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For over 30 years, Brazil has run one of the largest studies of a population since birth. 

Every 11 years, all the children born in the city of Pelotas share an unusual fate. Some come to see it as a blessing, others a curse, but either way as the years tick by, the details of their lives will be tracked and recorded. Woven together, they will tell a story about life in Brazil, about health and society and humanity.

For over 30 years, Cesar Victora, professor of epidemiology at the Federal University of Pelotas, and his colleagues have been running one of the largest birth cohort studies to be carried out in a developing country, recruiting every baby born in Pelotas in certain years, then tracking over two thousand different variables about their lives as they grow up.  

When the research started in 1982 with the first cohort, the aim of the research was to better understand the causes and impacts of problems endemic to developing countries at the time – maternal and child health, malnutrition and infectious disease.

Had Pedro Hallal, who has conducted numerous studies on the cohorts, been born just two years later he would have been part of his own experiment. His sister, in fact, is one of his subjects.

Following the babies enrolled in each cohort so far – 1982, 1993 and 2004 – as they grow up has been a huge undertaking. “It’s everyone born in the city in a given year, so it will include singers, it will include sportspeople and it will include a murderer,” Pedro says. “We have had to interview people in the jail. We try to locate them regardless of what they do, because if we lose exactly the complicated ones then there is bias in the study.”

The members of the cohort are asked to come into the lab, where the ground floor is decked out with state-of-the-art body-analysing equipment, as well as rooms for interviews and completion of surveys.

As well as recording the trajectory of each participant’s life from the day they are born, the cohorts also tell a compelling story of a country that has changed unrecognisably in the past 30 years.

“These kids were born in very different Brazils,” Pedro says. “The ones born in ’82 were born into a society that would not have the right to vote, and it was like a developing-country setting.” By 1993, it was “a completely crazy society” dominated by an inflation boom. Inflation was as high as 30 per cent at times, Pedro says. “People would spend their salary as they would get it. So they were born into a very uncertain society. I would probably say it was when Brazil was leading the way in the world in terms of inequality.”

By the time the next cohort arrived in 2004, the country had been transformed. It was a stable society with less extreme inequality. Brazilians could afford to travel abroad for the first time, it was a middle-income country with characteristics of almost a high-income country. “All these things happened in a period of 22 years and all these kids were born into a different phase of this transition.”

2015 marks the start of the next cohort. And this time, as his mentor and former supervisor retires, it will be Pedro who takes the lead, taking his attention away from his work with the academias

Once again, for these babies, things “will be completely different,” he says. “The kids will be born into a country that is part of BRICs, everybody wants to come to Brazil, we are hosting all these big sporting events, it’s got a much better reputation.”

With those changes, the health issues facing the country are also different. Malnutrition and infectious disease have been replaced by chronic diseases, obesity and inactivity. So the team decided to take a new approach. This time the focus will be on one key question: what makes one person active and another not?

“This sounds simple, but it is really the one million dollar question,” Pedro says. “We know a lot about how active people are, we know a lot about the consequences of being active, we know how to intervene and give opportunities to increase access to activity – the one thing we don’t know is why some people are more active than others. Is it how much you see your parents doing it? Is it something biological? Is it something social?”

To answer this, Pedro and his team are turning to technology, purchasing “a ridiculous amount” of accelerometers. These will be used to track the activity of mothers, fathers and the children as they grow up, as well as their brothers and sisters, if they have them.

For the first time, Pedro and his team will also begin the study not on the day the babies are born, but during pregnancy, to see how the mother’s being physically active during pregnancy itself makes a difference to the health of the baby, and whether that affects how active the baby grows up to be. The first pregnant women, due to give birth in 2015, have already been recruited.

Pedro’s team will also carry out a unique piece of research on around 200 of the women to find out the effects of exercising throughout the pregnancy. They will be offered state-of-the-art personal training, and a monitored exercise regime to see how this affects their babies – particularly the chances of premature birth.

“We know that for women, physical activity during pregnancy will improve glucose level, we know it will decrease the likelihood of pre-eclampsia, diabetes and other conditions,” says Pedro. “But there is a hypothesis that physical activity during pregnancy will decrease the likelihood of preterm delivery, which is epidemic in Brazil. What we want to know is: if we give them the best physical exercise training possible, will they be less likely to have a preterm kid?”

Why does all this matter? Because understanding why people are inactive is the best way to get people to change their behaviour in the future, Pedro says. Take smoking, for example. Despite research showing unequivocally the dangers of cigarettes, change was slow. “It took them 50 years to change people’s behaviours,” Pedro says. “Influencing behaviour is a very difficult task. We need to understand more before we can intervene.”

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