I've heard that iodine water treatment tablets can have negative side effects.
Is this true?
If so, what are some healthier alternatives?
However I seriously question that 1100 mcg number because people in Northern Japan have been found to consume over 80,000 mcg per day due to a diet high in sealife (mainly seaweed) and they appear to be living just fine.
It's clearly an issue if you are allergic to iodine.
If you already have a thyroid condition, too much iodine can complicate treatment.
Okay, so here goes:
Purification guidelines are 0.5 mg/L. Let's assume you need four liters per day (someone can comment a better guideline for water quantity, but I normally drink about four per day when hiking)
2 milligrams = 2000 micrograms. So yeah, that would exceed the 1100 UL dosage limit. However if you consider the people of northern Japan to be evidence that the real limit is much higher, then you are in no danger from this dosage.
A note on all of this: Everything I can find (CDC, webmd, etc) falls along the lines of "It's probably safe, but we're not sure and it may cause these issues".
You're extremely unlikely to manage to poison yourself unless you just nom the tablets (a couple thousand of them). Poisoning occurs in grams, several orders of magnitude more than what is used to purify water. To poison yourself, you'd need to consume ~2000L of iodine purified water in a short period, at which point iodine is no longer your primary concern.
Well it's been banned for sale in Europe for use in purifying water. (http://www.grough.co.uk/magazine/2009/08/13/eu-ban-will-end-walkers-use-of-iodine) As that webpage mentions Chlorine is an alternative, but leaves a nasty taste (although I believe you can add another chemical to neutralise the taste)
Alternatives are a water filter, or UV light serialisation.
Pretty much all water tablets I've seen have been chlorine based here in the UK - I've used them on a number of occasions. In normal doses they don't affect the taste that much, and they have the advantage for people who don't know what they're doing that if they really overdose on the tablets the water will taste too foul to drink anyway!
If you don't want to use tablets or affect the taste at all, then hold the water at a rolling boil, and if necessary use a ceramic filter to remove any nasty metals that may be present. It's more hassle than just using tablets but the way to go if you don't have them or don't want to use them!