Living at high altitude may help ward off obesity

Living at high altitude could protect against obesity, according to a study of more than 4 million children across Colombia.

The finding fits with existing evidence that high altitudes help ward off the condition, perhaps because our bodies burn more energy when exposed to lower levels of oxygen. However, most of the research has been on adults.

To understand the potential impact on children, Fernando Lizcano Losada at the University of La Sabana in Chía, Colombia, and his colleagues analysed data on 4.16 million children aged up to 5 years old from 1123 municipalities, compiled by the Colombian Institute of Family Welfare.

The children were separated into four groups relating to the height above sea level at which they lived: up to 1000 metres, 1001 to 2000 metres, 2001 to 3000 metres or above 3000 metres.

In the two lower-altitude regions, around 80 out of every 10,000 children had obesity. However, at altitudes of 2001 to 3000 metres, the prevalence fell to 40 in 10,000.

At altitudes above 3000 metres, the prevalence was higher again: 86 out of 10,000. However, the team says this may be a statistical fluke, as this data set included only seven municipalities and 11,498 people, far fewer than the other three altitude ranges.

“That’s a fair comment,” says David Stensel at Loughborough University in the UK. But he says it would have been more convincing if the team had been able to show a dose-response curve, with obesity rates falling gradually at ever higher altitudes.

Stensel also emphasises that the study is observational, so it doesn’t prove that high altitude prevents obesity. “They have tried to make sure that they have adjusted for the potential confounding factors,” he says. These included measures of poverty and deprivation. But “you can’t account for everything”, says Stensel.

Nevertheless, he says such studies are a starting point. “They show us a relationship, and you then need to really design a bespoke study to investigate that hypothesis on its own.”

Lizcano Losada suggests that people’s metabolisms may run faster at high altitudes, meaning they burn more energy.

That is possible, says Stensel. “There’s a few studies that have shown resting metabolic rate, or basal metabolic rate, increases when you’re at high altitude,” he says. For instance, a study from 1984 found that mountaineers lost more weight at high altitude, in part because fat from their food was burned off or excreted before it was converted into tissue.

More recent studies have suggested that low oxygen levels also contribute to a faster metabolism, and that people at high altitudes have elevated levels of the satiety hormone leptin and lower levels of the hunger hormone ghrelin.

Assuming high altitude really does make obesity less likely, Stensel says it isn’t clear how this knowledge could be of practical use in reducing the condition. But Lizcano Losada argues that different environmental factors may contribute to obesity in different regions, so people might benefit from more tailored advice.