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Visual blog: Does latitude relate to colorectal cancer mortality?

Posted on: January 27, 2014   by  Jeff Nicklas

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In 2012, GLOBOCAN updated its worldwide atlas on cancer incidence, mortality and prevalence. GLOBOCAN is a project run by the International Agency for Research on Cancer (IARC), an affiliation of the World Health Organization. The 2012 atlas updates data from their atlas produced in 2008. The GLOBOCAN atlas includes data from 184 countries on all types of cancer. The atlas can be found here.

The GLOBOCAN atlas utilizes data collected by the IARC and then estimates incidence, mortality and prevalence for age and sex. For mortality, they used six different methods to gather the data. Then, the data for each country is gathered and mortality rates are listed as the total number, the crude rate, the age-standardized rate (ASR), and the cumulative risk.

Of importance is the ASR for mortality. This method standardizes the age of the population to essentially control for age and then looks at the rate of mortality per 100,000 people. This allows for the comparison of different populations that differ in age.

Overall the project indicates that in 2012 alone, there were an estimated 14 million cases of all cancers and 8.2 million deaths worldwide. Looking at specific cancers worldwide, they found that there were 1.6 million cases of breast cancer and 522,000 deaths. Their data also showed that in colorectal cancer, there were roughly 1.3 million cases and 694,000 deaths worldwide.

Colorectal cancer is the third most common cancer excluding all skin cancers. Colorectal cancer, which describes both colon and rectal cancer (colon cancer being the more common of the two), is a form of cancer that occurs in either the colon or the rectum. Colorectal cancer first develops as small abnormal growths, called polyps, inside the rectum or colon. If these are diagnosed early on, treatment can be highly successful.

While data hasn’t always been conclusive, researchers have been interested in the potential link between cancer and vitamin D for some time now. Studies have shown that vitamin D can effect cancerous cells through differentiation and apoptosis, and by inhibiting the proliferation and metastatic potential of cancerous cells.

Colorectal cancer was the first cancer to be suggested as having a link with vitamin D. Since then, research has shown that vitamin D appears to be related to overall prognosis in those with colorectal cancer. A prospective cohort study in 2008 found that those with colorectal cancer in the highest quartile of vitamin D levels had a 39% reduced likelihood of dying compared to those in the lowest quartile.

Ng, K. et al. Circulating 25-Hydroxyvitamin D levels and Survival in Patients with Colorectal Cancer. Journal of Clinical Oncology, 2008.

If past research suggests that vitamin D plays a role in colorectal cancer survival, could there be a relationship between latitude and colorectal cancer mortality?

Researchers first suggested a link between cancer survival and latitude back in 1941, when Dr. Frank Apperly thought there to be a direct benefit of sun exposure to cancer mortality.

Apperly, F. L. The Relation of Solar Radiation to Cancer Mortality in North America. Cancer Research, 1941.

Then in the 1980’s, it was hypothesized by Drs. Frank and Cedric Garland that sun exposure was directly linked to colorectal cancer mortality.

Google Visualization API Sample

As this map shows, the relationship isn’t perfect. Countries closer to the equator, such as Uruguay and Jordan show high rates of mortality. While Uruguay’s high mortality rates may be due to socioeconomic factors or lifestyle factors, such as high rates of smoking, Jordan may offer a different explanation.

Where Jordan is situated allows for almost year round vitamin D production from the sun. A possible explanation for the high mortality rates, then, could be that despite the relatively low latitude, cultural and religious practices – such as wearing heavy clothing – lead to low sun exposure, similar to countries at northern latitudes. This explanation has pitfalls, however, as neighboring countries have lower mortality rates.

Even with these kind of outliers, we can still see a relationship between latitude and colorectal cancer mortality. To get a better understanding, we can look at this data on a bar chart from the country closest to the equator to the country furthest from the equator, and we can still see the trend.

Colorectal Chart

In summary, this data appears to show a relationship between mortality and survival from colorectal cancer and latitudinal location. GLOBOCAN is an enormous project and is able to provide the public with an astonishingly large amount of data on not only colorectal cancer, but on all cancers for all ages and both sexes.

While there is okay data on latitude and colorectal cancer, further study is still needed to define link between sun exposure, vitamin D and colorectal cancer. See our colorectal cancer and vitamin D summary for more information.

Source

World Health Organization. GLOBOCAN 2012: Estimated Cancer Incidence, Mortality and Prevalence Worldwide in 2012. International Agency for Research on Cancer, 2012.

1 Response to Visual blog: Does latitude relate to colorectal cancer mortality?

  1. hlahore@gmail.com

    The scores of studies of Colorectal Cancer and vitamin D are overviewed at
    http://www.vitamindwiki.com/tiki-index.php?page_id=64
    In a nutshell: There is extremely strong evidence that > 40 ng of vitamin D protects against Colon Cancer
    There are, for example, 40 intervention trials of Coloncancer with Vitamin D intervention
    (It looks very promising)

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