Long ago, when SSC had an article about the altitude/obesity thing, a friend and I looked more closely at the data. I concluded that it seems like the bulk of the effect is explainable by selection effect, since there are very few people who live above a few thousand feet elevation, and they’re probably disproportionately upper class and active. See https://slatestarcodex.com/2016/12/11/open-thread-64-5/#comment-443619 (and the original post at https://slatestarcodex.com/2016/12/05/thin-air/). I’m serious about these selection effects—the data linked in my comment includes BMI values up to 3km or 9,800 feet above sea level. I don’t think there are 10,000 Americans living at that elevation total, and they almost all live in towns that primarily exist to serve wilderness recreation.
When Scott more recently posted about this hypothesis in one of the ACX open threads, one of the SMTM authors answered some questions in the comments. The mechanism tying elevation to pollution is allegedly that elevation is a proxy for how upstream you are in the water cycle, since water will accumulate toxins from the ground or being pumped into the water as it goes. To me, this seems like an extremely loose association. The relationship will depend strongly on how many pollutants are in the local area and how quickly the water loses elevation. Also, where people get their water from may not reflect exactly where they live: Consider Dillon reservoir (https://en.wikipedia.org/wiki/Dillon_Reservoir) at 9,100 feet. This water serves people in Denver, 4,000 feet below, after a fairly direct route through a tunnel and then into the Southe Platte River. The people who live near the reservoir get their water from the Green Mountain Reservoir (https://en.wikipedia.org/wiki/Green_Mountain_Reservoir) over 1,000 feet lower. And both reservoirs are filled largely from snowmelt, with the former being surrounded by generally higher mountains. And there’s clearly a lot of other factors that are visible in the obesity map at the top of Scott’s original post other than elevation—for example, there’s clearly a large drop in obesity from Kansas to Colorado, even though the state border is in a flat area 100 miles from the Rockies. You can also see large differences between New England, the upper Midwest, and the South, despite all those places being the exact same elevation.
Given the exceedingly noisy part that pollution must play in this story, and the extreme selection effects that are required to see a clear relationship between elevation and obesity, I think the latter is a much more likely explanation of the link than pollution.
The mechanism tying elevation to pollution is allegedly that elevation is a proxy for how upstream you are in the water cycle, since water will accumulate toxins from the ground or being pumped into the water as it goes. To me, this seems like an extremely loose association.
I agree, but moreover it looks like it should be an easy theory to test. My guess is that there are basically three routes for contaminants to enter our body and make us fat. The chemicals could be in the air, the water, or our food. If the SMTM authors believe that it’s in our water, then drinking distilled or purified water should make us thinner. Do we have any evidence of this?
When I looked into it, you could see an effect on birthweight for babies born to mothers in high altitudes vs their lower-altitude siblings, and vice versa, which suggests to me something non-genetic is going on. And the effect of altitude on birth weight held up in countries where altitude was associated with both lower and higher income (although that wasn’t the sibling study), which pushes against and doesn’t eliminate income effects.
(I’m not actually sure if e.g. median income is positively associated with elevation in the US, since a bunch of those people are “ski bums” working a series of seasonal jobs at ski resorts, white water rafting companies, etc. I used the word class because I think those people are still disproportionately drawing from upper-class cultures and probably have high education on average, and there are definitely a lot of rich people hanging around as well, and the latter are more likely to live closer to the resorts. Mean income is definitely higher in those areas, though.)
That’s a really neat set of data in that blog post which I will have to go over in more detail later. The effect size doesn’t seem to be that large to me, but maybe I don’t have a good intuition for birth weight; 100 g = 0.2 pounds corresponds to 4% of the low range of what is considered healthy in European babies. And that’s over a fairly wide elevation range of 3,300 feet. So I would be surprised if that could explain the very large difference in adult average BMI, but I could also be totally wrong about how fetal weight translates to adult weight. Given the limitations of “controlling for observables” I’m also still leaning towards selection effects, but the close linear relationship does cast doubt on that idea. I think it casts doubt on the pollution hypothesis too, FWIW, since there’s no way that’s cleanly linear, and it probably fits better with hypoxia but still not perfectly, since air pressure decreases sublinearly with elevation.
The mechanism tying elevation to pollution is allegedly that elevation is a proxy for how upstream you are in the water cycle, since water will accumulate toxins from the ground or being pumped into the water as it goes. [...] And there’s clearly a lot of other factors that are visible in the obesity map at the top of Scott’s original post other than elevation—for example, there’s clearly a large drop in obesity from Kansas to Colorado, even though the state border is in a flat area 100 miles from the Rockies.
Eastern Colorado is topologically very similar to Kansas and I suspect they get more water from wells than the (much more populous) middle of the state.
