Today was a lovely day. The weather was perfect, a good day in lab, a good run, a delicious veggie burger, a good beer. Life was pretty much perfect as I sat down in a mood to blog.
...and then I read this paper. And it was like this:
(You know, if only they could have told it to me in a GOOD way...)
There are some papers that you finish reading, and you think to yourself "yup, we're all screwed". I think I have to go find a heartwarming paper about curing cancer now to make myself feel better.
See, first first hand smoke came for your lungs. Then it came for your throat. Then SECOND hand smoke came for your lungs.
...and then they both came after your SPERM.
Marchetti, et al. "Sidestream tobacco smoke is a male germ cell mutagen" PNAS,
I suppose since this is about sperm it should be a Friday Weird Science, but it's just too depressing...
Oh man, now I'm all down and no one will want to read it. I'll try and be perky about it! HONEST! Bad news in a GOOD way!
So. Smoking. Despite years and years of public campaigns, laws which require cancer warnings, and an increasing amount of social shaming, smoking still happens. In fact, it happens a lot, particularly among men. According to citations from this paper, 35% of men "of reproductive age" (when I think "of reproductive age", I'm thinking 14 and up, but they could be going with 18), smoke. This is not because of rebelliousness or peer pressure (though it may start because of these factors). Nicotine is highly addictive, and inhaled forms of drugs can be very potent reinforcement.
And like most other drugs that feel good, nicotine is really bad for you. Really, really bad. We already know about the lung destruction and the possibility of cancer. But the chemicals from tobacco smoking get into many places other than the lungs via the bloodstream. Basically any place where blood goes. Like your balls.
We already know that smoking itself is bad for your little swimmers. Smoking causes reduced sperm motility, increased DNA damage, and abnormal chromosomes. The DNA damage and chromosomal abnormalities can be transmitted to your offspring, resulting in irreversible genetic changes. Smoking has even been linked with an increased risk of childhood cancer.
Well, that’s smoking and we know smoking’s bad. But what about second hand smoke? Of course, 35% of the adult male population being smokers (that’s not counting the girls), a significant portion of the population will be exposed to second hand smoke. Right now estimates are at about 40% of the population getting significant second smoke exposure (doing things like working in smoky bars, hanging out in said bars, or living with a smoker). And we don’t know as much about the effects of second hand smoke. Secondhand smoke has over 4,000 chemicals in it and at least 50 of those are known carcinogens (but don’t panic yet, there’s a load of things that are carcinogens if taken in the right amounts). We
do know, however, that maternal exposure to second hand smoke can produce problems in the fetus. But that’s the MOM. What about the dad?
To look at this question, the authors of this study took a whole bunch of male mice. They exposed them to mainstream smoke (basically smoking) and sidestream smoke (the main component in secondhand smoke, though they don’t define what exactly “sidestream” smoke means so I’m a little lost there), in varying amounts (either 3 or 16 cigarettes per day). The methods are pretty sketchy on this, if there are supplemental methods I didn’t see any, but if I had to guess how they were getting the mainstream vs sidestream smoke, I’d bet on the mainstream smoke being piped into the cage from the butt end of the cigarette (where your mouth would go), and the sidestream smoke being pumped out from the other end. I can only imagine that that lab smelled LOVELY. They got smoke exposure for 2 weeks and then they took a sperm sample 6 weeks later. This was a sperm sample directly from the epididymus, and the 6 week wait period ensures that these were the mature sperm from the later turnover during the exposure to the smoke.
They looked at the number of mutations in the sperm and calculated the mutation frequency. You can see in the 5th column from the right that the mutation frequency in the sperm was higher in the mainstream smoking conditions (MTS) as well as in the sidestream conditions (STS). Yup, if you smoke OR are exposed to second hand smoke, your sperms are screwy. Or at least, they are MORE screwy than they are normally, you can see there that there is a normal rate of mutation going on here.
So that’s sperm (and we all love sperm), but what about other germ cells? After all,
sperm aren’t the only highly important cell in your body. You’ve also got cells like those found in your bone marrow and the erythrocytes which produce blood cells. These are also germ cells and damage to these could definitely impact your own health further down the line. So they took samples of these from the same mice, and looked at the effects.
You can see here the percent of mutations in the reticulocyte cells (in your bone marrow, on top), and the erythrocytes in your blood (on the bottom). It looks like the lower dose of 3 cigarettes worth of smoke (either mainstream or sidestream) for 2 weeks didn’t have much of an effect here, but the highest dose of 16 cigarettes worth did, resulting in higher levels of mutations relative to normal, though the results weren’t half as striking as those seen in the sperm (nothing is as striking as sperm, amirite?).
The conclusion is that the exposure to secondhand smoke can be damaging to your germ cell lines. It’s not just about smoking exposure anymore. Of course this was only two weeks of exposure, and of course it was in mice, and of course we have no idea if a human (other than one working as a bartender) is generally exposed to 16 cigarettes worth of secondhand smoke in a day. But secondhand smoke could now possibly join the list of other things that screw up your sperm, like chemical mutagens, radiation, air pollution. You know, all those things from daily life. Smoke screws up your sperm, pollution screws up your sperm. LIFE screws up your sperm. Your sperm, they’re just screwed, people. And if your sperm are all mutated…well, in the end so are we. Ouch.
And now I’m going to go read something nice and cheerful about puppies. I think we’d all earned it.
Marchetti, F., Rowan-Carroll, A., Williams, A., Polyzos, A., Berndt-Weis, M., & Yauk, C. (2011). Sidestream tobacco smoke is a male germ cell mutagen Proceedings of the National Academy of Sciences, 108 (31), 12811-12814 DOI: 10.1073/pnas.1106896108