Future Present

Mexico, like scores of countries around the globe, is in the midst of a transition that some believe is the greatest public health challenge facing the world today.

Future Present

About an hour north of Mexico City by car, on a windswept plain near the town of Tula, a quartet of giant stone figures presides over an ancient pyramid. These monumental sculptures—known locally as gigantes—speak of a charged world where gods and goddesses  had the power to bring on rains or ward off disease or generate life itself.

More than 2,000 years after their construction, these weathered beings remind us of the ways human existence has and has not changed. We, too, confront challenges like drought and disease. But we have new threats as well, and in places like Mexico, many of them are a result of what scientists call the “epidemiologic transition”—a theory developed in the 1970s to explain the dramatic health changes experienced by countries as they modernize. Chief among those are a plunge in infectious-disease rates and a coincident surge in chronic diseases.

Mexico could be a poster child. Chronic diseases—many linked to dietary patterns—account for more than two-thirds of the country’s global disease burden. Obesity and diabetes have reached such epidemic levels that by 2050 it’s estimated as much as 20 percent of Mexico’s population could have type 2 diabetes. Chronic respiratory diseases like asthma are on the rise. Cancer rates have spiked. Environmental toxicants threaten both maternal and child health. Access to high-quality health care is uneven. And infectious diseases persist. Not far from the Tula gigantes, cholera broke out three years ago.

To confront these realities, Mexicans need not stone gods but human ingenuity, technological innovation, and “structural interventions,” says Tonatiuh Barrientos-Gutiérrez of the National Institute of Public Health of Mexico, and a former U-M SPH postdoctoral fellow. “We have to rethink the provision of health services.”

Following is a look at some of the top public health issues facing a nation in the midst of an unprecedented transition—one that’s happening not just in Mexico, but around the world.

Urbanization

As the jet from Detroit swoops in over Mexico City, traversing a virtual  jigsaw puzzle of streets and neighborhoods, the enormity of the place overwhelms. At a population of over 22 million, this is the largest metropolitan area in the Western Hemisphere—one of the world’s 35 “megacities,” which collectively occupy just four percent of the earth’s surface.

By 2017, more than half the world’s population is expected to live in vast urban settings like this.

The challenges these places can pose are as gargantuan as the cities themselves: traffic miasmas, unclean air and water, inadequate infrastructure, environmental degradation, and the health burdens that come from millions of people living closely together. Even in pre-Hispanic times, the megalopolis we now call Mexico City was a financial, industrial, and commercial center. Two millennia later, wealth, power, and services remain concentrated here, and the city draws more than 1,000 new residents every day. 

The presence of so many people means Mexico City’s groundwater is increasingly depleted, its air polluted, and water contaminated. “It was really a beautiful place,” remembers Marisa Mazari, coordinator of the graduate program in sustainability sciences at the Universidad Nacional Autónoma de México, who has lived in the city most of her life. “It was surrounded by forests. It was fresh, we could breathe clean air, you could feel free with all the mountains. Now the air is bad, you’re not sure what kind of water you receive, and traffic is terrible.”

The average daily commute in Mexico City is four hours, round-trip. Residents of some neighborhoods spend as many as six hours a day in traffic.

That’s time that could be spent taking walks, exercising, or cooking healthy foods, suggests Tonatiuh Barrientos-Gutiérrez of Mexico’s National Institute of Public Health. Traffic—and the pollution it generates—worsens conditions like asthma and cardiovascular disease and may be linked to both diabetes and miscarriage.

In a city with few green spaces, fresh fruits and vegetables can be costly. Water is another “huge issue,” adds Barrientos-Gutiérrez. “I don’t think I know anyone who feels OK drinking the water from the tap.” Essentially forced to buy bottled water, many Mexicans opt for sugary sodas instead.

“We used to be self-sustaining,” Mazari says, shaking her head. “Now it’s like we’re bringing in everything. We’re bringing in energy, we’re bringing in water. We’re bringing in food.”

Twenty years ago, Mazari coauthored a study of the environmental sustainability of Mexico’s capital and its surrounding basin. “The urban ills that plague Mexico City may be so far advanced as to preclude any viable rescue attempts,” the authors wrote. “[It’s] an ominous prospect for a megalopolis that is paradigmatic of megacities throughout the developing world.”

