Final answer:
Heart disease and drug overdoses are leading causes of death for people under 40 in the United States, while acute respiratory infections, diarrheal diseases, and malaria are prominent among children under five in low-income countries.
Step-by-step explanation:
The number 1 killer of people under the age of 40 varies by region and country. In the United States, heart disease and accidental deaths from drug overdoses are leading causes of death for this age group. Heart disease can be attributed to lifestyle factors such as a sedentary lifestyle and high trans-fat diets. Drug overdoses, particularly from heroin and opioid painkillers, have seen a significant increase in recent years. Injuries, including head and traumatic brain injuries, often resulting from accidents such as falls or vehicle-related incidents, are also major contributors to mortality among the under-40 population.
Worldwide, other factors such as infections, malnutrition, and poor water and sanitation greatly affect child mortality, particularly in low-income countries. Diseases like pneumonia, diarrhea, malaria, and conditions arising from preterm births are often preventable or treatable, and the WHO emphasizes the importance of affordable interventions such as immunization and quality care by trained health providers.
When it comes to youth specifically, in low-income countries, the most frequent causes of death for children under five are acute respiratory infections, diarrheal diseases, and infectious diseases such as malaria, with contributing factors such as malnutrition playing a significant role.