Glossary of Terms & Definitions
Listed Alphabetically - "D"

Decarboxylation: A chemical reaction involving the removal of a carboxyl (-COOH) group from a compound.

Decussation: A crossing-over; usually refers to the crossing of 90% of the fibers in the large motor tracts to opposite sides in the medullary pyramids.

Deep fascia: A sheet of connective tissue wrapped around a muscle to hold it in place.

Delta cell: a cell in the pancreatic islets (islets of Langerhans) in the pancreas that secretes somatostatin.  Also called a D cell.

Dementia: Significant loss of intellectual abilities such as memory capacity, severe enough to interfere with social or occupational functioning. Criteria for the diagnosis of dementia include impairment of attention, orientation, memory, judgment, language, motor and spatial skills. By definition, dementia is not due to major depression or psychosis. Alzheimer's disease is the most common cause of dementia. Other causes include but are not limited to: AIDS, alcoholism (the dementia is due to thiamine deficiency), insufficient blood flow to the brain (vascular dementia), brain injury, brain tumors, drug toxicity, multiple sclerosis, and infections of the central nervous system.

Dental caries: cavities or holes in the outer two layers of a tooth--the enamel and the dentin. Dental caries are caused by bacteria which metabolize carbohydrates (sugars) to form organic acids which dissolve tooth enamel. If allowed to progress, dental caries may result in tooth decay, infection, and loss of teeth.

Depletion-repletion study: a nutritional study designed to determine the requirement for a specific nutrient. Generally, subjects are placed on a diet designed to deplete them of a specific nutrient over time. Once depletion is achieved, gradually increasing amounts of the nutrient under study are added to the diet until the individual shows evidence of sufficiency or repletion.

Dermatitis: inflammation of the skin. This term is often used to describe a skin rash.

DEXA: dual energy X-ray absorptiometry. A precise instrument that uses the energy from very small doses of X-rays to determine bone mineral density (BMD) and to diagnose and follow the treatment of osteoporosis.

DEXTRIN: Dextrin is any one of a number of carbohydrates having the same general formula as starch but a smaller and less complex molecule. They are polysaccharides and are produced as intermediate products in the hydrolysis of starch by heat, by acids, and by enzymes. Their nature and their chemical behavior depend to a great extent on the kind of starch from which they are derived. For commerical use dextrin is prepared by heating dry starch or starch treated with acids to produce a colorless or yellowish, tasteless, odorless powder which, when mixed with water, forms a strongly adhesive paste. It is used widely in adhesives, e.g., for postage stamps, envelopes, and wallpapers, and for sizing paper and textiles.

DHA: (Docosahexaenoic Acid – Omega-3 fatty acid) (Pronunciation: doh-KOH-sah-HEX-ah-een-OH-ic). DHA (docosahexaenoic acid is and omega-2 fatty acid that belongs to the class of nutrients called essential fatty acids. DHA, abundant in cold-water fish, is essential for neurological development and for normal brain function in adults. It lowers serum triglyceride levels, making it useful for preventing cardiovascular and other problems. DHA deficiencies are associated with difficulties in learning, attention deficit hyperactivity disorder, unipolar depression, aggressive hostility, senility, sporadic Alzheimer’s, cystic fibrosis and other problems. DHA supplementation improves learning and is useful for hypertension, arthritis, atherosclerosis, depression, adult-onset diabetes, blood clots and some cancers. Read More...

Diabetes (diabetes mellitus): a chronic condition associated with abnormally high levels of glucose (sugar) in the blood. The two types of diabetes are referred to as insulin-dependent (type I) and non-insulin dependent (type II). Type I diabetes results from a lack of adequate insulin secretion by the pancreas.  Type II diabetes (also known as adult-onset diabetes) is characterized by an insensitivity of the tissues of the body to insulin secreted by the pancreas (insulin resistance).

Diabetic ketoacidosis: a potentially life-threatening condition characterized by ketosis (elevated levels of ketone bodies in the blood) and acidosis (increased acidity of the blood). Ketoacidosis occurs when diabetes is not adequately controlled.

Diastolic blood pressure: the lowest arterial blood pressure during the heart beat cycle. The diastolic blood pressure is measured while the heart muscle is filling with blood.

Differentiation: changes in a cell resulting in its specialization for specific functions, such as those of a nerve cell. In general, differentiation of cells leads to a decrease in proliferation.

Diffusion: a process, which does not require energy expenditure, by which particles in solution move from a region of higher concentration to one of lower concentration.

Dimer: a complex of two protein molecules.  Heterodimers are complexes of two different proteins, while homodimers are complexes of two of the same protein.

Diuretic: an agent that increases the formation of urine by the kidneys, resulting in water loss from the individual using the diuretic. 

DNA: deoxyribonucleic acid.  A long thread-like molecule made up of large numbers of nucleotides. Nucleotides in DNA are composed of a nitrogen containing base, a 5-carbon sugar (deoxyribose), and phosphate groups. The sequence of bases in DNA serves as the carrier of genetic (hereditary) information.

Docosahexaenoic Acid: See DHA

Double blind: refers to a study in which neither the investigators administering the treatment nor the participants know which participants are receiving the experimental treatment and which are receiving the placebo.

DRI: dietary reference intake. Refers to a set of at least four nutrient-based reference values (RDA, AI, UL, EAR), each with a specific use in defining recommended dietary intake levels for individual nutrients in the U.S. The DRIs are determined by expert panels appointed by the Food and Nutrition Board of the Institute of Medicine.

DV: daily value. Refers to the dietary reference values required as the basis for declaring nutrient content on all products regulated by the U.S. Food and Drug Administration (FDA), including nutritional supplements. The DVs for vitamins and minerals reflect the National Academy of Sciences' 1968 RDAs, and do not reflect the most up to date Dietary Reference Intakes.