Monday, May 7, 2012

The 2012 Arch Intern Med red meat-mortality study: The “protective” effect of smoking

In a previous post () I used WarpPLS () to analyze the model below, using data reported in a recent study looking at the relationship between red meat consumption and mortality. The model below shows the different paths through which smoking influences mortality, highlighted in red. The study was not about smoking, but data was collected on that variable; hence this post.

When one builds a model like the one above, and tests it with empirical data, the person does something similar to what a physicist would do. The model is a graphical representation of a complex equation, which embodies the beliefs of the modeler. WarpPLS builds the complex equation automatically for the user, who would otherwise have to write it down using mathematical symbols.

The results yielded by the complex equation, partly in the form of coefficients of association for direct relationships (the betas next to the arrows), have a meaning. Some may look odd, and require novel interpretations, much in the same way that odd results from an equation describing planetary motions may have led to the development of the theory of black holes.

Nothing is actually "proven" by the results. They are part of the long and painstaking process we call "research". To advance new knowledge, one needs a lot more than a single study. Darwin's theory of evolution is still being tested. Based on various tests and partial refutations, it has itself evolved a great deal since its original formulation.

One set of results that are generated based on the model above by WarpPLS, in addition to coefficients for direct relationships, are coefficients of association called "total effects". They aggregate all of the effects, via multiple paths, between each pair of variables. Below is a table of total effects, with the total effects of smoking on diabetes incidence and overall mortality highlighted in red.

As you can see, the total effects of smoking on diabetes incidence and overall mortality are negative, but small enough to be considered insignificant. This is interesting, because smoking is definitely not health-promoting. Among hunter-gatherers, who often smoke tobacco, it increases the incidence of various types of cancer (). And it may be at the source of many of the health problems suggested by analyses on the China Study II data ().

So what are these results telling us? They tell us that smoking has an intermediate protective effect, very likely associated with its anorexic effect. Smoking is an appetite suppressor. Its total effect on food intake is negative, and strong. As we can see from the table of total effects, just below the two numbers highlighted in red, the total effect of smoking on food intake is -0.356.

Still, it looks like smoking is nearly as bad as overeating to the point of becoming obese (), in terms of its overall effect on health. Otherwise we would see a positive total effect on overall mortality of comparable strength to the negative total effect on food intake.

Smoking may make one eat less, but it ends up hastening one’s demise through different paths.


john said...

I believe smoking [nicotine] increases FFAs and decreases intracellular Ca.

Dr. B G said...

There is a benefit v. cost with smoking... Cigarettes are a source of heavy metals (cadmium, etc) and oxidative factors, however the nicotine activates the PSNS and cholinergic nervous system which meditation and exercise both can affect in positive ways.

What do the smoking in Europe, France and countries that consume adequate saturated fat look like (v. China, America), I wonder...??

Activation of the Cholinergic Antiinflammatory Pathway Ameliorates Obesity-Induced Inflammation and Insulin Resistance
Endocrinology, March 2011, 152(3):0000–0000.

David Isaak said...

What an entertaining analysis!

I echo what Dr BG says, however. Nicotine has a number of beneficial effects on the nervous system--cognitive function. It also lowers the risk of Parkinson's disease and seems to ameliorate some of the smptoms of schizophrenia. Nicotine-related pharmaceuticals are a hot research area.

I think that the relationship between smoking and weight gain is more complicated than simply appetite supression. Smoking also speeds the passage of food through the body; constipation is one of the seldom-mentioned side-effects of quitting. Smoking is also notorious for raising blood pressure; it was a doctor who pointed out to me that this in itself burns more calories--though that can't be recommended as a weight-loss methodology!

Ned Kock said...

Hello gentleman and lady G. So it seems like we have a consensus eh?

But let’s not forget that nicotine’s effect is mediated by stress hormones.

Intense exercise has a similar effect, but also leads to a very sharp increase in GH levels:

The effect of nicotine on memory is mediated by cortisol. We achieved better results with, believe it or not, a snake-screen:

BJJ and Paleo Diet Blog said...

That is interesting that smoking can actually improve diabetics health. Imagine if they just followed the paleo diet instead.

DePaw said...

Dr BG,

These heavy metals are ADDED to the tobacco.

Just look at what's allowed:

The plants will also get strayed with chemicals as others are, sure broccoli would test possible for some nasty stuff too.

American Spirit tobacco is addictive-free.

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Sylvia said...

This is so rude statistic, i'm just happy because i love more fresh and cooked vegetables

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