Obesity

Fast, cheap food abounds in Mexico—especially since the implementation of the North American Free Trade Agreement in the mid-1990s. Like people in other middle-to-high income countries around the world, Mexicans now spend more time in front of their TVs or computers and less time moving, and they consume more soda. Mexico is the world’s leading per capita consumer of sugary beverages today.

The country has one of the highest obesity rates in the western hemisphere. Ten million Mexicans—ten percent of the population—have type 2 diabetes. Rafael Meza, a Mexico City native and assistant professor of epidemiology at U-M SPH who specializes in mathematical modeling, estimates that between 30 and 50 percent of infants born today in Mexico will be diagnosed with diabetes in their lifetimes.

Statistics like these are typical of the epidemiologic transition, which some scientists refer to as the “nutrition transition.” Mara Téllez-Rojo of the National Institute of Public Health of Mexico speaks of the “double burden of nutrition” in Mexico. In parts of the country, there’s undernutrition. At the same time—and often in the same family—there’s obesity.

Téllez-Rojo, together with SPH Professor Karen Peterson and others, directs a longitudinal study, ELEMENT, aimed at clarifying the role of environmental exposures—including nutrition—in fetal and child development. Researchers in the study—a collaboration among U-M SPH, Mexico’s ABC Hospital, and both the National Institute of Public Health and National Institute of Perinatology of Mexico—are especially interested in the dietary patterns of pregnant women.

Peterson, who chairs the SPH Department of Nutritional Sciences, says a key goal of the study is to expedite the diagnosis of diabetes. If the disease can be diagnosed ten years earlier than it is now, she notes, costs could drop and health outcomes improve.

Recently, Mexican legislators imposed both a ten percent tax on sugary beverages and an eight percent tax on hypercaloric “junk” food. Michigan’s Rafael Meza conducted mathematical modeling studies to gauge the probable health impact of the soda tax. He concluded that by 2050, the tax could help prevent between one and 1.5 million cases of diabetes nationwide. His projections helped persuade legislators to pass the tax, which went into effect in 2014. Initial data show the tax has helped lower sugary beverage consumption by six percent. Other Latin American countries are paying attention, says Meza, who recently presented his findings in Guatemala.

Environmental Exposures

Nestled in the middle of a basin surrounded by mountains, Mexico City is one of the most polluted cities in Latin America. Ozone and particulate matter levels exceed World Health Organization recommendations by as much as two-thirds, according to Jose Luis Texcalac-Sangrador of the National Institute of Public Health of Mexico.

U-M SPH Associate Professor Marie O’Neill is working with Texcalac-Sangrador and others to assess the impact of air pollution and other environmental exposures, among them noise and temperature extremes, on preterm birth—a costly and long-term burden, given that children born pre-term frequently have poor lung development and cognitive functioning.

With SPH Professor Karen Peterson and colleagues in Mexico, O’Neill is also examining environmental exposures through the collaborative study ELEMENT, now more than 20 years old. The ELEMENT scientists are tracking environmental exposures in women before and during pregnancy and gauging the impact of those exposures on infants and children—including cognitive development and risk for obesity and metabolic syndrome.

Foremost among the environmental toxicants they’re studying is lead, which in Mexico comes chiefly from ceramics and paint, and—prior to 1997—leaded gasoline. One in three people in rural Mexico is born with lead poisoning.

The team’s findings suggest that lead is stored in the bones and affects health at key moments in the lifecourse, including pregnancy, early childhood, and adolescence. Current U.S. Centers for Disease Control and Prevention guidelines for lead exposures during pregnancy come from the ELEMENT study.

Tobacco Use

His two-year tenure as a postdoctoral fellow at U-M SPH convinced Tonatiuh Barrientos-Gutiérrez of Mexico’s National Institute of Public Health that if real advances are to be made in the fight against chronic disease, tructural interventions are necessary. Tobacco is a prime example. “We were very unsuccessful for many years in trying to control the way in which people were smoking,” he recalls, “because we were trying to change behaviors and not the environment.”

