Celebrating 20 years of progress with the Mexican Teachers’ Cohort

Twenty years ago, researchers in Mexico set out to answer a question that could not be answered retrospectively: ‘How do lifestyle, reproductive and environmental factors shape women’s risk of cancer and other chronic diseases over time?’

“The only way to do that is to start off with a group of people who are free of the disease and wait until that disease occurs,” says Dr Martin Lajous, who directs the Mexican Teachers’ Cohort (MTC), now one of the largest long-term health studies in Latin America.

Since 2006, the MTC cohort has followed more than 115,000 women working in Mexico’s public education system, generating evidence on breast cancer, cardiometabolic disease, smoking, sugar-sweetened beverages, alcohol and other risk factors.

But building the cohort was only the first challenge. For years, the team worked to solve a persistent problem – how to identify new cancer cases in a country without a national cancer registry. The turning point came in 2019 when the problem was finally solved and, as Dr Lajous puts it, the MTC moved from being “a promise of a cancer cohort to a realisation of a cancer cohort”.

While there has been great change around the world, and in Mexico over the last 2 decades, from evolving technology to changing eating habits, collaboration has remained central to the mission of the MTC.

Long term partners

Funding to establish the Mexican Teachers’ Cohort began in 2006. Since then, the MTC has followed more than 115,000 women working in Mexico’s public education system. It generates evidence on breast cancer, heart disease, smoking, sugar-sweetened beverages, alcohol and other risk factors.

Collaboration has remained central to the mission of the MTC. “None of this would have been possible without AICR and WCRF, you believed in us,” says Dr Lajous. “And we are forever grateful for this sustained support.”

The partnership between the American Institute for Cancer Research, WCRF and MTC remains strong and ongoing. In 2020, AICR funded a grant for Dr Lajous to study lifestyle and breast cancer risk in a prospective study of Mexican women. In 2026, AICR funded a grant for Dr Lajous to study fibre, gut microbiome and colorectal cancer risk in a prospective study of Mexican women.

In May 2026, the WCRF International bursary helped Dr Lajous’ colleague Dr Liliana Gómez Flores Ramos, PhD, to attend the International Agency for Research on Cancer (IARC) conference in Lyon, France. At the IARC conference, she presented work on alcohol consumption and breast cancer from the MTC.

The story so far

The idea for the Mexican Teachers’ Cohort grew out of a 2004 case-control study on carbohydrates and breast cancer, led by Dr Isabel Romieu, Dr Walter Willett and Dr Mauricio Hernández. The study attracted wide attention, and inspired by international studies using teachers, sparked the idea for a prospective cohort based in Mexico.

Dr Lajous, who was based at the Harvard School of Public Health at the time, was invited to be part of the team setting up the project.

“We invited more than 115,000 women, working in the public education system in Mexico to provide us with details on their health conditions, but also on their lifestyle,” says Dr Lajous. “It was built with the intention of following up over time to be able to compare these lifestyle factors, or reproductive factors, in individuals who ended up having, for instance, breast cancer and those women who did not.”

From a promise to a realisation

ESMaestras researchers and operational staff at the Annual Liaison Meeting held on December 6, 2019, at the facilities of the Mexican Health Foundation (FUNSALUD).

When the cohort was first established, the program was able to collect baseline data. (such as age, menopause and smoking status, and BMI) and the participants have been completing questionnaires approximately every 4-6 years.

“But, in order to have a cancer cohort, you have to demonstrate that you can actually identify individuals who develop the disease,” says Dr Lajous. “And this element is what really took time to develop, making the primary challenge ascertaining incident cancer cases without a national cancer registry.”

By collaborating with different institutions in Mexico, the MTC were able to verify national IDs and have achieved approximately 97% ID coverage within the cohort. The national ID numbers then enabled cross-linkage with national mortality registries, cancer registries and health utilisation databases.

By 2019, they had developed a multi-source strategy to identify cancer cases using health utilisation databases (discharge data, consultations, medication use) from major healthcare providers.

“We dedicated three years to develop the method and convince the stakeholders, and to get everyone together, which took a lot of conviction, and then we finally got it done,” says Dr Lajous.“That’s when we went from being a promise of a cancer cohort to a realisation of a cancer cohort.”

