Colloidal is a unique and special formulation of iodine. Created in the 1920s, colloidal iodine offers a more bioavailable form of iodine than typical compounds of sodium iodide or potassium iodide. If you're interested in the history of it, the creation and application for colloidal iodine was outlined in a work by WL Chandler and E J Miller in 1926.  Colloidal iodine is also known as as atomic iodine, nascent iodine, and nanocolloidal iodine. Each of these names reflects the uniqueness of this iodine form.
Typically, iodine occurs elementally as I2 or in an iodide compound, such as potassium iodide. Elemental iodine is highly toxic and caustic. Potassium iodide, as well as other iodide forms, are the way the body normally gets dietary iodine. The effort of separating iodine from potassium requires the body expend energy, making iodine absorption and use a labor intensive process. Colloidal iodine eliminates this.
Why Colloidal Iodine Works Better
Colloidal iodine eliminates the need to isolate iodine from its compound state. A solution of colloidal iodine contains isolated iodine atoms. In this state, they are inactive and neither toxic nor damaging. The body can quickly absorb and use this form of iodine.
Why You Need Iodine
Life as we know it wouldn’t exist without iodine. In humans, iodine regulates metabolism  and is integral to the formation of two of the most important thyroid hormones, T3 and T4.  These two hormones directly affect cellular metabolism and also impact the creation of other hormones.  Without adequate iodine levels the thyroid cannot maintain balanced hormone levels.
Symptoms of Iodine Deficiency
Inadequate iodine intake can lead to fatigue, the frequent feeling of being cold,  difficulty with concentration,  a reduced metabolism  and immune function . If the iodine deficient state continues, hormonal balance,  mood disorders,  and hypothyroidism  can result. Iodine deficiency during fetal development can lead to hypothyroidism, impaired fetal and childhood neural development, and in more severe cases mental retardation and neonatal and infant mortality.   Some speculation has even surfaced questioning if there's a link between iodine deficiency and autism in children. 
The Best Type of Colloidal Iodine
There's no reason to make this complicated. When looking for a colloidal iodine, look for
- A true glycerin solution. Some colloidal uses alcohol which causes a burning sensation;
- Completely non-toxic; and,
- A pure colloidal iodine without any iodides.
If you do your homework, you'll realize this criteria narrows the playing field. To make things easy, I recommend nascent iodine.
Watch an In-Depth Video on Everything You Need to Know About Iodine
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†Results may vary. Information and statements made are for education purposes and are not intended to replace the advice of your doctor. If you have a severe medical condition or health concern, see your physician.