A waxy lipid produced primarily in the liver and intestines. Cholesterol can be synthesized endogenously and is present in all the body's cells, where it participates in many physiological functions, including fat metabolism, hormone production, vitamin D synthesis, and cell membrane integrity. Dietary sources of cholesterol include egg yolks, meat, and cheese.

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

An essential mineral present in many foods. Iron participates in many physiological functions and is a critical component of hemoglobin. Iron deficiency can cause anemia, fatigue, shortness of breath, and heart arrhythmias.

The thousands of biochemical processes that run all of the various cellular processes that produce energy. Since energy generation is so fundamental to all other processes, in some cases the word metabolism may refer more broadly to the sum of all chemical reactions in the cell.

A chemical that causes Parkinson's disease-like symptoms. MPTP undergoes enzymatic modification in the brain to form MPP+, a neurotoxic compound that interrupts the electron transport system of dopaminergic neurons. MPTP is chemically related to rotenone and paraquat, pesticides that can produce parkinsonian features in animals.

The virus that causes severe acute respiratory syndrome, or SARS. First identified in China in 2002, SARS-CoV-2 is a type of coronavirus. It was responsible for an epidemic that killed nearly 800 people worldwide.

The virus that causes COVID-19. SARS-CoV-2 is one of seven coronaviruses known to infect humans. Others include SARS-CoV-1 (which causes severe acute respiratory syndrome, or SARS) and MERS-CoV (which causes Middle East respiratory syndrome, or MERS). SARS-CoV2 exploits the angiotensin-converting enzyme 2, or ACE2, receptor to gain entry into cells. The ACE2 receptor is widely distributed among the body's tissues but is particularly abundant in lung alveolar epithelial cells and small intestine enterocytes. SARS-CoV-2 binds to a cell's ACE2 receptor and injects its genetic material (RNA) into the cytosol. Once inside, the viral RNA molecules are translated to produce RNA-dependent RNA polymerase, also known as replicase, the enzyme critical for the reproduction of RNA viruses. The viral RNA is then packaged into infective virion particles and released from the cell to infect neighboring cells.

The highest level of intake of a given nutrient likely to pose no adverse health effects for nearly all healthy people. As intake increases above the upper intake level, the risk of adverse effects increases.

A fat-soluble vitamin stored in the liver and fatty tissues. Vitamin D plays key roles in several physiological processes, such as the regulation of blood pressure, calcium homeostasis, immune function, and the regulation of cell growth. In the skin, vitamin D decreases proliferation and enhances differentiation. Vitamin D synthesis begins when 7-dehydrocholesterol, which is found primarily in the skin’s epidermal layer, reacts to ultraviolet light and converts to vitamin D. Subsequent processes convert D to calcitriol, the active form of the vitamin. Vitamin D can be obtained from dietary sources, too, such as salmon, mushrooms, and many fortified foods.