12 September 2011

Type 2 diabetes in Mexico's Tarahumara - a people in transition

By Dirk Lund Christensen

Within the last 10 to 15 years diabetes, and in particular type 2 diabetes, has become a serious threat to the health of all societies and populations. People from low- and middle-income societies have the highest incidence of diabetes worldwide and within these societies indigenous people are the most vulnerable. By studying the lifestyle of the Tarahumara in Mexico, researchers hope to learn more about type 2 diabetes and break the health pattern of indigenous populations in transition between traditional and modern lifestyle.

IN THE SIERRA MADRE OCCIDENTAL mountains of Chihuahua, Mexico, reside a people called Tarahumara. This group numbers around 85,000 and is regarded as the most traditional indigenous population in North America living north of Mexico City. A special trait of the Tarahumara is their love of running, and they are often regarded as the best ultra distance runners in the world.

A large segment of the Tarahumara population still follows a seasonal variation of physical activity and diet, but the Tarahumara have also been affected by a lifestyle transition. Physical inactivity, changes in diet towards more fat and simple carbohydrates have resulted in more people becoming obese. The combination of traditional and urbanised lifestyle as well as their large number makes the Tarahumara a good population to learn from.

"The study is a so-called natural experiment, where we influence as little as possible. The population is in its own surroundings and the control groups are chosen on the basis of their existing living conditions," says Dirk Lund Christensen, an associate professor and human physiologist who is leading the team of researchers from Copenhagen. He further explains that the team will be working with two groups of adult Tarahumara - one normal weight and one overweight - over three to five distinct seasons of a calendar year. Within these groups, one half lives completely traditionally and is isolated from city life, while the other half uses nearby towns but has yet to become fully urbanised. The main outcome will be to determine whether or not the risk of developing diabetes is affected by seasons of high levels of physical activity followed by seasons of low levels of physical activity. If a changing activity level can prevent a person from developing metabolic diseases, it would change our understanding of how such conditions develop. "We hope to get to know how the Tarahumara can have a healthy lifestyle that allows them to continue their traditions yet also be a part of modern life, get an education and improve their quality of life. At the same time we hope to use this knowledge in our diabetes research elsewhere. Today we are told to exercise every day, all year round. Perhaps this message could be less black and white," says Lund Christensen.

Pilot study completed

In September and October 2010 a pilot study involving 65 Tarahumara men and women was carried out. Despite the small number of participants the results indicated a moderate prevalence of diabetes and a high prevalence of hypertension - another chronic disease associated with Western lifestyle. The pilot study showed that it is possible to carry out the study and that there is a high level of local interest. The Tarahumara population is pleased about the interest in their health, and the local authorities are looking forward to further collaboration. According to the plan, the results will be handed over to the local health organisations in a layman's version, so that they can share the knowledge with the Tarahumaras and incorporate the findings in their local health programmes.

Facts: Diabetes type 1 and 2

There are two main forms of diabetes, type 1 and type 2. Type 1 mainly occurs in children and adults under the age of 30, and is rare in North American indigenous populations. Type 2 diabetes mainly occurs in adults over the age of 40, but is increasingly common in younger adults worldwide. Type 2 diabetes is highly prevalent in most North American indigenous populations. Both types of diabetes have a genetic and an environmental component.

Project collaborators

The study is a collaboration between the University of Copenhagen (Denmark), Universidad Autónoma de Chihuahua (Mexico), and the MRC-Epidemiological Unit, Cambridge (United Kingdom).

This article is also published in the Profile / GLOBAL HEALTH # 2 magazine.
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