What are the top 10 deadliest diseases and what is causing them?

top 10 deadliest diseases

Last Updated December 20th, 2021

 A sneak peek into global mortality

What is the biggest threat to human lives? What is the one thing human beings should be scared of the most? A quick scroll through your daily news feed (or a scan of the newspaper headlines, for the old schoolers) will tell you that you should be scared of bombings or natural disasters or even the war.

However, a close look at the facts pertaining to global mortality paints a completely different picture. It’s not the danger of unforeseen natural disasters or the mass slaughter of human lives by terrorist groups that rank number one in the list of reasons for human mortality.

Counting the 56.9 million deaths that occurred in 2016, a whopping 54% of these were not caused by floods, fires, or bombings. These were caused by long-term chronic ailments that progress gradually and end up claiming the lives of millions each yearYes.

For a substantial period for more than a decade (15 years to be precise), these common yet deadly diseases have consistently featured as the biggest killers of human lives. The only non-disease entity featuring in the top 10 killers of human beings is road accident and injury.

Ischemic heart disease, cerebral stroke, cancers, infections – these are the real killers of our generation. These widespread diseases have permeated every demography – ethnicity, gender, and age; and have become so commonplace that instead of viewing them as threats we have started accepting these as a part of our lifestyle. Let us take a step back and see what trends one can observe in global mortalities.

Global mortalities: Some shocking discoveries

Shift from infections to cardiac diseases

In 1997, out of the 52.2 million deaths that were recorded worldwide, infections and parasitic diseases were the number 1 cause of death amounting to a total of 17.3 million deaths. The second leading cause in this list was circulatory diseases.

Shift from to cardiac diseases

With substantial advances in vaccinations and improvement in sanitation levels, infectious disease mortalities have thankfully decreased. However, now cardiovascular diseases have become the number reason for deaths. As per the most recent statistics, heart diseases are responsible for 17.7 million deaths every year.

While infections still dominate the mortality scene in low and middle-income countries, it has been observed that as economies grow, non-infectious diseases gradually become leading causes of deaths. This can be largely attributed to typical western dietary and lifestyle habits such as smoking, high-cholesterol foods, stress, obesity, and sedentary lifestyle.

Adult mortality rate (high vs. low-income countries)

Adult mortality rate is defined as the probability that a person (over the age of 15 years) will succumb to death before reaching the age of 60. As per the statistics released by the WHO, the global adult mortality rate is 142 per 1000. However, this figure is highly variable from region to region.

For example, in many African nations, this number is as high as 360 per 1000 (Chad), 352 out of 1000 (Nigeria), and even as high as 483 out of 1000 (Lesotho)! If we look at the developed countries, this figure falls drastically. For Canada it is 63 out of 1000, Spain is 56 out of 1000, and the USA it is 114 out of 1000.

Adult mortality rates

Overall the trend that can be observed is that adult mortality is highest in low-income countries whereas the opposite is true for high-income countries.

 Child and neonatal deaths

Looking at the trends of child deaths (under 5 years) all over the world, as per the latest reports, 50% of all child deaths are caused by 4 communicable (but highly preventable) diseases. These diseases are pneumonia (920,000 deaths), diarrhea (526,000 deaths), malaria (306,000 deaths), and meningitis (116,000 deaths).

child & neonatal deaths

When you look at the neonatal mortality rates (neonatal – first 28 days after birth), the global neonatal mortality rate is 18 per 1000. Globally, 2.5 million neonatal deaths occur every year. This translates to 7,000 neonatal deaths per day!

 Lethal risk factors

The five risk factors that are responsible for a majority of deaths worldwide are – high blood pressure, tobacco consumption, high blood sugar, physical inactivity, and obesity.   The next two factors in this list are unsafe sex (sexually transmitted diseases) and alcohol use. The top 5 risk factors account for a whopping 37.6% of all deaths that translates to 22 million deaths across the globe every year (high-income countries)

Lethal risk factors

The above factors are a representation of adult deaths of course.  The major risk factors associated with child deaths are malnutrition, underweight, contaminated water, air pollution, and climate change.

