## Diabetes and obesity

Update: I made a major error in the algebra of estimating “white diabetes rates” per county. So the last set of correlations was junk. I think fixed the issue. Thanks to “bayesian” who noted that something was off with them.

The CDC provides data on diabetes by county as well as obesity.

Some Correlations:

Diabetes-Obesity = 0.72
Diabetes-Black = 0.65
Diabetes-Latino = -0.14

What’s going on with the last? Latinos, in particular Mexican Americans, are more susceptible to diabetes than whites. So it must be that in counties where there are many Mexican Americans, white have particularly low prevalence of diabetes.

Other correlations:

Diabetes-Obama Vote = -0.01
Diabetes-College Educated = -0.46
Diabetes-Median Household Income = -0.45
Diabetes-Median Home Value = -0.42

I’m struck by the fact that the correlations are higher than for obesity (if you think about it in terms of r-squared, the square of the correlation explaining the variance of Y by X, it’s even more striking). Probably has to do with the fact that only a subset of the obese are diabetic, as diabetes is a more extreme manifestation of morbidity. Let’s control for the % black in a county with partial correlations:

Diabetes-Obesity = 0.63
Diabetes-Obama Vote = -0.28
Diabetes-College Educated = -0.52
Diabetes-Median Household Income = -0.41
Diabetes-Median Home Value = -0.43

Not much change in the correlations really. Also, now there is a modest correlation between political liberalism and lower levels of diabetes now that the black proportion is controlled (the correlation with black proportion controlled for obesity and Obama vote is -0.24, same magnitude and direction).

I also tried to estimate white diabetes prevalence by county. The national data suggest that blacks are 1.7 times more likely to be diabetic, and Latinos 2 times more likely. Obviously there’s going to be some variance for these two groups, so I don’t know how useful this estimate for whites is going to be. But, it should put into stark relief the negative correlation between the proportion of Latinos and white diabetic rates (note: again, Latinos seem to vary quite a bit and there are many counties along the Mexican-American border, as well as on the East Coast, where Latinos are so far deviated from the aggregate risk that I had to dump the data).

Here are some correlations (again, white county proportions are estimates):

White diabetic proportion-White obesity rate (estimate from previous post) = 0.47
White diabetic proportion-College Educated = -0.46
White diabetic proportion-Obama Vote = -0.18
White diabetic proportion-Median Household Income = -0.39
White diabetic proportion-Median Home Value = -0.44

OK, enough with correlations. Maps. Diabetes for all groups:

Now, my estimates for whites:

I think the assumption of an invariant relationship between white and non-white rates (i.e., blacks = 1.7 X whites) is causing problems. The white areas underneath the median suspiciously concentrated in the Black Belt.

So let’s just focus on counties which are 85% or more white:

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1. Razib, are your CDC data mortality due to diabetes or actual diabetes rates. You show that diabetes is negatively correlated with %Hispanic, perhaps this is true if you are looking at mortality. Remember that Hispanics tend to have lower mortality than would be expected based on their SES/SEP or based on their cognitive ability (mortality rates tend to increase when SES/SEP or cognitive ability decreases). The fact that Hispanics have lower mortality than would be expected is called the Hispanic Paradox.

Check out this paper posted on the Nature Precedings website.

http://precedings.nature.com/documents/2862/version/1

It shows that in California Hispanics have lower mortality than would be expected based on their (rather low) cognitive ability (as measured by 7th grade math test scores). The paper postulates that the surprisingly low mortality rates of Hispanics may be due to their CHRM2 allele that codes for higher vagal nerve activity. The vagal nerve may serve as the mind-body link for connecting cognition to better health (the vagal nerve is the body’s own endogenous anti-inflammatory system, thus vagal nerve signaling may prevent atherosclerosis and perhaps some cancers).

2. they’re the proportion of individuals within a county who are diagnosed with diabetes (age adjusted i believe). you can find it here. so no, not mortality. as i said above, it’s probably the fact that latinos are concentrated in the states with the thinnest whites (in contrast with the blacks). since whites are still a majority in many of these counties, you get a cancellation of the effect. there’s no county level data on racial prevalence of diabetes, so i simply estimated it going off standard differences between the ethnic groups (as i said above). this obviously introduces a clear distortion in many areas, where hispanics don’t have diabetes at the rates of their state aggregated expectation (e.g., the hispanics rio grande counties of texas seem to be way healthier than hispanics in the rest of the state).

3. (Razib, feel free to cancel my previous comment)

Why is the white diabetic proportion (per definiton in your comment above) positively correlated (though not too strongly) with the SES markers, when the total correlations (i.e. for whole county population) are negative (as you would expect: higher SES => lower diabetes rate).

I don’t get it – sorry to be so dim, but at least you’ve given me a good humility dose for the day.

4. i made some serious errors in estimating the white diabetes rate. i’m trying to fix that now. will post an update. thanks for bringing the error to my attention!

a