Information herein is based on a Scientific American article, originally published on July 2, 2010, and later moved to their blog. See the references below.
An oncologist or surgeon might not notice, but if you mine the data across dozens of hospitals and across time, you find that breast cancer rates are 10% higher on the left than on the right. Now why should that be? Do women nurse on the left more than the right, or perform some other activity asymmetrically, or is the left breast larger than the right, presenting more opportunity for cancer? The answer is none of the above, because the same 10% bias occurs in men. Yes, males are 1% as likely to get breast cancer as females, but there are, nonetheless, enough cases to show a left side bias at the same 10% level with statistical significance. The asymmetry has nothing to do with female chemistry or nursing activities.
Even stranger, other unrelated cancers such as melanoma appear more often on the left side of the body, particularly the trunk, hip, and thigh, areas that are generally shielded from the sun. Why do these non-solar melanomas appear preferentially on the left?
Another point of confusion and concern is the increase in both these cancers from 1980 to 2010. Is there something in the late 20th century that induces cancer at a low level, with a subtle yet significant preference for the left side of the body? It can't be something we eat or breathe, because that would act bilaterally. It must be something external, and acting on the left.
In contrast to the United States and western Europe, Japan has seen no increase in these cancers during the same time period, nor do they see a left side bias. Nothing seems to be attacking the Japanese from the left. We need to look for an environmental agent that is present in the United States and Europe, but not in Japan.
As mentioned in the previous article, our organs are asymmetric. In particular, our heart beats on the left, and it beats a little easier if we lie on our right side, so that the chest is not pressing down on the heart. This is a small effect, hardly noticeable, but on average we spend more hours sleeping on our right side than our left. This sleeping preference is the same the world over, so another variable must be in play. That variable is the bed. Japanese still prefer futons, thin mattresses placed directly on the floor. Western culture has "advanced" to elevated box springs and mattresses, providing a superior level of comfort. Our bed frames are made of metal, and mattresses are typically a sea of connected springs. All this metal acts as an antenna, capturing and amplifying the tv and radio signals that are in the air. Electromagnetic energy is concentrated in a peak that floats 75 centimeters (30 inches) above the mattress, penetrating the left side of a sleeping adult. This happens 8 hours a day, for 30 or 40 years, and apparently it causes cancer at a level that is detectable above the background cancer rates. This connection is supported by epidemiological studies. The combination of FM transmissions and spring mattresses began about 1945, and by 1985 the first batch of sleepers had been exposed to these conditions for 40 years. This is when cancer rates began to rise, showing a left side bias. Furthermore, these additional cancers occur in cities where television and FM radio are prevalent, and citizens sleep on spring mattresses atop metal frames. Perhaps this does not constitute scientific proof, but think about the double blind study that would be necessary for a controlled experiment. Young adults are assigned different bedrooms, shielded from the tv and radio waves of the city, each room generating its own electromagnetic radiation inside at various frequencies and amplitudes. Some rooms have metal spring beds and some rooms have nonmetal beds. Assignments are made at random, and our sleepers cannot tell whether the bed contains metal or not. (We're already in trouble, because you know very well whether you are lying on a spring mattress.) Finally, our human subjects must sleep in these specially constructed rooms for 40 years. Our volunteers can't go away to college, or take a job across the country, or even move into a small apartment with their newly-weds. And don't assume you can get away with a dozen bedrooms, or a hundred. You'll need a large sample, thousands or perhaps tens of thousands, because these cancers are still relatively rare compared to the cancers that occur naturally, and you want some level of statistical significance. Such an experiment is obviously impractical, so we are left with the epidemiological evidence, which is quite compelling nonetheless. The correlation is high, and in this case correlation probably does mean cause and effect. EM radiation really can cause cancer, if it is focused on the same part of your body for several hours a day for 40 years.
If all this is true, then people with situs inversus, where the heart beats on the right, will sleep preferentially on their left side, and contract EM induced breast cancer more often on the right. Can we check for that? Probably not, because we are dividing the number of cases by ten thousand, the prevalence of situs inversus in the general population, and that doesn't leave enough cases to draw any statistically significant conclusions.
In 1991, after I got married, my wife and I decided to sleep on a Select Comfort bed, (now known as a Sleep Number bed), because it was more comfortable and would last longer. 25 years later we are still sleeping on the same bed, satisfied customers to be sure. Are we, without realizing it, reducing our cancer risk? A thin metal frame supports the base of the bed, but the rest of the bed is plastic, the high box that rests atop the metal frame and the air chambers that we sleep on. If the metal frame acts as a weak antenna, much less effective than a spring mattress, the resulting peak is just below the air chamber, and well below our bodies. Good for us. We didn't choose this bed with health considerations in mind, but perhaps we got lucky.
I see commercials for the Sleep Number bed all the time - why don't they claim their bed reduces the risk of breast cancer? That would drive up sales, don't you think? As mentioned above, it is perhaps not proven, so maybe they are reluctant to make the claim, but I see sillier claims every day from weight loss pills, wrinkle creams, male enhancement supplements, copper bracelets, and the like. Use the word "may" in your assertion, and you can get away with just about anything. If I were CEO of Sleep Number or TempurPedic, I'd at least think about it. I don't think it's dishonest, not at all. Consumers should know there is a nontrivial cancer risk that they can easily control by sleeping on air, cloth, or foam. I will probably avoid spring mattresses for the rest of my life.
Speaking of SleepIQ®, the Sleep Number system that monitors your movements throughout the night and documents your sleep quality, I wonder how it reacts to sex? I hope it doesn't view that as restless sleep. Perhaps it knows what that is and sets it to the side. More problematic is the dog. We're sleeping peacefully and she jumps up on the bed, twirls, flops, and pants for 20 minutes. We acknowledge her presence and quickly drop back to sleep, but who knows how SleepIQ registers the panting. After an hour she gets hot between us and jumps off, then sleeps in her own bed for an hour, then jumps back on and starts the cycle again. Well no matter, I don't really want a device monitoring and grading my sleep every night.