Vitamin D Council Glossary

Haplotype

A set of alleles of a group of closely linked genes which are usually inherited as a unit.

Heliotherapy

Method of treating illness by exposure to ultraviolet radiation (sunlight).

Hemoglobin

Protein molecule in red blood cells that carries oxygen from the lungs to bodily tissues and carbon dioxide from tissues to the lungs.

High Performance Liquid Chromatography (HPLC)

Important analytical tool for separating and quantifying components in complex liquid mixtures.

High-density lipoprotein (HDL)

The smallest of the lipoproteins and also the densest due to a high proportion of protein. High concentrations of high-density lipoproteins (HDL), such as those over 60 mg/dL, are said to help protect against cardiovascular disease.

Hippocampus (Hippocampal)

A major component of the brains of humans and other mammals.

Homeostasis

Resistance to change. How the body maintains its internal equilibrium to insure proper functioning.

Homocysteine

An amino acid in the blood. High blood levels of homocysteine increase risk of coronary heart disease, stroke, and peripheral vascular disease.

Homozygous

Having identical alleles for a single trait.

Hormone

Chemical messenger from one cell, or group of cells, to another.

Humoral immune response

Aspect of immunity that is mediated by secreted antibodies produced in the cells of B-lymphocytes.

Hydrolysis

Breakdown of organic materials due to reaction with water.

Hydroxylapatite (hydroxyapatite,HA)

Naturally-occurring mineral form of calcium apatite.

Hypercalcemia (Hypercalcaemia)

An elevated calcium level in the blood that is often indicative of other diseases, especially hyperparathyroidism and malignancy. Hypercalcemia can also occur due to an excessively high intake of vitamin D.

Hypervitaminosis A

Occurs when the maximum limit for liver stores of retinoids is exceeded, resulting in the excess vitamin A entering circulation and causing systemic toxicity. Most cases of vitamin A toxicity result from an excess intake of supplemental vitamin A in the form of retinol.

Hypervitaminosis D

Excessively high blood calcidiol level.

Hypoalbuminemia

Medical condition where serum levels of albumin are abnormally low.

Hypocalcemia (Hypocalcaemia,Hypocalcaemic)

A type of electrolyte disturbance in which there are low blood levels of calcium.

Hypothalamus

Region at the base of the third ventricle in the brain that controls an immense number of bodily functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland.

Hypotonic

Having deficient tone or tension, as in a hypotonic muscle.

Hypovitaminosis D (Vitamin D deficiency)

Medical condition where a lack of vitamin D puts one at risk for diseases associated with vitamin D deficiency.