I use Listerine.  Rinse first to soften the tarter, then brush with Oral B electric toothbrush super sonic.  The $15 ones at the supermarket.  At 73 I still have all my teeth.  While a blood test can measure iodine levels, it's not the most accurate method for assessing iodine status, and urinary iodine excretion is considered a better indicator.  Have any of your dermatologists ever done a biopsy for dermatitis herpetiformis?  I may have missed it.  Note the similarity of Casal's necklace to one of your symptoms. Pellagra rash is a characteristic skin manifestation of niacin (vitamin B3) deficiency. It typically presents as:  Erythema: Red, sunburned-like areas of skin, often on the face, neck, arms, and legs.  Scaliness: Dry, flaky skin that may become thickened and crusty.  Hyperpigmentation: Darkened patches of skin, particularly in sun-exposed areas.  Casal's necklace: A dark, pigmented band around the neck.  I am currently taking these} Vitamin D 10,000 IU (250 mcg) DHEA 100 mg 500 mcg Iodine  10 drops of Liquid Iodine B1 Thiamin 250 mg  B2 Riboflavin 100 mg B3 Nicotinic Acid 500 mg 4 times a day for hyperlipidemia. B5 Pantothenice Acid 500 mg Vitamin C 500 mg     Selenium 200 mcg  Several times a week

I will. Thanks. I did just have mg B12 drawn. I should also state that I am already taking a Vit D supplement, as I live in the US in New England sand just about everyone who lives here is deficient, esp during our winters with less exposure to natural sunlight. I was also taking a chewable bariatric vitamin as well because of my food issues related to my cancer treatment (which was many years ago, but there are long term effects.) I just stopped it because I was unable to get any gluten information about it. And it did contain iodine. Is there even a vitamin that doesn’t? I don’t know, but I will check. I also take Calcium and Magnesium in the form of “Rolaids” for leg cramps/spasms, with good effects. Thanks. 

@Itsabit, Ask your doctor for an erythrocyte transkelatose test to measure thiamine.  It's a better measure of thiamine deficiency than a serum test.

Most toothpastes are naturally gluten-free, but this article may be helpful:  

This article has some detailed information on how to be 100% gluten-free, so it may be helpful (be sure to also read the comments section.):