And for the young adults, the majority of health burden and mortalities are associated with risk factors such as substance abuse & addiction, unsafe sex & lack of contraception, nutritional deficiencies (iron), and child sex abuse.

 Diet patterns and global mortalities

Did you know that obesity and overweight cause more deaths than undernutrition? Today, 65% of the world’s population resides in countries where obesity and overweight claim more human lives than malnutrition. This includes all developed countries and the major proportion of middle-income nations.

The most common and lethal dietary (and lifestyle) patterns that can be held responsible for a substantial number of diseases (and deaths) are – hypertension, high blood sugar, physical inactivity, obesity & overweight, high cholesterol, and low intake of fruits and vegetables.

Diet patterns global mortalities

In high-income countries, these represent a quarter of all mortalities whereas in low and middle-income countries this figure is slightly less, around 18%. The point to be noted here is that even in low and middle-income countries these factors are still a significant entity of overall mortality.

Now that we have a much clearer idea of what diseases are killing millions around the world, what trends are observed in adult and child deaths, and what behaviors/risk factors translate to the most number of deaths, let us take a detailed look into the world’s deadliest diseases (by numbers).

#1.  Cardiovascular Diseases

Global deaths per year = 17.7 million

Heart diseases, or rather ischemic heart diseases, are the biggest killers of human beings. Ischemic refers to the restriction of blood supply in the arteries. Due to the short supply of blood, there is an inevitable shortage of oxygen that halts cellular functions. One of the most drastic consequences of ischemia is a sudden cardiac arrest. It is usually a result of atherosclerosis – the formation of plaques within arteries that blocks normal circulation.

Arterial plaque is composed of fats, cholesterol, calcium, cellular wastes, and fibrin. A diet that heavy in saturated fats (animal fats), trans fat, and cholesterol is the primary reason for massive plaque build-up. In addition to these, high blood pressure results in rapid plaque deposition while tobacco smoke (mainly consisting of nicotine and carbon monoxide) causes weakening of the endothelium. Endothelium layer refers to the inner lining of the arteries.

Damaged endothelium sets up the perfect stage for plaque build-up. Similarly, physically inactive people tend to gain excessive body fats which, as we observed, can easily result in clogged arteries. The biggest take away from this information is that the biggest killer of human beings globally is a disease that can be largely prevented by following healthy living habits!

#2.  Cancer

Global deaths per year = 9.6 million

One of the most dreaded diseases in the world, cancer is second in the list of deadliest diseases. This is characterized by the accelerated growth of tumor cells.  Cancer begins in the form of a pre-cancerous lesion that rapidly progresses to become a malignant tumor. It can develop anywhere in the body and there are more than 100 different types of cancers diagnosed in humans.

There are three categories of agents that can cause cancer (carcinogens).  Physical carcinogens are those agents whose physical properties are responsible for the onset of malignancy. These include ionizing radiations, particulate matter, and even fibers such as asbestos. Chemical carcinogens are the ones whose toxic chemical composition triggers the process of carcinogenesis.  Tobacco smoke, pesticides, arsenic etc come under this category. Disease-causing pathogens (bacteria, virus, and parasites) interfere with normal cellular function by interacting with host cell DNA, thus causing metastasis or rapid spread of cancer.

The biggest risk factors at play here are infectious diseases, toxic exposure to carcinogens, and an unhealthy diet.  According to WHO, 30-50% of cancer cases can be prevented by carefully avoiding exposure to carcinogens and improving lifestyle habits.

#3.  Stroke

Global deaths per year = 6.2 million

Killing more than 6 million people across the globe every year, cerebrovascular stroke is the next big name in the global mortality list. A stroke occurs when the blood supply to the brain is cut off (by either a blood clot or bursting of a blood vessel) because of which brain cells immediately begin to die. Brain cells are incapable of regeneration, hence once a stroke occurs the brain damage it causes tends to have permanent debilitating effects.

80% of strokes are caused due to blood clots and these usually don’t present painful symptoms in the patient. The rest 20% are caused to internal bleeding within the brain which produces excruciating pain. It is estimated that every minute, stroke claims 6 lives. That translates to 1 death every 10 seconds.

