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From:	Clo (t150.virl.bc.ca)
Subject:	Re: soy and thyroid problems
Date:	October 4, 2005 at 1:18 pm PST

In Reply to: soy and thyroid problems posted by Angie on October 3, 2005 at 6:26 pm:

From this board last year:

From: ron (67-21-168-234.stmnca.adelphia.net)
Subject: soy and hypothyroidism
Date: April 27, 2004 at 2:02 pm PST

For those of you who are concerned about the possible negative impact of soy on the thyroid -- I have been taking Synthroid for an under active thyroid for many years(years before I started consuming soy products). For the last couple of months I have been eating about 4 ounces of tempeh six nights a week with dinner, as well as miso several nights a week. For a couple of years before that, I was eating tofu on an almost nightly basis.

I just got the results from my blood test and my levels, according to my Dr., were exactly where they should be. In other words my soy consumption had no affect whatsoever on my thyroid levels. My Synthroid prescription level is the same as it was twenty years ago.

Here's a Q and A from http://www.drfuhrman.com/ ,Dr. Joel Fuhrman’s website (author of “Eat to Live”):

Q: I've recently read that walnuts, soy products and high fiber foods are contraindicated to the efficacy of synthroid. I am hypothyroid, take .75/day, and all of those foods are a significant part of my diet. What, if any, foods effect the thyroid in this way?

A:
The relationship between certain high fiber foods and binding of the drugs in the digestive tract inhibiting absorption of thyroid replacement therapy is slight. The PDR (Physician's Drug Reference) recommends avoiding such foods at the exact time of taking the medication; however studies of those who take the medication with a meal compared to those who did not showed such a small difference that doctors don't usually bother even mentioning it. There was one case reported in the medical literature of a person who had to
Increase the dose of her Synthroid because she took it at the same time as her high
protein soy shake each morning. To sum up, it is not important, but if you can take your medication an hour before a meal or at bedtime and see if you can get by with a hair less, but I doubt it, especially because you are taking such a low dose already. JF

From By Virginia Messina, MPH, RD & Mark Messina, PhD
(see their websites at http://vegrd.vegan.com/ and http://www.olympus.net/messina/)

Soyfoods and Thyroid

Many foods contain goitrogens, compounds that interfere with thyroid function (and in extreme cases can cause an enlarged thyroid, called a goiter). Along with soyfoods, millet, cruciferous vegetables and other foods contain goitrogens. Generally, these foods cause problems only in areas where iodine intake is low since this mineral is important for thyroid function. The effects of iodine deficiency can be made worse if the diet is high in goitrogens.

Although a concern about soy and thyroid function may be news to many vegans, it has actually been a focus of research for more than 70 years. 6 Between 1951 and 1961, this research took on a special importance when about 10 cases of goiter were diagnosed in infants who had been fed infant formula made from soy flour. These old studies form some of the basis for arguments that soy is dangerous for infants. However, the situation for today's soy formula-fed infant is very different. Since the 1960's, soy-based infant formula has been made from soy protein isolate (which does not contain the goitrogens component; soy flour formulas did) and it is fortified with iodine. No cases of goiter have been diagnosed in infants fed this formula in the past 40 years.

Nor is there any evidence that consuming soy causes thyroid problems in healthy, well-nourished people who have adequate iodine in their diet. . 7-10 However, it is possible that eating a diet with generous amounts of soyfoods could be a problem for people whose iodine intake is marginal. And that might just include some vegans, since the main sources of iodine in western diets are fish and milk. But the appropriate response to this is not to limit healthful soyfoods; it's to get enough iodine. Vegetables have varying amounts of iodine depending on where they are grown. In some parts of the world--specifically northern Europe--vegans may have low intakes of iodine. Foods that can supply iodine to vegan diets are sea vegetables, although contents vary quite a bit. Fortified foods are also a good source. Iodized salt is about the most reliable source. Vegans should be sure that, when they season foods with salt, it is iodized. If this isn't a regular part of your diet, use an iodine supplement.

CONCLUSION: Soyfoods may contain goitrogenic compounds as do other foods. There is no evidence that eating soyfoods regularly causes thyroid problems in people who eat a balanced diet. Vegans should make an effort to include adequate sources of iodine in their diet.

Three recent human studies confirm that soy consumption does not harm thyroid function. Rates of hypothyroidism are not higher In Asian countries with a soy-rich diet versus Western countries. The FDA has not issued any warnings for soy consumption and adverse health effects.

1. J Med Food. 2003 Winter;6(4):309-16. Isoflavone supplements do not affect thyroid function in iodine-replete postmenopausal women. Bruce B, Messina M, Spiller GA.

2. J Clin Endocrinol Metab 1999 Jan;84(1):192-7. Soy isoflavones exert modest hormonal effects in premenopausal women. Duncan AM, et al.

3. J Clin Endocrinol Metab 1999 Oct;84(10):3479-84. Modest hormonal effects of soy isoflavones in postmenopausal women. Duncan AM, et al.

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