Climate and Cancer
In my previous blog post, I discussed the connection between cancer and cell phones. It was brought to my attention (by Dr. Islas) that I could take this data one step further to determine how heat impacts cancer. Here is a review of my previous conclusions...
(1) Cell phones emit what we call non-ionizing radiation which has enough energy to make molecules vibrate, but not enough to cause the damage we see with UV rays (formation of thymidine dimers) or through the higher energy ionizing radiation (X-Rays and Gamma Rays) that can break chemical bonds and remove electrons from atoms. This means that the energy emitted by cell phones is not capable of causing cancer via direct DNA damage.
(2) I discussed the theory that the energy released by cellphones is capable of physically heating up the cells in the exposed tisssue, which then leads to heat induced DNA damage and then causes cancer. I showed evidence that heat can cause DNA damage. This was shown by Yan. et. al in their experiment that studied the presence of a histone variant (H2AX) that is phosphorylated in the event of a double strand break (DSB). They proved that heated cells had more phosphorylated H2AX and therefore more DSBs; I took this information further to say that if a hypothetical phone was created that could heat up exposed cells enough to induce these DSBs that there could be validity behind the argument that "cell phones" can cause cancer.
This is where I will begin this new blog post! Many of us can attest to the fact that sometimes our phones do heat up while we use them during the day, so it really isn't too much of a stretch to suggest that our phones could be heating up our tissues and causing DSBs on a regular basis! I have done some investigating, and I believe that this data debunks the idea that tissue heating from cell phones can cause cancer.
The Data:
I searched far and wide for data that would give us an appropriate lens through which to study this problem. To analyze the claim that heat causes cancer I decided to look again at a populations level to determine if some areas had different incidence of cancer that could be correlated to temperature. Here in Santa Clara, we are fortunate enough to have many days of beautiful warm weather! However if heating up body tissue causes cancer areas like Santa Clara that are exposed to incredibly warm temperatures for a regular and extended period of time should have much higher rates of cancer!
In the figure below I have chosen to compare 4 different states in terms of their average annual temperatures and average incidences of cancer. For both sets of data, I included every year between 2000 and 2010. North Dakota and Maine had the lowest average temperature annually (which means they can represent the coolest states where we expect to see very low rates of cancer) while Louisiana and Florida had the highest average temperature annually (in these "warm" states we expect to see very high incidences of cancer). Additionally, I chose to look at all cancers for both men and women without including race in the mix. I felt that this was the best way to sample for cancers based on environmental temperature exposure (remember we are not talking about heating from direct sunlight here, just the physical temperature you are exposed to).
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| Average Temperature and Cancer Incidences between 2000–2010 for Warmest and Coolest States. The average temperatures of the two warmest and coolest states in the continental US were determined using data available per state for the annual temperature averages on National Climate Center Data. The average incidence of all cancers (both male and female) for each state per year was gathered from the CDC's United States Cancer Statistics Database using the value for all races. All data was then compiled and standard deviations were calculated from the various noted averages.
As you can see from the data above there is no clear link between the environmental temperature and incidence of cancer. I have chosen to show the top 2 warmest and coolest states and their relative cancer incidences, however I actually compiled the data for the top 5 warmest and coolest continental US states (and would be happy to share the data with anyone who asks!) The data showed much of the same trend. The temperatures of each location on average remain generally stable (as you can see by the very small error bars) which means that these are good states to choose to compare to one another in terms of temperature. The incidences of cancer however are highly variant. This could be for a few different reasons...
1) Heat may have nothing (or very little) to do with cancer, which debunks the idea that the heat from your cell-phone is putting you in peril on a daily basis! I believe that this data is convincing because as I searched for data, the CDC website also had an interactive map that displayed the national incidences of caner by state. Amazingly Maine is always has one of the highest incidenes of cancer even though it is one of the coolest states (CDC map).
2) Cancer diagnosis, at least on a national level, does not catch every case of cancer. It is likely that socioeconomic status (which I will be discussing in my next blog post) could make reporting cancers much less accurate than things like the weather. As you can see the incidence values have very large error bars. This skews the dataset and makes it much harder to make comparisons.
Concluding Thoughts
While in my last post I suggested that a cell phone capable of heating body tissue could give some merit to the claim that cell phones can cause cancer, this populations study shows that this is a weak argument. There is no data that correlates an increased exposure to high temperatures to a higher risk or incidence of developing cancer.
The other top states that I have data for are as follows... Cold States: Minnesota Wyoming Vermont Warm States: Arizona Texas Mississippi References: |
"Climate at a Glance." National Climatic Data Center (NCDC). National Oceanic and Atmospheric Administration, n.d. Web. 12 May 2014.