As per recent statistics, 70% of all cases of stroke and 87% of all stroke-related deaths are reported to occur in low and middle-income countries. Technically speaking, the risk factors associated with ischemia (restricted blood flow) are the ones which are responsible for the onset of stroke or “brain attack”.

The very factors such as obesity, smoking, high blood pressure, diabetes, lack of physical activity that formed the basis of heart diseases (the #1 killer) are also the ones responsible for stroke (#3 in the deadliest disease list)

#4.  Chronic Obstructive Pulmonary Disease or COPD

Global deaths per year = 3.17 million

Next in the list of most deadly diseases is something that can be considered as a drastic aftermath of both unhealthy lifestyle choices and soaring levels of pollution – COPD. It stands for Chronic Obstructive Pulmonary Disease and as the name suggests, it is a chronic condition characterized by a severe obstruction in the lungs (pulmonary).

Chronic bronchitis and emphysema- these are the two pulmonary conditions that are categorized under COPD. Bronchitis occurs due to inflammation of bronchial tubes whereas emphysema occurs when the air sacs (alveoli) get damaged.  Both these conditions develop gradually and progressively.

The damage caused by COPD is permanent and this remains as an incurable disease. As you might have guessed, COPD is yet another consequence of tobacco smoking. Both active and second-hand smoking is directly responsible for it.

Increased exposure to air pollution (indoor and outdoor) is similarly responsible for the rising number of COPD cases and mortality. An important trend in COPD- related deaths is that almost 90% of all such fatalities occur in low and middle-income countries. A stark danger posed by COPD is that fetal exposure to environmental pollutants can heighten the risk of contracting this disease later in life.

Tobacco use and environmental pollution – both these largely controllable risk factors are at the grassroots of the number 4 killer disease.

#5.  Lower Respiratory Tract Infections

Global deaths per year = 2.74 million

The fifth leading cause of global deaths overall and the leading cause of deaths by infections is the category of LRTIs or Lower Respiratory Tract Infections.

This umbrella term encompasses the vapid presence of viral and bacterial agents in the lower respiratory tract, i.e, the alveolar sacs. Though mostly these are synonymous to pneumonia, other pulmonary conditions such as acute bronchitis and lung abscess can also be counted in this category.

Streptococcus pneumoniae (pneumococcal pneumonia), Haemophilus influenza type b (Hib), influenza and respiratory syncytial virus (RSV) – these are the most virulent agents responsible for LRTIs. Nearly 55% of all deaths due to LTRIs are caused by pneumonia. This infection is highly prevalent among children below 5 years of age. In fact, pneumonia is the number cause of child deaths in the world.

Pneumonia’s pervasive prevalence can be attributed to a handful of factors including childhood undernutrition and rampant air pollution (both indoor and outdoor). Another significant reason behind the catastrophic number of deaths caused by pneumonia is the emergence of drug-resistant bacteria (MRSA – Methicillin-Resistant Staphylococcus Aureus).

Overcrowding of hospital and residential places, lack of hygiene, and compromised immunity – these are also significant contributors to the widespread and lethal occurrence of LRTIs, especially pneumonia.

Top 10 deadly diseases

#6.  Diabetes Mellitus

Global deaths per year = 1.6 million

Though pancreas is a relatively small gland (6 inches long), its malfunctioning can culminate a profoundly widespread disease – diabetes.

It is a consequence of either reduced insulin production (type 1) or increased resistance to insulin (type 2).  There are more than 420 million diabetics worldwide. A sudden increase in obesity and overweight rates across the globe in the past 3 decades is posited to be the number 1 reason for the surge of diabetes.

According to WHO, the number of deaths caused by diabetes is projected to double between 2005 and 2030! Also, 4 out of every 5 deaths caused as a result of diabetes occur in low and middle-income countries.

High blood sugar level is a complex and potentially lethal condition as it can cause irreversible damage to vital organs including the kidneys, heart, and eyes. It also has a debilitating effect on the nerves and the blood vessels. Diabetes is also one of the leading factors to cardiac diseases (the #1 killer), kidney failures, and limb amputations.

