Looking at the global distributions of breast and prostate cancer points us to consider its possible association with artificial light exposure at night (Figure 1&2).
Figure 1. Breast cancer rates (per 100,000). Source: (Haim & Portnov, 2013)
Figure 2. Prostate cancer rates (per 100,000). Source: (Haim & Portnov, 2013)
Not only do we detect an oddly similar global distribution of breast and prostate cancer, we also see that cancer incidence rates vary in accordance with artificial light exposure at night. In particular, besides cancer incidence rates being higher in developed countries vis-a-vis developing countries, they are also higher in extreme latitudes which often observe a high exposure to artificial lights to combat a lack of natural illumination. This provides further concretises the association between breast and prostate cancer with light pollution at night.
This association has been studied by Haim and Portnov (2013) who found that proxies for development levels of countries such as per capita GDP and electricity consumption explain breast and prostate cancer variations equally well. Furthermore, their studies revealed that national per capita electricity consumption explains variations in country-specific cancer rates not captured by per capita GDP.
Light and Cancer Risk
In spite of such evidence, it might be difficult to understand how a seemingly harmless light exposure can become a risk factor for certain cancers. Here’s how:
1. Melatonin Suppression
As discussed in former posts, artificial light can suppress the production of pineal melatonin hormone which occurs at night. What is significant to cancer, in this case, is that melatonin has tumour-inhibiting properties. Hence, disruptions to its production have the potential to alter the degree to which estrogen receptors combine and hence weaken our resistance to the development of breast and prostate cancer.
2. Disruption to Circadian Rhythms
The disruption to our circadian rhythm is a less well-researched explanation and an explanation of how light indirectly increases our cancer risk. As our circadian rhythms are disrupted by night light exposure, our immune system becomes stressed and hence becomes more susceptible to the development of various diseases, including breast and prostate cancer.
Why It Matters
If these associations were to be established as causation, its effects will be significant in terms of exposure magnitude. People exposed to high intensities of artificial light at night (or whenever melatonin production occurs) may be at high risk of breast and prostate cancer. This group includes people who work at night and may also extend to people who regularly studies, has an active nightlife, and even those who sleep with the light on.
For a condensed understanding of artificial light exposure at night on break cancer risk, the following video provides a brief summary of this association and briefly covers why the consumption of melatonin pills is not a viable solution as opposed to tackling the light source head-on.
Till next time!
References:
- Haim, A., & Portnov, B. A. (2013). Light pollution as a new risk factor for human breast and prostate cancers. Springer Science & Business Media. https://link-springer-com.libproxy1.nus.edu.sg/book/10.1007/978-94-007-6220-6