We (hopefully) take a lot of care with our brains. We nourish then, hydrate them, make sure they have a good blood supply, let them get adequate rest (they will use it for tidying up, which is a restful activity if you’re a brain), and maybe even buy them brain-boosting nootropic supplements as a treat.

But a lot of people sabotage their brains, and here’s one of the most surefire ways to do so:

Smoking shrinks the brain, a lot

Ok, so “smoking is bad for the health” is not exactly breaking news, but often its ill effects are put largely down to things such as:

• tar buildup in the lungs
• strain on the cardiovascular system
• carcinogenic effect on cells

Also, the simple fact that it is addictive is often considered somehow responsible for harm to the health. In reality, the addictiveness of nicotine adds to the problem only because it is already bad (as are many of the things that come with it) and people then use more.

It’s not the addiction itself that’s the problem—a substance can be addictive without being deleterious to the health; see caffeine for example.

The difference is, smoking itself is astonishingly bad for the health, while enjoying a little coffee is (for most people) a perfectly healthy thing.

If you’d like to learn more about caffeine before we get back to talking about smoking, check out: Caffeine: Cognitive Enhancer Or Brain-Wrecker?

Bigger evidence for smaller brains

Firstly, why this matters: brain volume loss is an important biomarker of neurodegeneration, that can be easily checked with an MRI scan. Having a physical effect like that, which can be looked at, measured, and pointed to, is a way of knowing that, in a very real world physical material sense, “something wrong is not quite right here”.

It helps stop concerns from being dismissed, and it helps highlight a problem if such was previously being ignored.

Researchers (Dr. Somayeh Meysami et al.) wanted to examine and quantify the effect of smoking on brain atrophy (shrinking), so she and her team looked at the brains of 10,134 participants, of whom 3,292 smokers and 6,842 non-smokers, aged 18–97, using MRI.

In few words: they found that smokers had significantly lower gray and white matter volumes compared to non-smokers, and that especially significant atrophy was found in areas related to Alzheimer’s disease, such as the hippocampus, posterior cingulate, and precuneus, even after adjusting for BMI (which seemed to have a moderate mediating effect overall).

You may be wondering: how much smaller were these brains? And the answer is…

❝Smokers versus non-smokers were compared by gray and white matter volumes normalized to total intracranial volume using a two-tailed t-test. Smokers had lower normalized gray (t = −7.806e+00, p = 6.508e-15) and white matter volumes (t = −7.374e + 00, p = 1.791e-13) compared to non-smokers❞

Read in full: Smoking predicts brain atrophy in 10,134 healthy individuals and is potentially influenced by body mass index

Two things:

1. The “healthy individuals” here is in the sense that they did not have any other clinically-relevant health conditions pre-diagnosed, aside from the ones discussed in the paper (so, brain atrophy, hypertension, diabetes, obesity). It is not suggesting that they were a glowing pinnacle of health; it’s just an accepted convention to express it this way in scientific papers, to disambiguate the “healthy individuals” from those with potentially confounding diseases. For example, it would have complicated the data incredibly if they had included people with lung cancer, or coronary artery disease, or Parkinson’s disease, etc.
2. About those numbers, let’s explain:

For each of those groups we see a t-value and a p-value.

The p-value establishes the probability of getting that result by chance, and therefore indicates the statistical significances of the results. Generally speaking, a p-value under 0.05 is considered statistically significant. Here the p-values are 6.508^-15 and 1.791^-13, which if we express them in full, looks like this: 0.00000000000006508 and 0.0000000000001791. Which suffice it to say, is truly tiny, and therefore incredibly statistically significant. These are some of the lowest p-values this reviewer has ever seen in a paper.

The t-value establishes the number of standard deviations from the norm. In other words, if you take the average difference from the norm (because humans are diverse and we have a lot of very normal difference between our sizes of various organs), then how many multiples of that difference is the difference shown in the study? And in this case, the t-values are -7.806 and -7.374 (this time we can ignore the exponents, since the exponential values are zero, and moving the decimal point zero places in either direction will not change anything, as we can also verify in the complete results table), so that means the brains were more than 7 standard deviations smaller than those of the non-smokers.

One last thing: the above were averages for smokers vs non-smokers, but the effects were dose-dependent, i.e. more smoking = more brain atrophy.

Want to learn more?

You might be interested to know about…

Nicotine Benefits (That We Don’t Recommend)!

Take care!