Key milestones

An example of the questionnaire for participants, originally circulated by post.

Aside from officially becoming a cancer cohort in 2019, key milestones include findings that have had implications for prevention and public health policy.

Highlights include data on diabetes and weight gain that informed Mexico’s sugar-sweetened beverages tax. “Mexico has led efforts to change the dietary environment and reduce the consumption of sugar, sweetened beverages,” says Dr Lajous. “So, we conducted analysis on sugar-sweetened beverage intake and diabetes and also weight gain, which I think has been used by policy makers.”

The cohort has also produced some important work on smoking. “You may presume that we already know about the link between tobacco and cancer,” says Dr Lajous. “That may be so, but the pattern of tobacco smoking in Mexico, and particularly among women in Mexico, is one of occasional or very low consumption.

“There is a perception that if you only smoke a cigarette a week, it’s fine. However, we showed with the Mexican Teacher’s Cohort that even very low consumption of tobacco was associated with death.”

In recent years, external groups have begun seeking data from the MTC, shifting internal perception from a theoretical project to a strategic asset, something that Dr Lajous is proud of. “For the past 20 years, I’ve been reaching out to people to let them know how important the cohort is, how key this resource is, how they all should be proud of it. And now the dial has shifted, and institutions have started reaching out to us to collaborate, but it took time.”

Engagement and building trust

Teachers offered two advantages that made a long-term study feasible. Many were already used to completing written evaluations through an economic incentive programme, and their employment stability, healthcare access and pension system made it easier for researchers to remain in contact over many years. But the cohort’s longevity has depended on more than the suitability of teachers as a study population, it has also depended on trust.

“You must have a participant-centered approach, in the sense that if we promise something to the participants, be sure that you deliver that,” says Dr Lajous.

A key challenge for the team over time has been maintaining this engagement as teachers retire and communication has evolved from paper to electronic.

To ensure contact is kept consistent, the MTC plan monthly webinars, a well-attended series on health topics for all teachers, not just those who are part of the study. The team has also moved to home visits to collect data in-person for older, less tech-savvy participants. And, to ensure community building, created state-specific Facebook groups for participants.

Importantly, Dr Lajous stresses a two-way dialogue with the cohort. Feedback from teachers has helped shape the research agenda, leading to studies on stress and Adverse Childhood Experiences (ACEs). “One thing we’re always pushing for is that we keep our ears open to their concerns,” he says.

Lessons learned from the Mexican Teachers’ Cohort

Dr Martin Lajous speaking to the audience at the 20th anniversary event for the Mexican Teachers’ Cohort.

A lesson for Dr Lajous over the last 2 decades of setting up such a large-scale and long-term cohort is patience. “It’s a marathon in the sense that it requires consistency over time,” he says. “Understanding that this is a long-term investment and that you need to be patient. Sometimes things are not going great, but you just need to keep moving.”

People are at the heart of the project. Fostering a dedicated team and using international partnerships to build leverage and demonstrate value has been essential to the MTC. Dr Lajous also notes the importance of incorporating young investigators into the cohort and making them feel invested, so that the programme can be sustained over a long period of time.

“We are a relatively small team and collaboration with people outside of Mexico is important for us,” says Dr Lajous. “It gives us leverage in Mexico and also because it articulates that what we’re doing is important, and people elsewhere are seeing the value in the work that we’re doing.”

Future research

As the cohort enters its third decade, its research questions are changing with its participants.

“We want to understand the intersection between ageing, cognitive health, and cancer. So now we have a grant where we are going to visit 15,000-17,000 participants at their homes to perform in-depth cognitive assessments,” says Dr Lajous.

The team also plans to expand their work into environmental exposures including plastics, light at night, and climate-mediated events.

“And for me, the most salient cancer-related problem right now is colorectal cancer, which is increasing much more dramatically than other cancers. It’s currently the leading cause of cancer mortality in Mexico but we have very limited strategies for prevention and control of the disease.”

Reflecting on the last 20 years, Dr Lajous says, “I’m most proud of how this project has changed people’s lives and will potentially change a lot more people’s lives.”

Looking back, the cohort’s greatest achievement may be exactly what it set out to create – evidence rooted in real lives, sustained by trust, with the power to inform future generations on cancer prevention.