Why Do People Die?

The question seems straightforward: why do people die?  Answering it is surprisingly difficult.  One could take the biochemistry perspective and explore the molecular disturbances–such as DNA mutations–that cause individual cells to stop functioning.  Or, from the physiology perspective, one could describe the organ system perturbations–such as shock from blood loss–that cause a human being to cease having independent brain and/or heart activity.  Lastly, from a public health perspective, one could discuss the various causes of death as categorized by mechanism.  Each of these three perspectives offers a unique insight into what it means to be a human and what it means to die.  The public health vantage is the topic for today: what are the top causes of death around the world?  Let’s take a look.

If one considers broadly all ages, both sexes, and all countries around the world, the top five causes of death for the most recent year on record are the following (1):

TopMortality_world_2015

This list is short and simple and easy to understand, but digging into the details can prove illuminating.  Within the general category of “heart disease,” the largest player by far is ischemic heart disease–namely, heart attacks.  Among all cancers, the leading type is lung cancer, followed by liver cancer, colon cancer, and stomach cancer.  Stroke splits into two forms: hemorrhagic strokes, where a person bleeds into their brain, and ischemic strokes, where a clot abruptly cuts off blood flow to a portion of the brain.  Chronic respiratory disease consists primarily of chronic obstructive pulmonary disease, or COPD, a condition caused almost exclusively by smoking.  Unintentional injuries encompass many different mechanisms, but the most prevalent is motor vehicle crashes (1).  Note that none of the major global causes of death is infectious in nature; in public health terms, they are “noncommunicable” diseases, meaning they are not caused by infection with a microbial organism.  If one were to ask, then, in the most general sense possible, “What is the main reason people die around the world?,” the answer would be noncommunicable heart disease.

The data become more interesting when one begins to examine population subcategories.  For instance, comparing the poorest countries in the world versus the richest, the lists of top causes of death show some striking differences (1):

TopMortality_byincome

Among poorer populations, the noncommunicable diseases seen globally play a smaller role–though, notably, they still feature as prominent causes of death.  In the place of these chronic conditions, we see infectious diseases such as pneumonia and diarrhea.  For citizens of the USA or Western Europe, it’s hard to imagine someone dying of diarrhea; but the fact remains, it ranks as the fifth-leading cause of death in the world’s poorest regions.  In contrast, among the world’s wealthiest populations, as in the overall global list, infectious diseases do not appear anywhere in the top five causes of death, and heart disease and cancer remain the two biggest killers.  The category of neurological disease includes chronic degenerative disorders such as Alzheimer dementia and Parkinson disease, neither of which features prominently in poorer settings.  Thus, stratifying the global population by even a single metric, economic status, begins to reveal much wider variation in disease burden than one might have expected based on the overall world data.

Next, we narrow our focus even more, to a single country.  In the United States, the pattern of disease mortality for all ages and both sexes appears similar to that of wealthy countries in general (2, 3):

TopMortality_USA_2015

Note, though, a few differences.  Neurological disorders fall just outside of the top 5 for the US, with Alzheimer dementia ranking in sixth place (2).  Heart disease remains in first position in the US, whereas it has fallen second to cancer among wealthy countries worldwide.  Despite the US having abundant cardiologists, cardiac catheterization labs, and even entire hospitals devoted to nothing but heart problems, heart disease still kills more Americans than does any other cause.  There are many potential explanations for this observation–to be explored in later blog postings!  The US has managed to push stroke to last place in its top 5, while unintentional injuries–mostly car crashes–figure third in the US list, much higher than they do among wealthy countries at large.  These differences between the US and other wealthy countries highlight that even within groups sharing similar demographics there exists variation in the array of diseases faced.

As a former high school teacher, I believe young people represent the most important subgroup within any population.  They literally represent the future of that country, and their health statuses and skill sets will determine the capabilities of the country in twenty years’ time.  Unapologetically, then, I tend to focus my clinical and public health endeavors on youth.  On that note, we turn now to the mortality burden among US young people.  In the US in 2014, the top causes of death for various young age groups were the following (3):

TopMortality_USAyouth_2014

Immediately, one notices that the causes of death for young people differ from the causes of death for the country’s population as a whole.  Other than pediatric cancers and rare birth defects, the mechanisms that kill youth in America are not chronic conditions like heart disease but are largely preventable, often behavior-related, traumatic etiologies.  Car crashes, suicides, homicides.  These are the things killing our kids; and we can adopt measures to prevent or at least to mitigate these traumatic forms of death.  We can engineer safer cars, pass automotive laws that ban texting-and-driving, design smart guns that prevent unauthorized access, improve inner-city cohesion to counteract gang violence, etc.  The young people in a population warrant special public health attention, not only because of their relative value to society but also because of the unique set of life-threats that afflict them.

One final, related note on youth.  We’ve explored the causes of death for young people in the US, but another question one could ask is: what is the actual risk of death?  For children, ages 5-9, the risk of death is almost zero!  Out of every 100000 kids in America aged 5-9 years, only 11.5 die every year–giving a risk of 0.012%.  This is truly incredible when one steps back and appreciates the significance; we as a society have virtually eliminated the risk of death for an entire portion of the population.  Pretty cool.  Unfortunately, the risk of death starts to climb once a child ages into the preteen and adolescent years (3).  As already noted, youth in these age ranges tend to die not from medical illness but from trauma, much of which is likely related to increased risk-taking behaviors.  This observation is tragic, but also encouraging because it means we can potentially affect the statistics.  If as mentioned earlier we apply engineering, policy, and/or socioeconomic interventions to reduce the mortality impacts of adolescents’ risk-taking tendencies, then perhaps we can lower the teen death rate towards that of younger children–thereby saving thousands of lives for future America.

As we’ve seen, the answer to “why do people die” can vary considerably depending on which population one examines.  Further, the preceding discussion has focused only on causes of death; but short of death, diseases can also cause tremendous harm through injury, which is a topic for future discussion.  For now, we’ve established the primary causes of death around the world and at home in the US, and we can now begin to look at those individual etiologies and at ways to combat them.

References

  1. Global Health Estimates 2015: Deaths by Cause, Age, Sex, by Country and by Region, 2000-2015. Geneva, World Health Organization; 2016.
  2. Xu JQ, et al. Mortality in the United States, 2015. NCHS data brief, no 267. Hyattsville, MD: National Center for Health Statistics. 2016.
  3. Heron M. Deaths: Leading causes for 2014. National Vital Statistics Reports; Vol 65 (5). Hyattsville, MD: National Center for Health Statistics. 2016.

Author: Thoughts, MD

Itinerant doctor | Intermittent blogger | Dilettante Photographer

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