After Mexico signed the World Health Organization Framework Convention on Tobacco Control in 2004, the country began introducing more aggressive tobacco control policies, such as higher prices for tobacco products, health warning labels on tobacco packaging, bans on smoking ads, and smoke-free environments. Smoking prevalence and intensity rates have both dropped as a result.

But it’s not enough, according to U-M SPH alumna and Assistant Professor of Epidemiology Nancy Fleischer, PhD ’10, who is working with scientists at the University of South Carolina and Mexico’s National Institute of Public Health to examine social environments in seven Mexican cities, including the capital. The researchers hope to learn how economic deprivation, social norms, social cohesion, and violence affect smoking cessation and quit behaviors. Fleischer is also collaborating with SPH colleague Marie O’Neill to understand the role of social context in adverse-pregnancy outcomes in Mexico City. Findings from their work could lead to the kinds of structural interventions Barrientos-Gutiérrez sees as essential to lowering Mexico’s chronic disease burden.

Maternal and Child Health

Between 2000 and 2006, the Mexican government—with major input from U-M SPH alumnus Julio Frenk, then minister of health (see "We have a lot to learn from each other," below)—launched the country’s first comprehensive health insurance program, Seguro Popular. Suddenly millions of previously uninsured Mexicans had access to care, among them pregnant women, many from low-income communities. No one had been taking care of these women,” says physician Felipe Vadillo-Ortega, an adjunct professor of environmental health sciences at U-M SPH and faculty member at the Universidad Nacional Autónoma de Mexico.

Over the past four years, Vadillo-Ortega, in collaboration with Michigan’s Marie O’Neill and others, ran a study at a Mexico City hospital where participating women received free prenatal care as many as eight times during their pregnancies—up to four visits more than stipulated by Seguro Popular. The approximately 900 women in the study saw specialists in obstetrics and gynecology, nutrition, and fetal medicine. Vadillo-Ortega describes the study as a model of care that may reduce complications like preterm labor, preeclampsia, and gestational diabetes, and improve birth outcomes.

Marisol Castillo-Castrejón, a Mexican nutritionist and U-M SPH postdoctoral fellow, is contributing to the study by exploring associations between environmental factors—including green spaces and food environments—and ifestyle patterns and outcomes in pregnant women who live in highly populated urban areas. A better understanding of such factors may inspire interventions to improve health and reduce health care costs. The researchers also hope their findings will contribute to new national regulations for prenatal care and increased access to and usage of green spaces in Mexico City. 

Infectious Disease

Although infectious diseases may have diminished as a result of the epidemiologic transition, they haven’t gone away. At scenic Xochimilco, the last vestige of the pristine lake that once surrounded Mexico City and is now fed by wastewater from the capital, scientists are on the lookout for pathogens like enterovirus and rotavirus. Health officials are worried, as well, that with climate change, which has already led to increased downpours and flooding during Mexico’s rainy season, diseases like Dengue fever and Zika may reach the capital.

An hour north of Mexico City, in a 400- square-mile valley irrigated by untreated wastewater from Mexico City, officials are concerned about the incidence of diarrheal disease and the growing presence of enteric pathogens and antibiotic resistance in the area. A multidisciplinary team of scientists, among them U-M SPH epidemiologists Joseph Eisenberg and Rafael Meza, is conducting a longitudinal study of the health impacts of a new $782 million wastewater treatment plant, which opened this year in the valley. Because some communities in the area now receive treated wastewater and others receive untreated wastewater, Eisenberg and Meza have an unprecedented opportunity to evaluate the plant’s impact on the incidence of diarrheal diseases in children and on the presence of enteric pathogens and antibiotic resistance in communities across the valley.

The issue is not as simple as it may seem. “As clean water becomes an increasingly scarce resource, the value of wastewater cannot be ignored,” says Mexican geologist Christina Siebe of the Universidad Nacional Autónoma de México, who is collaborating on the study. Thanks to growing urbanization, there’s more wastewater worldwide than ever before, and little if any of it is treated, Eisenberg explains, so this research has global ramifications. Findings from previous research in the valley informed the original guidelines for wastewater re-use set by the World Health Organization in 2006 and will inform a planned revision of those guidelines.

--Leslie Stainton