Researchers find higher risk of obesity in people living close to sea level
Source: The paper on Association of Elevation, Urbanization, and Ambient Temperature with Obesity Prevalence in the United States. — Telegram illustration/Thinkstock photo
A recent U.S. study found people living in the mountains were four to five times less likely to be obese than those living closer to sea level.
“I made a model to see how much of it was associated with elevation itself. It turned out that the association was stronger than I expected, and more consistent across the full range of elevation,” the study’s lead author J.D. Voss said.
In Newfoundland and Labrador, a sea-level province with the highest rate of obesity in Canada, the finding might sound like a golden ticket to weight loss. However, both Voss, and several experts in St. John’s, suggest that the interaction between altitude and obesity is far more complex.
T.A. Loeffler, a kinesiologist at Memorial University and a well-known mountain climber, felt Voss’ results made intuitive sense.
“You know, as a mountaineer, when I go to altitude, the weight just comes off. Unfortunately, when you come back down, the weight usually goes back on,” she said.
Voss’ study took urbanization, temperature, and behavioural and demographic factors into account.
“But we looked at whether or not there was an association between (obesity and elevation), not whether the association was causative, or the direction of causation,” Voss said.
“In other words, it could be that people who are heavier don’t enjoy living at high altitudes, so they choose to move to lower ones. We just had the basic snapshot in time of the proportion of people who were obese and (where they live).”
This caution was echoed by Dr. Guang Sun, a professor in the faculty of medicine at MUN.
“I think there might be a basis for this, in terms of physiology. But as a scientist, I would be careful to interpret the results because it’s a correlational study,” Sun said.
“(That being said), we know the concentration of oxygen is lower at higher altitudes. In St. John’s the oxygen concentration in the air is about 21 per cent. But (as you travel upwards) it decreases.”
Voss hopes other research will take his findings into account, and look at possible causal factors.
“It could be that cultural values change at high altitude, but my own view is that hypoxia (a deficiency in the amount of oxygen reaching body tissue) should be explored as a cause of weight loss,” Voss said.
Local research on hypoxia
Fabien Basset, an associate professor at MUN, has researched the impact of hypoxia on weight loss. Hypoxia does cause people to lose weight, and affects people who live at high altitude.
He recently published a pilot study that found reduced oxygen levels in the blood set off a chain of events that result in more lipids, or fatty acids, being burned.
“If you lack oxygen, your body will mostly consume glycogen (a form of energy storage) in order to contract your muscles,” Basset said.
“That will deplete your glycogen content in the muscle. As a result, when you are removed from hypoxia, in order to replenish the muscle glycogen you will use lipids.”
Similar to exercise
This passive fat-burning mechanism is actually physiologically similar to what happens during exercise.
“If you run for one hour at a certain intensity, let’s say you’re running the Tely 10, at the end of the Tely 10 your glycogen content will be reduced,” Basset said.
“And then, in what we call post-exercise metabolism, what you are going to do is to use lipids to reproduce the glycogen.”
Though not a replacement for exercise, Basset believes hypoxia could eventually become a reliable tool as part of an obesity reduction program.
“The key is first to have a healthy lifestyle. But maybe hypoxic intervention could be one way to overcome the problem (of weight loss resistance), due to genetic factors, and also the fact that people can’t exercise at a certain intensity because of age, injuries, overweight and so forth,” Basset said.
Voss’ statistical findings seem to support this possible treatment.
“On the scale of medical intervention, (hypoxia) is actually a fairly well-tested intervention in the sense that people are currently living in hypoxic environments, and seem to be surviving just fine,” Voss said.
Potential risks of high altitudes
Voss and Basset say their conclusions should not be taken out of context — despite the present data on obesity rates, higher is not necessarily better.
“Hypoxia could create health risks. There was a paper showing that altitude sickness might be even more common among people who are heavier,” Voss said.
“There was also other data showing association between suicide and high altitude in the United States. Even if there was a metabolic benefit, there could be other harms, like mental health harms or other harms that we don’t even know about from hypoxia itself.”
Basset also cautioned about any extreme lack of oxygen conditions.
“In hypoxia, if you talk to a physician, they are very concerned about what they call sleep apnea.
“In sleep apnea, the hypoxic event is very, very severe. And that leads to a very stressful metabolic response,” Basset said.
The rest of the puzzle
Acknowledging the potential importance of the distance from sea level does not lessen other factors in obesity, such as genetics and lifestyle.
“Different gene sequences, or structures, they make it easier to gain weight, or harder, though either way it’s possible,” Sun said.
“It seems that Newfoundlanders carry some of the genes that put them on the edge, (making it) easier to gain weight. But other factors also contribute, such as the high-fat, high-sugar diet. And personally I think that the reduced physical activity is one of the most important factors in modern society.”
Not that simple
Loeffler also believes weight loss is more complicated than just changing altitude.
“I think, in some ways, the war against obesity has been fought all wrong,” Loeffler said.
“Basically, my wish for everyone in the province is to eat as well as we can, (and do) lots of physical activity, whether that’s walking, hiking, gardening.
“As we’re able to encourage people to lead those kinds of lifestyles, I think we’ll start to see a change in our overall patterns of bodyweight.
“Overall, it’s a useful thing for all of us in the province to aim towards the healthiest lifestyles we can get, and if anyone wants to come to altitude with me, I’m more than happy to take them.”