Iodine uses follow from the properties of the element iodine.
Iodine is an element in Group 7 of the Periodic Table. Members Group 7 are also known as Halogens. Each iodine atom consists of 53 protons, 53 electrons plus some neutrons the quantity of which depends on the isotope of iodine (based on a mass number of 127 there would be 74 neutrons in each atom of iodine).
Iodine uses can be described in several categories.
As the element iodine plays important roles within the human body and human health, lists of iodine uses often start with biological uses of iodine within the human body. This leads easily onto uses of iodine in health-related contexts, such as its use as an antiseptic and disinfectant, then to other medical uses of iodine e.g. as a radiocontrast agent for medical imaging such as CT scans and X-ray imaging. There are also various other chemical uses of iodine - both historical and current. Common examples include the traditional photographic chemical silver iodide.
Iodine Uses within the Human Body
Iodine is a "trace element" meaning that modern science and medicine consider iodine to be essential for the healthy maintenance of life. The single most important use of the element iodine in animal biology - which of course includes human biology, is for the formation of two hormones in the thyroid gland (which is an endocrine gland). The hormones are thyroxine (sometimes called T4) and triiodothyronine (sometimes called T3). T4 and T3 contain four and three atoms of iodine per molecule, of hormone respectively.
Formation of Thyroxine and Triiodothyronine:
The thyroid gland absorbs iodide from the blood to form these hormones from the amino acid tyrosine. They are then stored prior to release into the bloodstream in an iodine-containing protein called thyroglobulin. The production and release of hormones T3 and T4 by the thyroid gland is regulated by another hormone called thyroid stimulating hormone (TSH), which is produced by the pituitary gland located in the head.
Why do these matter ?
The thyroid hormones thyroxine and triiodothyronine perform several important functions including regulating the body's basal metabolic rate (BMR), which determines the amount of energy the body uses, just to ‘tick over’. Therefore insufficient or excess quantities of these hormones can lead to weight-related as well as many other health-issues.
Iodine Uses as an Antiseptic and Disinfectant
- Disinfectant (e.g. for Water Treatment):
Iodine has been used to disinfect water for almost 100 years. Use of iodine for water purifcation has advantages and disadvantages compared with use of chlorine for disinfecting water, e.g. comparisons re. convenience, effect on the taste of the water and short/long-term safety. Neither of these chemicals kills all harmful bacteria and iodine should not be used to treat water for use by anyone with an allergy to iodine, with active thyroid disease or who is or may be pregnant. Examples of iodine-based preparations used to disinfect water incl. iodine topical solution, iodine tincture, Lugol's solution, povidone-iodine and tetraglycine hydroperiodide - some of which are better known by their commercial registered tradenames.
- Domestic cleaning products:
Iodine is used in many household cleaning products available from well-known supermarkets.
- Medical / Pharmaceutical:
Iodine has been used in topical disinfectant preparations for cleaning wounds (see picture above-right), sterilizing skin before surgical/invasive procedures and similar for many years.
Examples of the historical uses of iodine for medical applications include its issue to military personnel in WW1 and WW2. Iodine was made available in phials (see picture below-right) and used in field hospitals.
Iodine Uses in Modern Medicine
- Medical / Pharmaceutical: Iodine is still used in topical medical disinfectants in modern hospitals, though generally as an ingredient within commercially prepared products in order to control the concentrations of the chemicals involved.
- Lugol's Solution: An example of an iodine-based product that has been widely used in medicine is Lugol's iodine (developed by French physician Jean Guillaume Auguste Lugol in 1829 ). This consists of 5 g iodine (I2), 10 g potassium iodide (KI) and enough distilled water to form a brown solution total volume of 100 mL. Uses of Lugol's Solution have included testing for starches in organic compounds, as a cell stain to make cell nuclei more visible, application to the vagina and cervix during colposcopy - to distinguish normal from "suspicious" tissue - called Schiller's Test, to stain/indicate the mucogingival junction in the mouth, to observe how a cell membrane uses osmosis and diffusion, and to help rid the animals of unwanted parasites and harmful bacteria.
- X-ray Radiocontrast: Radiocontrast agents are chemicals used to improve the quality and hence usefulness of images - usually of internal bodily structures - obtained using X-ray based imaging techniques e.g. Computed Tomography (CT) or Radiography (X-ray imaging). Radiocontrast agents are usually compounds of either barium or iodine.
Examples of iodine-based radiocontrast agents incl. iopamidol (Isovue 370), iohexol (Omnipaque 350), ioxilan (Oxilan 350), iopromide (Ultravist 370) and iodixanol (Visipaque 320).
- Food supplement (nutrient): Due to the human body's need for a certain amount of iodine - see "Iodine Uses within the Human Body" above, iodine is sometimes added to food products e.g. some tablesalts to increase the likelihood of consumers receiving sufficient iodine through their diet. Note that serious ill-health effects can also result from excessive iodine in the body; the body needs to receive an ideal or "optimum" amount of iodine- not as much as possible.
Other Uses of Iodine in Biology
- Lugol's Solution: As mentioned above.
- To test for starch: A standard test for starch uses iodine.
Because iodine is not very soluble in water the first step is to form an iodine reagent by dissolving iodine in water in the presence of potassium iodide, resulting in a linear triiodide ion complex - which is soluble and yellow/orange in colour.
To use this to test an unknown sample to find out if it contains starch simply add a drop ofthe orange triiodide ion complex to a small volume of the other sample / suspected starch (usually in solution in a test-tube or directly onto a moist surface e.g. of a potato). If starch is present in the sample it reacts with the triiodine complex to forming a product that has a deep blue/black colour. If no starch is present then there is no colour change so the yellow/organe linear triiodide ion complex is usually still visible.
Other Iodine Uses (incl. uses of iodine combined with other elements to form iodine compounds)
- Photographic Films: Iodine was used the manufacture of chemical compounds used in traditional photography (e.g. silver iodide which is a light sensitive material used in film). This use relates only to photographs taken using old-fashioned "film" techniques and not to modern digital photography e.g. as used to take photographs or save images using mobile telephones or webcams.
- Food Colouring: The organoiodine compound erythrosine (C20H6I4Na2O5) is also known as Red No.3, E127 and by other synonyms. It is used as a food colouring agent as well as in printing inks, as a biological stain, and as a dental plaque disclosing agent.
For more information about iodine see the main page about iodine element.