Melanoma: Coincidental Correlation Does Not Prove Causation
melanoma & tanning:
Melanoma: Coincidental Correlation Does Not Prove CausationDoes exposure to sunlight, UVR or a tanning device cause cutaneous malignant melanoma (CMM)?
The answer to this question is extremely important to the indoor tanning industry because, if UVR can be scientifically proven to cause CMM in humans, the survival of the industry is in jeopardy. On the other hand, if the scientific evidence shows that exposure to sunlight, UVR or a tanning device does not cause CMM, there will be no reason for health-conscious individuals to forgo the incontrovertible benefits of UVR exposure-such as maintaining an optimal vitamin D level year-round-in the carefully controlled environment of a professional indoor tanning salon. So, which answer is correct?
Coincidental vs. Causal Correlation
Research reveals that there is only a coincidental correlation-not a causal correlation-between UVR and CMM; therefore, neither sunlight nor a tanning device can be blamed for causing this disease. Think of this in terms of a post hoc ergo propter hoc relationship, in which it is incorrectly believed that one event comes before and, therefore, causes another when, in fact, the two events were examples of coincidental correlation-not cause and effect.
Here are some examples of why coincidental correlation does not prove causation:
* Sleeping with one's shoes on is coincidentally correlated with waking up with a headache. Therefore, going to sleep with your shoes on is the cause of headaches.
* Since the 1950's, both the atmospheric CO2 levels and crime levels have increased sharply. Therefore, atmospheric CO2 causes crime.
However, the logical concept of post hoc ergo propter hoc requires that one event always occur before the other event in order to prove causation. For example, in order to prove exposure to UVR causes CMM, there must be a "molecular signature" of damage to the melanocyte genome each time there is UVR exposure and no such molecular signature has ever been demonstrated. Instead, the sunscreen industry, the dermatology community and vested-interest advocacy groups such as the Skin Cancer Foundation have used a coincidental correlation between sunlight/UVR/tanning devices and CMM to link them together. This is, at best, an example of the post hoc ergo propter hoc logical fallacy in action and, at worst, an example of scientific evidence being manipulated in order to promote a deceptive agenda (i.e. selling products and services, such as sunscreens containing UVA filters).
So, why is exposure to sunlight, UVR or a tanning device blamed for causing CMM given the fact that there is no valid scientific evidence (i.e., no molecular signature,) to support this premise? In order to understand the coincidental correlation that has led to this claim, you must understand how melanocytes function within an epidermal melanin unit (EMU).
Each melanocyte cell produces melanin for approximately 36 keratinocytes; this combination is called an EMU. When the keratinocytes in the EMU sense that UVR is striking the skin, a signal is sent to the melanocyte telling it to produce more melanin. That melanin then will be oxidized by the longer UVR wavelengths to protect the keratinocytes' DNA. This normal and natural response is the genesis of the coincidental correlation that has led to the erroneous belief that UVR causes CMM. However, UVR doesn't damage the melanocyte (which is why there is no "molecular signature" proving causation) but, rather, it sets in motion a coincidental chain of events that can result in CMM. This chain of events begins when the melanocyte is unable to keep up with the demand for melanin by the keratinocytes in its EMU, and another signal is sent that tells the melanocyte (i.e., the "mother" cell) to:
* Detach from the keratinocytes in its EMU;
* Disengage from the basement membrane (and become temporarily free-floating and vulnerable); and
* Divide in order to form an identical "daughter" melanocyte cell.
The normal pattern is for the “mother” melanocyte cell to quit dividing and for both the “mother” and “daughter” melanocyte cells to reattach themselves to the basement membrane and set up a new EMU but, for reasons not yet understood, the “mother” melanocyte cell fails to get the message to quit dividing and becomes a CMM, a continually dividing (immortal) cancer cell. No one knows exactly why this happens, but the most probable theories are based upon the idea that exposure to electromagnetic spectrum wavelengths other than UVR may scramble the signal that tells the “mother” melanocyte cell to quit dividing. These other wavelengths may be:
FM radio broadcast radiation. Hallberg, et al, provided compelling evidence showing that proximity to a FM radio broadcast tower dramatically increased the incidence of CMM.OAS_AD('x96')
High-frequency voltage transients. A recent article showed that teachers in a school with high-frequency voltage transients had 10 times the relative risk (RR) of developing melanoma.
