Aesop's fable about the dangers of urban life goes something like this: A City Mouse visits his cousin in the country and is shocked at the humble meal they eat. The City Mouse invites the Country Mouse to his home in town, where he promises to serve a delicious feast. But when the Country Mouse comes calling, dangerous and stressful interruptions from dogs and cats prevent them from digging into their meal in peace. Returning to his simple home, the Country Mouse thinks, “Better beans and bacon in peace than cakes and ale in fear.”
The results of new study published in The Journal of Clinical Endocrinology & Metabolism echo Aesop's ancient truth. Researchers from Philipp's University in Marburg, Germany and the University of Namibia demonstrate that the stress of moving from a rural setting to an urban one makes newly urban transplants more vulnerable to diabetes and other metabolic disorders -- at least in the developing world.
"Our findings indicate that people who leave a rural lifestyle for an urban environment are exposed to high levels of stress and tend to have higher levels of the hormone cortisol," said study co-author Dr. Peter Herbert Kann, M.D. Ph.D. in a press release. "This stress is likely contributing to the rising rates of diabetes we see in developing nations.”
Currently, the rates of diabetes in the developing world are increasing; 347 million people around the globe have diabetes, and more than 80 percent of diabetes-related deaths occur in low- and middle-income countries, according to the World Health Organization. WHO also predicts that the condition will become the seventh leading cause of death worldwide by 2030.
Fifty-four percent of the world's population lives in an urban setting, and the numbers are only going to increase, according to the United Nations. By 2050, the UN predicts that 66 percent of all humans will live in a city, with almost all of the rate growth concentrated in Asian and African countries.
Stress isn’t just an emotional state. Prolonged stress and associated feelings of anxiety, fatigue, anger, fear or sadness can have a physical impact on the body. For instance, stress causes the body to release cortisol, a hormone that the Mayo Clinic calls the body’s “natural alarm system." During a stressful situation, your glands will release cortisol to increase blood sugar, which is meant to give more fuel to the brain and help your body repair tissues more easily. It also suppresses different bodily functions like growth, or processes in the reproductive system and the digestive system.
Kann and his collaborators at the University of Namibia examined members of the Ovahimba people, an ethnic group in Namibia that traditionally lived a semi-nomadic lifestyle and raised livestock. They were isolated from the rest of the country for military reasons during South African apartheid, note the researchers, but have recently begun moving into cities.
The researchers measured the cortisol, blood sugar and cholesterol levels of 60 Ovahimba living in Opuwo, a regional capital. They then compared the results to the same measurements of 63 Ovahimba who lived at least 31 miles (50 kilometers) from the nearest town or village.
They found that 28 percent of urban-dwelling Ovahimba had diabetes or another glucose metabolism disorder, while only 13 percent of rural Ovahimbans had the same conditions. The city slickers also had, on average, more than twice the amount of cortisol than the country residents as measured in the morning and at night, as well as worse measures for biomarkers like body mass index, or blood pressure and heart rate before and after physical exertion.
Researchers also noted that rural residents engaged in more intense physical activity than urbanites, while the urbanites reported eating more fast food and dessert than the rural residents. But the researchers argued that the difference in cortisol levels between urban and rural study participants suggest that lifestyle factors like diet and exercise aren’t the only reason for higher diabetes rates in city dwellers.
Now, it's important to note that rural life in Namibia is vastly different compared to rural life in, say, the U.S. or another developed country. Kann notes that the rural Ovahimba people he studied still lived a traditional semi-nomadic lifestyle and ate food that they had either gathered, grown or hunted. He specifically named milk products and maize as staples in their diet. He also describe Ovahimba rural life as "little villages of extended families without shops."
Contrast that with the average American rural resident. While rural residents in the U.S. fall behind their urban counterparts economically and in terms of educational attainment, they nevertheless still live in a developed country; the median annual income for rural Americans is $40,615. Also, while rural America leads a vastly different lifestyle than urban America, the difference is even greater in developing nations, where things like fast food and office jobs are unique to city life.
"We interpret this as a response to psychosocial stress caused by urbanization, modernization, and modification of the social environment (loss of social support and cultural stability, replacement of collectivism with individualism, racism),” wrote the researchers in their study. Their findings support past research that show "low socioeconomic status and unemployment are widespread in developing countries, resulting in high levels of anxiety and chronic stress and 'a state of functional hypercortisolism,'" they concluded.
The study was supported by an unrestricted grant from the diabetes pharmaceutical company Novo Nordisk Pharma GmbH Germany.