Why the Human Development Index is Correlated with the Incidence of Colorectal Cancer?
Colorectal cancer (CRC) has become the third commonest diagnosed cancer and the second leading cause of cancer death in the world. There were about 1.85 million new CRC cases and 0.88 million CRC-related deaths in 2018, in comparison with 1.4m new cases and 0.7m deaths in 2012. (Wong et al., 2019 and Arnold et al., 2016)
One of the established causes of CRC is the consumption of processed meat that we have discussed before (Yiu, 2019). However, besides processed meat, there may be some other causes, as Arnold et al. (2016) has recently studied the global (184 countries) trend of the incidence rate and the mortality rate of colorectal cancer, and found a positive correlation between the UN Human Development Index and the incidence rate of colorectal cancer, as shown in Figure 1.
Human Development Index (HDI) is developed by the United Nation and is the geometric mean of normalized indices for each of the three dimensions, viz. (1) Health Dimension measured by life expectancy at birth, (2) Education Dimension measured by years of schooling, and (3) Standard of Living Dimension measured by gross national income per capita. (UNDP, 2018)
Since it is quite unlikely that the age-standardized incidence rate of colorectal cancer is related to higher life expectancy at birth or years of schooling, the correlations between the two are commonly regarded as the consequence of consuming more westernized food when the people can afford to, including more processed meat.
Although the study did not include Hong Kong, I found the data of Hong Kong matched the correlation well. According to UNDP (2018), the Human Development Indicator Hong Kong in 2012 was 0.911 (0.933 in 2018). According to CHP (2019), the age-standardized incidence rate and mortality rate of colorectal cancer (both sexes) in 2012 were about 38 (per 100,000 standard population) and 14 (per 100,000 standard population), as shown in Figures 2 and 3.
The red dots on Figure 4 show the correlations of the two in Hong Kong 2012 (aligned with all other data points). Their correlations fall in line with the global situations. It is also noted that the positive correlation of HDI and the incidence rate is much stronger than that with the mortality rate. The reason for a lower correlation between HDI and the mortality rate is probably due to the effectiveness of the medical care of high HDI countries.
Arnold et al (2016) divide the trends into 3 groups: Group A is of countries with both the rates of incidence and mortality of colorectal cancer are increasing; Group C is of countries with both the rates are decreasing; and Group B is of countries with the rate of incidence increasing, but the rate of mortality decreasing.
Hong Kong belongs to Group B as shown in Figures 2 and 3 above. Figure 5 shows another 2 examples of group B countries. The situations are highly similar to that in Hong Kong.
Group C is the most intriguing group as their HDIs are relative high, but they can achieve both declining rates of incidence and mortality of colorectal cancer. They basically refute the hypothesis that colorectal cancer is the byproduct of a higher living standard. At least, they prove that the rates can be cut.
There are 9 countries in Group C, viz. Australia, Austria, Czech Republic, France, Iceland, Israel, Japan, New Zealand, USA. Among them, only Japan is located in Asia and its trend, I suppose, is more insightful. Figure 6 shows the trends of the rates of incidence and mortality of Japan and New Zealand (omitting the other 7 countries’ without loss of the generalities). Comparing the peaks of the curves of the two countries, the peaks of Japan are relatively lower (the peaks of the incidence rate and mortality rate for male patients are at about 40 and 18, in comparison with 50 and 27 in New Zealand, respectively. It should be more difficult for countries with lower peaks to reduce the rates, according to the 80–20 rule. How can Japan achieve a reduction in the two rates of colorectal cancer, especially the rate of incidence, justifies further investigation.
I cannot find any particular relevant studies on Japan though, there have been some pooled studies on the association between dietary factors and colorectal cancer. For example, Hou et al. (2013) reviewed the relevant literature and referred to a prominent theme of studies involves metabolic and insulin-related pathways. Among them, a recent study (Meyerhard et al., 2007) closely examined the Western diet and the role of dietary glycemic measures on colorectal cancer, and it found that high carbohydrate intake and glycemic load significantly increased both incidence and mortality.
The findings of this theme of studies probably help explain the correlation between HDI and the incidence of colorectal cancer. High insulin-spiking carbohydrate intake and high glycemic load are the two hallmarks of food intake in most of the high GDP countries. Japan is one of the few exceptions. Since most of these foods are addictive and readily available in fast-food restaurants, cafes, convenient stores and supermarkets, people would consume more involuntarily when they can afford to.
The recent trends of Whole-Food-Plant-Based diet, Veganism, and Low-Carb-Healthy-Fat diet, especially in the US, may be one of the reasons that can explain the downward trend in the rate of incidence of colorectal cancer in some high HDI countries.
Arnold, M., Sierra, M.S., Laversanne, M., Soerjomataram, I., Jemal, A. and Bray, F. (2016) Global patterns and trends in colorectal cancer incidence and mortality, Gut, Jan. 27. 1–9. doi:10.1136/gutjnl-2015–310912
CHP (2019) Colorectal Cancer, Health Topics, Centre for Health Protection, Department of Health, HKSAR Government, Apr. 8. https://www.chp.gov.hk/en/healthtopics/content/25/51.html
Hou, N., Hui, D. and Dignam, J.J. (2013) Prevention of colorectal cancer and dietary management, Chin Clin Oncol., Jun; 2(2): 13. doi: 10.3978/j.issn.2304–3865.2013.04.03
Meyerhardt JA, Niedzwiecki D, Hollis D, et al. (2007) Association of dietary patterns with cancer recurrence and survival in patients with stage III colon cancer. JAMA., 298:754–64.
UNDP (2018) Human Development Reports, United Nations Development Programme, http://hdr.undp.org/en/content/human-development-index-hdi
Wong, M.C.S., Ding, H., Wang, J., Chan, P.S.F. and Huang, J. (2019) Prevalence and risk factors of colorectal cancer in Asia, Intestinal Research, 17(3), 317–329. https://irjournal.org/upload/pdf/ir-2019-00021.pdf
Yiu, C.Y. (2019) Processed Meat Consumption and CHD, diabetes and colorectal cancer, Medium, Jul. 27. https://medium.com/@edwardyiu/processed-meat-consumption-and-chd-diabetes-and-colorectal-cancer-270593f8c8b3