Re: what are the natural sources of iodine in food and water?

Iodine was discovered by Courtois in 1811 while making gunpowder.  Some 
seaweed ash was being used from which the iodine vaporized as a violet 
vapor.  Baumann in 1895 discovered it in the human thyroid gland and it's 
necesity in the human diet was discovered shortly thereafter.  

Most of the iodine in nature resides in the ocean.  It was present during 
primordial development of the earth.  Iodine was leached from the surface 
soil by glaciers, snow and rain and was carried by wind, rivers, and 
floods into the sea.  Iodine occurs in the deeper layers of the soil and 
is found in oil-well and natural gas effluents.  Water from such deep 
wells can be a major source of iodine in the diet.  

Iodine ions are oxidized by sunlight into elemental iodine in the 
atmosphere and returned to the soil by rain.  In this way the cycle is 
completed.  However, the return of iodine to the soil is slow and small in 
amount compared to the original loss of iodine.  Natural correction of 
iodine content of the soil does not always take place.  Crops grown in 
iodine-deficient soil are also iodine deficient.  Because humans are 
dependent on crops for iodine, they too can become iodine deficient if 
they eat vegetables etc grown in iodine-deficient soil.

Iodine is present in seafoods and in foods grown in iodine rich soil.  
Dairy products are a significant source of iodine in the American diet due 
to the iodine containing chemicals used to clean dairy equipment and to 
the addition of iodine to the feed of dairy cows.  Breads, cereals and red 
candies (red dye is high in iodine) are also excellent sources of iodine.  
A significant source of dietary iodine in the western hemisphere is 
iodized table salt.  

Realizing the dangers of iodine deficiency most countries throughout the 
word now fortify their salt supply with iodine to prevent deficiency.  
Iodine was first added to the salt supply in Switzerland and in Michigan 
in the 1920's.  This was done to combat iodine deficiency.  

Over the years, iodine intake has increased due to dietary diversification 
(most people eat a greater variety of foods containing iodine) and 
globilization of the food supply.  (Most foods we eat are not grown in the 
same geographic area anymore.  So if the soil is depleat of iodine in one 
area, chances are we are eating some foods grown in areas with iodine 
repleat soil.)

I hope this answers your questions about iodine.  Please feel free to 
contact me if you need further assistance.

Loretta O'Neill, MS, RD








References:
Hetzel, B.S.: THe Story of Iodine Deficiency-An International Challenge in 
Nutrition.  Oxford, Oxford University Press, 1989.