Iodine in soils is very variable - there are many areas of the world where there is so little that residents get goitre. As a result, most countries require that table salt be supplemented with iodine. However, most do not require that foods such as cheeses be processed with iodized salt, nor that animals destined to be slaughtered for meat have iodine added to their food or salt blocks.
The result can be seen at the two food nutrient data banks that list iodine content of foods - variances by factors of up to ten even for unprocessed foods. For example, the average for unprocessed tree/shrub fruits at the Finnish National Public Health Institute Nutrition Unit (Fineli) Food Composition Database is 0.88 µg/100 g; at the Danish Institute for Food and Veterinary Research (DIFVR) Food Composition Databank it's 0.55 So for iodine, it is unrealistic to rely on individual food analyses except for natural seafoods, instead one must use averages over food groups. And, foods that have salt added during processing must be separated into those that use iodized salt or sea salt, and those that use purified salt. For example, cheeses prepared with iodized salt have iodine concentrations that average 45 µg iodine per 100 g of cheese, whereas those that use purified salt average 7 µg. Salted pork (ham) and fish will be just as variable.
I currently use and recommend the following averages, based upon Fineli and DIFVR data:
|purified foods e.g. sugar||0|
|tree/shrub fruit||0.7 µg/100 g|
|cheese (pure salt)||7.5|
|cheese (iodized salt)||45|
other notes on nutrition