, 2007.