New study reveals smoking’s sneaky role in Alzheimer’s, Parkinson’s, and ALS—and it’s not what you think.

We all know smoking is bad—heart, lungs, cancer—the usual suspects. But what if we told you it might also mess with your brain in ways scientists are just starting to understand?

A groundbreaking study just dropped, and it’s shaking up how we think about tobacco and diseases like Alzheimer’s, Parkinson’s, and ALS. Spoiler: it’s not all bad news, but it is mostly bad.

Here’s what you need to know, minus the medical jargon.

Over 850 Million Smokers = One Giant Problem

Let’s start with the numbers:

  • There are over 850 million tobacco users globally.
  • More than 8 million people die every year from smoking-related illnesses.
  • About 1.2 million of those deaths come from secondhand smoke.

The lungs and heart usually get all the attention, but your brain? It’s been quietly taking hits, too.

Neurodegenerative Diseases: The Big Brain Disruptors

We’re talking about the heavy hitters here:

  • Alzheimer’s Disease (AD)
  • Parkinson’s Disease (PD)
  • Amyotrophic Lateral Sclerosis (ALS)
  • Multiple Sclerosis (MS)
  • Lewy Body Dementia (LBD)

These diseases slowly kill off neurons in the brain and spinal cord, leading to memory loss, movement problems, and mental decline. They’re influenced by a mix of genes and environment—and guess what’s one of the biggest environmental culprits?

Yep. Cigarettes.

Smoking and Your Genes: A Toxic Tag Team

Cigarette smoke isn’t just full of nicotine. It’s a chemical cocktail of over 9,500 compounds, including 79 known cancer-causers. And some of those chemicals are wreaking havoc on your brain by:

  • Causing chronic inflammation
  • Damaging DNA
  • Disrupting blood flow to the brain
  • Lowering levels of important brain proteins like BDNF
  • Interfering with your brain’s immune defenses

All of this weakens your brain’s natural protection against diseases like Alzheimer’s.

The Breakthrough: Smoking’s Genetic Fingerprints on Brain Disease

This study used a powerful tool called Mendelian Randomization (MR)—think of it as a genetic lie detector test—to figure out if smoking really causes brain diseases or if it’s just guilty by association.

Here’s what they found:

Alzheimer’s Disease (AD)

  • More cigarettes = more risk.
  • Starting young or smoking heavily? That raises your AD risk significantly.
  • Even the genes that make you more likely to smoke are linked to Alzheimer’s.

Parkinson’s Disease (PD)

  • Weird twist: Smokers actually have a lower risk of Parkinson’s.
  • Nicotine might be neuroprotective—it boosts dopamine, reduces inflammation, and could slow neuron death.
  • BUT: The protective effect drops off if you keep smoking long-term (thanks, oxidative stress). Quitting helps.

ALS (Amyotrophic Lateral Sclerosis)

  • The data here is murkier.
  • Smoking seems to increase risk, especially for women.
  • Quitting appears to lower your chances.

The Brain-Smoking Connection: It’s Complicated

Smoking has complex effects—sometimes seemingly helpful, mostly harmful. It’s like that friend who occasionally gives good advice but also crashes your car.

Take Alzheimer’s:
Smoking speeds up brain aging and shrinks key areas like the hippocampus—regions you need for memory. Plus, it floods your brain with toxic molecules that promote Alzheimer’s hallmarks: amyloid plaques and tau tangles.

Parkinson’s is the curveball. Nicotine may help some pathways. But keep lighting up, and you’ll likely undo the benefits with brain inflammation and stress.

Quitting Isn’t Just Good—It’s Protective

The best part of this research? It found that quitting smoking (SmkCes) is genetically linked to a lower risk of both Parkinson’s and ALS.

That means it’s not just about not starting—stopping can still help your brain bounce back.

What’s Next?

This study was the first of its kind to map smoking’s genetic role across multiple brain diseases. It used massive genome-wide datasets and a deep-dive into causality—not just correlation.

Still, there are limits:

  • Most data came from people of European descent.
  • Some smoking-related genes weren’t included (they didn’t pass the “strict criteria” test).
  • More research is needed to understand exactly how smoking interacts with our brain pathways.

Bottom Line

Smoking isn’t just bad for your lungs and heart—it may be quietly setting your brain up for decline.

  • If you smoke, quitting might reduce your risk for some neurodegenerative diseases.
  • If you’ve never smoked, now you’ve got even more reason to keep it that way.
  • And if you’re tempted to use the “smoking protects against Parkinson’s” excuse, don’t. The risks far outweigh the benefits.

This study just gave us more evidence to toss in the pile of “Why You Shouldn’t Smoke”—only this time, the target isn’t just your lungs. It’s your mind.

Chen C, Zhu S, Zheng Z, Ding X, Shi W, Xia T, Gu X. A Genome-wide study on the genetic and causal effects of smoking in neurodegeneration. J Transl Med. 2025 Jul 4;23(1):743. doi: 10.1186/s12967-025-06688-9. PMID: 40615926; PMCID: PMC12228318.