Infrared radiation. Several recent articles have considered the possibility that the heat and the resultant heat shock proteins (especially hsp105), produced by exposure to infrared radiation, play a role in the development of CMM.
A New Theory: Vitamin D Insufficiency
We propose a new theory to explain what allows a melanocyte to transform into a CMM—vitamin D insufficiency. Our belief, which is supported by an increasing body of scientific evidence regarding vitamin D’s role in cellular signaling, is that an insufficient level of vitamin D plays a key role in the process of a melanocyte transforming into a CMM. In this scenario, the environmental factor disrupting the signal telling the “mother” melanocyte cell to quit dividing can only occur when there is an insufficient level of vitamin D. Conversely, when the vitamin D supply is sufficient, the signal will not be disrupted and the process of cell division takes place normally, i.e., without resulting in CMM.
The articles purporting to show that exposure to sunlight, UVR or a tanning device causes CMM all have various forms of bias (i.e., researcher bias, publication bias, recall bias, misclassification bias, methodology bias, sample-size bias, etc.) and these confounding factors make them scientifically invalid. In addition, the studies claiming to show that sunlight, UVR or a tanning device causes CMM all have very small RR values—less than 2.0—when the authors know, or reasonably should know, that a RR of at least 3.0 is required to prove that there is a cause-and-effect relationship between two events. In case they forgot, here are a few quotes to remind them:
“As a general rule of thumb, we are looking for a relative risk of 3.0 or more before accepting a paper for publication.”
–Marcia Angell, editor of the New England Journal Of Medicine
“My basic rule is, if the relative risk isn’t at least 3 or 4, forget it.”
–Robert Temple, director of drug evaluation for the U.S. Food And Drug Administration
“Relative risks of less than 3.0 are considered small and are difficult to interpret. Such increases may be due to chance, coincidence, statistical bias or the effect of confounding factors that are sometimes not evident.”
–Excerpt from a National Cancer Institute publication
To show how statistics can be misleading, let's look at the one that states there was a 55-percent increase in CMM among women using sunbeds. A 55-percent increase means there is a RR of 1.55 which, as shown above, is only half of the level required to be deemed statistically valid. In addition, the study containing this statistic failed to compensate for skin type/subtype and, if they had done so, there would have been no increase in relative risk.
The bottom line is that the preponderance of scientific evidence proves that exposure to sunlight, UVR or a tanning device does not cause CMM and, regardless of what environmental factor causes the "mother" melanocyte cell to continue dividing and transform into a CMM, we believe that this factor can only be operational when an insufficient level of vitamin D exists. If our premise is correct, the potential prevention of CMM is yet another valid reason to maintain a sufficient level of vitamin D year-round. Therefore, if you want to enjoy good health and help prevent diseases like coronary heart disease, diabetes, MS, osteoporosis and cancer-possibly including CMM-you should maintain a blood level of vitamin D (25-OH-D) that is at least 120 nmol/L year-round. The best way to accomplish that objective is to take advantage of the controlled ultraviolet radiation exposure (CURE) found at a professional indoor-tanning salon.
After we wrote this article, we came across a study titled "Outdoor Work And Skin Cancer Incidence: A Registry-Based Study In Bavaria" by Radespiel-Troger, et al, published in the International Archives of Occupational Environmental Health. In it, researchers stated that the study confirms previous reports of the increased risk of basal cell carcinoma and squamous cell carcinoma in outdoor workers when compared to indoor workers, but that CMM risk was not significantly associated with outdoor work. Thus, it is irresponsible and unacceptable to claim that sunlight, UVR or a tanning device causes CMM when study after study (such as this one) show that there is no causal relationship between UVR exposure and the disease.
Patricia E. Reykdal owns and operates four tanning salons in Tucson, Ariz. Her husband, Donald L. Smith, is director of research of the Non-Ionizing Radiation Research Institute. Together, they have written more than 250 articles promoting sensible, moderate and controlled exposure to ultraviolet radiation