The death rate from all causes of death for a population in a given time period.

An infectious disease caused by the novel coronavirus SARS-CoV-2. COVID-19, or coronavirus disease 2019, was first identified in Wuhan, China, in late 2019. The disease manifests primarily as a lower respiratory illness, but it can affect multiple organ systems, including the cardiovascular, neurological, gastrointestinal, and renal systems. Symptoms include fever, cough, fatigue, shortness of breath, and loss of smell and taste. Some infected persons, especially children, are asymptomatic. Severe complications of COVID-19 include pneumonia, sepsis, acute respiratory distress syndrome, kidney failure, multiple organ dysfunction syndrome, and cytokine storm. Treatments currently involve symptom management and supportive care. Mortality varies by country and region, but approximately 6 percent of people living in the United States who are diagnosed with COVID-19 expire.[1] 1

A type of white blood cell. Macrophages engulf and digest cellular debris, foreign substances, microbes, cancer cells, and oxidized LDL in a process called phagocytosis. After phagocytizing oxidized LDL, macrophages are referred to as foam cells.

A type of study that analyzes the data derived from multiple studies. Meta-analyses apply objective, statistical formulas to identify a common effect.

A type of white blood cell, also known as a granulocyte. Neutrophils are the most abundant form of blood cell, comprising approximately 60 percent of total cells. They ingest, kill, and digest microbial pathogens, and are the first cells recruited to acute sites of injury. Neutrophils can infiltrate brain structures, driving inflammation and increasing the risk for neurodegenerative disorders, such as Parkinson's disease and Alzheimer's disease.

In general, anything that can produce disease. Typically, the term is used to describe an infectious agent such as a virus, bacterium, prion, fungus, or other microorganism.

A study in which people are randomly allocated to receive one of several clinical interventions. One of these interventions is the standard of comparison or control. The control may be a standard practice, a placebo, or no intervention at all.

A fat-soluble vitamin. Vitamin A is a collective term that includes retinol, retinal, and retinyl esters. Vitamin A plays key roles in immune function, reproduction, and cellular communication. It is best known for its role in supporting eye health and the processes involved in vision. Vitamin A also supports cell growth and differentiation and participates in the normal formation and maintenance of the heart, lungs, kidneys, and other organs. Dietary sources of vitamin A include liver, fish oils, milk, eggs, leafy green vegetables, orange and yellow vegetables, tomato products, fruits, and some vegetable oils.