Iodine and Thyroid Function

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Iodine and Thyroid Function

_http://www.vegansociety.com/food/nutrition/iodine.php_

(http://www.vegansociety.com/food/nutrition/iodine.php)

_http://www.all-creatures.org/health/iodineandthy.html_

(http://www.all-creatures.org/health/iodineandthy.html)

Iodine is vital for good thyroid function, which in turn is essential for

health. Iodine deficiency during pregnancy and early infancy can result in

cretinism (irreversible mental retardation and severe motor impairments). In

adults low iodine intake (or very high intakes) can cause hypothyroidism.

Hypothyroidism can manifest as low energy levels, dry or scaly or yellowish

skin,

tingling and numbness in extremities, weight gain, forgetfulness, personality

changes, depression, anaemia, and prolonged and heavy periods in women.

Goiter, an enlarged thyroid gland visible between the Adam's apple and the

collar

bone, is often present. Hypothyroidism can also cause carpal tunnel syndrome

and Raynaud's phenomenon. Hypothyroidism can lead to significant increases in

cholesterol levels and homocysteine levels is implicated in about 10% of

cases of high cholesterol levels. Correcting hypothyroidism can lead to a 30%

drop in cholesterol and homocysteine levels.

An iodine intake of less than 20 micro grams (µg) per day is considered

severe deficiency, 20 -50 µg/day is considered moderate deficiency and 50-100

µg/day is considered mild deficiency.

Iodine is typically undesirably low (about 50 micrograms/day compared to a

recommended level of about 150 micrograms per day) in UK vegan diets unless

supplements, iodine rich seaweeds or foods containing such seaweeds (e.g.

Vecon) are consumed. The low iodine levels in many plant foods reflects the low

iodine levels in the UK soil, due in part to the recent ice-age. About half the

iodine consumption in the UK comes from dairy products. In the US iodised

salt is widely used and some other foods are fortified with iodine. In Canada

all table salt is iodized. The UK has no iodine fortification strategy for

plant foods or salt.

Low zinc intakes exacerbate the effect of low iodine intake. Some otherwise

healthful foods contain goitrogens - substances which can interfere with

iodine uptake or hormone release from the thyroid gland. These foods are

generally only a concern if iodine intake is low. Consumption of brassicas,

such as

cabbage, Brussels sprouts, broccoli and cauliflower, increase the requirements

for iodine, especially if consumed raw. Soy beans, raw flaxseed, cassava

(used in tapioca), sweet potatoes, lima beans, maize and millet also increase

the requirements for iodine.

It is important not to over-consume iodine as it has a relatively narrow

range of intakes that reliably support good thyroid function (about 100 to 300

micrograms per day). Someone consuming large amounts of iodised salt or

seaweeds could readily overdo it. Excessive iodine has a complex disruptive

effect

on the thyroid and may cause either hypothyroidism or hyperthyroidism, in

susceptible individuals, as well as increasing the risk of thyroid cancer.

Hyperthyroidism may also occur, particularly in elderly people, due to long

term

slight iodine deficiency as this may result in additional nodules on the

thyroid.

Hyperthyroidism may manifest as an enlarged thyroid (goiter), heart rate

irregularities, tremor, sweating, palpitations, nervousness and increased

activity and eye abnormalities. Some individuals deliberately take kelp to try

to

lose weight by over stimulating the thyroid. This is a dangerous practice.

Subclinical hypothyroidism, with raised thyroid stimulating hormone (TSH)

levels but mild or absent overt symptoms, has been found to be more common

among vegans than the general population. Most vegans have low iodine intakes

but

a significant minority consume excessive amounts of iodine from seaweed,

particularly kelp. Both low and excessively high iodine intakes in vegans have

been linked to elevated TSH levels.

The key to good thyroid function is adequate, but not excessive iodine

intake. Intakes in the range 100-300 micrograms per day are desirable, though

intakes up to 500 micrograms per day are probably not harmful. If taking

supplements go for about 100-150 micrograms per day, to give a total intake of

150-200 micrograms per day. The supplements supplied by The Vegan Society

contain

an average of about 150 micrograms, so one a day provides about the right

amount. Many kelp supplements contain higher levels and should be restricted to

two a week.

If using seaweeds as an iodine source it is best to use seaweeds that have

been found to have a fairly consistent iodine content, such as kelp (kombu).

Consumption of more than 100g/year (by dried weight) of most seaweeds carries

a significant risk of thyroid disorder due to iodine intakes in excess of

1000 micrograms per day.

Nori is low in iodine and several sheets a day can be eaten without any

concern about excess iodine. Frequent addition of small amounts of powdered or

crumbled seaweed to stews or curries while cooking, or to other foods as a

condiment, is an excellent way to provide adequate iodine (in the absence of

other supplementation) and is a healthful practice for vegans. 15g of dried

kombu

or kelp in a convenient container in the kitchen provides one year's supply

for one person.

Most vegans know that B12 deficiency can cause neurological complications

and tingling sensations or numbness. B 12 deficiency is also a common cause of

elevated homocysteine levels in vegans. It should be noted that

hypothyroidism (myxedema) can also cause nerve damage, tingling sensations and

elevated

homocysteine and should be considered as an alternative diagnosis for these

symptoms.

Advice on how to check for goiter:

_www.aace.com/public/awareness/tam/2006/pdfs/NeckCheckCard.pdf_

(http://www.aace.com/public/awareness/tam/2006/pdfs/NeckCheckCard.pdf)

(http://www.aace.com/pub/tam2003/thyroid/NeckCheck2003BW.pdf)

¬?(Please note that this check card is in PDF format, so you will need a PDF

viewer such as _Adobe Acrobat_

(http://www.adobe.com/products/acrobat/readstep2.html) installed on your

computer).

Thyroid function can be readily tested by doctors based on a blood sample

and measurement of thyroid related hormone levels.

Information courtesy of Stephen Walsh