Studies reveal that with 30 minutes of moderate exercise and a healthy diet can avert a majority of diabetes cases. Diabetes, just like cardiac illness or stroke, is a largely preventable cause of death.

#7.  Alzheimer’s disease and other dementias

Global deaths per year = 1.5 million

While most people associated Alzheimer’s and other dementia conditions with nothing more than memory loss and an inevitable part of aging, these conditions are in reality more than just that.

Dementia is an umbrella term that refers to a group of neurodegenerative conditions.  In simple terms, diseases where the functionality of the brain gradually reduces. And these are not related to memory alone.

Cognitive dysfunction due to dementia is an all-pervasive phenomenon.

It is marked by deterioration of memory, thinking, calculation, emotional, comprehension, judgemental, and linguistic capacity. The economic costs associated with this disease are staggering. The economic burden of dementia is close to $ 818 billion (as per 2016 reports) and is expected to become a trillion dollar disease by the end of 2018!

It’s not only the surging economic burden of dementia that is a cause of concern.

The alarming rate at which this disease is now being reported all over the world is dangerously shocking. Currently, there are roughly 46.8 million people with dementia worldwide (2015). Studies reveal that this figure is set to double every 20 years. This translates to almost 75 million patients is 2030 and 131.5 million in 2050. Every year roughly 10 million new cases are reported worldwide!

Every 3 seconds 1 person is diagnosed with dementia. 60-80% of all cases of dementia come under the category of Alzheimer’s.

And the most staggering fact about this condition is that this is the only disease featuring the list of top 10 deadliest diseases that can neither be completely prevented, cured or slowed down!

#8. Diarrheal diseases – Diarrhea and Food Poisoning

Global deaths per year = 1.4 million

Ranking 8th in the list of deadliest diseases are diarrheal diseases. These are the second leading form of infections associated with global mortality and the 2nd most common cause of death among children below 5 years of age.

Every day 2,195 children succumb to diarrheal diseases across the world. Children with HIV infection have 11 times higher mortality rate due to diarrhea than children without HIV infection.

The cause of death due to diarrhea is the severe loss of bodily fluids and electrolytes due to dehydration. Almost 88% of all cases of the diarrheal diseases can be attributed to contaminated water and lack of sanitation facilities.

The main cause of diarrheal infections is the rotavirus; it is responsible for acute diarrhea and also for roughly 40% hospitalizations in children under the age of 5.

Worldwide 2.5 billion people lack basic sanitation. The best ways to prevent these deathly infections are proper immunization against rotavirus and access to clean drinking water and basic hygiene.

#9. Tuberculosis

Global deaths per year = 1.34 million

25% of the global population is infected with the TB bacteria, however, not all of them develop symptoms of the disease.

This is the leading cause of death among HIV infected patients.  Even though the global incidence of tuberculosis is decreasing by 2% annually, the number of deaths it causes each year globally is alarmingly high.

A Multidrug-resistant bacterium that causes TB is found in roughly 558,000 cases every year. This type of TB bacteria has grown resistant to the most effective drug developed for treating TB, rifampicin. Early diagnosis and treatment TB saved more than 54 million lives between the years 2000 and 2017.

HIV infected people are 20-30 times more likely to develop the infection. 95% of all deaths caused due to TB occur in low and middle-income countries. South East Asian, Western Pacific, and African nations remain the worst TB hit areas.

 #10. Liver Cirrhosis

Global deaths per year = 1.2 million

The 10th leading cause of deaths worldwide is the chronic cirrhosis of the liver that kills around 31,000 Americans every year.

A huge proportion of the deaths can be averted by controlling chronic alcohol consumption. Hepatitis B and C infections are also responsible for causing liver tissue scarring that leads to cirrhosis.

The number of males succumbing to liver cirrhosis is twice that of females. 1 out of every 10 patients of liver cirrhosis doesn’t show any marked visible symptoms until more advanced stages of the disease. High cholesterol levels that result in fatty liver disease are also responsible for liver cirrhosis.

The most common symptoms of liver cirrhosis include jaundice, sudden weight loss, reduced appetite, and frequent bruising. The scarring of liver tissues in liver cirrhosis cannot be reversed.


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