Long ago, when SSC had an article about the altitude/obesity thing, a friend and I looked more closely at the data. I concluded that it seems like the bulk of the effect is explainable by selection effect, since there are very few people who live above a few thousand feet elevation, and they’re probably disproportionately upper class and active. See https://slatestarcodex.com/2016/12/11/open-thread-64-5/#comment-443619 (and the original post at https://slatestarcodex.com/2016/12/05/thin-air/). I’m serious about these selection effects—the data linked in my comment includes BMI values up to 3km or 9,800 feet above sea level. I don’t think there are 10,000 Americans living at that elevation total, and they almost all live in towns that primarily exist to serve wilderness recreation.
When Scott more recently posted about this hypothesis in one of the ACX open threads, one of the SMTM authors answered some questions in the comments. The mechanism tying elevation to pollution is allegedly that elevation is a proxy for how upstream you are in the water cycle, since water will accumulate toxins from the ground or being pumped into the water as it goes. To me, this seems like an extremely loose association. The relationship will depend strongly on how many pollutants are in the local area and how quickly the water loses elevation. Also, where people get their water from may not reflect exactly where they live: Consider Dillon reservoir (https://en.wikipedia.org/wiki/Dillon_Reservoir) at 9,100 feet. This water serves people in Denver, 4,000 feet below, after a fairly direct route through a tunnel and then into the Southe Platte River. The people who live near the reservoir get their water from the Green Mountain Reservoir (https://en.wikipedia.org/wiki/Green_Mountain_Reservoir) over 1,000 feet lower. And both reservoirs are filled largely from snowmelt, with the former being surrounded by generally higher mountains. And there’s clearly a lot of other factors that are visible in the obesity map at the top of Scott’s original post other than elevation—for example, there’s clearly a large drop in obesity from Kansas to Colorado, even though the state border is in a flat area 100 miles from the Rockies. You can also see large differences between New England, the upper Midwest, and the South, despite all those places being the exact same elevation.
Given the exceedingly noisy part that pollution must play in this story, and the extreme selection effects that are required to see a clear relationship between elevation and obesity, I think the latter is a much more likely explanation of the link than pollution.
I agree, but moreover it looks like it should be an easy theory to test. My guess is that there are basically three routes for contaminants to enter our body and make us fat. The chemicals could be in the air, the water, or our food. If the SMTM authors believe that it’s in our water, then drinking distilled or purified water should make us thinner. Do we have any evidence of this?
I have no idea, although I expect any such effect to be a very long-term thing and thus tricky to design and measure.
When I looked into it, you could see an effect on birthweight for babies born to mothers in high altitudes vs their lower-altitude siblings, and vice versa, which suggests to me something non-genetic is going on. And the effect of altitude on birth weight held up in countries where altitude was associated with both lower and higher income (although that wasn’t the sibling study), which pushes against and doesn’t eliminate income effects.
(I’m not actually sure if e.g. median income is positively associated with elevation in the US, since a bunch of those people are “ski bums” working a series of seasonal jobs at ski resorts, white water rafting companies, etc. I used the word class because I think those people are still disproportionately drawing from upper-class cultures and probably have high education on average, and there are definitely a lot of rich people hanging around as well, and the latter are more likely to live closer to the resorts. Mean income is definitely higher in those areas, though.)
That’s a really neat set of data in that blog post which I will have to go over in more detail later. The effect size doesn’t seem to be that large to me, but maybe I don’t have a good intuition for birth weight; 100 g = 0.2 pounds corresponds to 4% of the low range of what is considered healthy in European babies. And that’s over a fairly wide elevation range of 3,300 feet. So I would be surprised if that could explain the very large difference in adult average BMI, but I could also be totally wrong about how fetal weight translates to adult weight. Given the limitations of “controlling for observables” I’m also still leaning towards selection effects, but the close linear relationship does cast doubt on that idea. I think it casts doubt on the pollution hypothesis too, FWIW, since there’s no way that’s cleanly linear, and it probably fits better with hypoxia but still not perfectly, since air pressure decreases sublinearly with elevation.
Isn’t this specific point evidence in favor of SMTM’s hypothesis? Eastern Colorado and Kansas are at similar elevations, but Colorado gets most of its water from rivers that start in Colorado and Kansas gets most of its water from an aquifer (https://geokansas.ku.edu/water-kansas). SMTM suspects aquifers are more contaminated (with lithium?) (https://slimemoldtimemold.com/2021/10/19/a-chemical-hunger-interlude-h-well-well-well/).
I found this,https://www.cohealthdata.dphe.state.co.us/chd/Resources/briefs/Obesity.pdf which shows the east part of Co. as more obese. (Not sure how it compares to Kansas)
Eastern Colorado is topologically very similar to Kansas and I suspect they get more water from wells than the (much more populous) middle of the state.