Remember when vitamin D was the overlooked nutrient?
Thanks to a wide publicity for new findings, awareness has risen and the US RDA got raised in 2010.
Like vitamin D, iodine exerts exceptionally broad and beneficial effects in the body … and it's in need of renewed attention.
A number of signs suggest that women are at higher risk for inadequate intake … and for iodine-related health problems.
Iodine matters – especially to women – more than most know
Without enough iodine you can't make enough thyroid hormone … which regulates metabolism, body temperature, muscle growth, and much more.
|Iodine in seafood|
Seafood is the richest source of iodine, though levels can vary widely by region and seasons.
These are the average iodine levels in some common ocean foods, per 3 oz. serving.
Note: A microgram (mcg) is one-thousandth of a milligram (mg).
- Wakame seaweed (dried) – 3,528 mcg
- Oysters – 137mcg
- Mussels – 110mcg
- Prawns – 110mcg
- Cod – 99mcg
- Salmon – 60mcg
- Halibut – 44mcg
- Mackerel – 40mcg
- Shrimp – 35mcg
- Sardines – 20mcg
- Tuna – 17mcg
Lack of thyroid hormone can lead to goiters, fatigue, weight gain, muscle weakness, constipation, and breast cysts or tenderness.
And studies link low iodine levels to higher rates of breast cancer, stomach cancer, and heart disease … while low iodine levels may trigger or aggravate chronic fatigue syndromes.
Why does this link to such a long list make sense?
As a current “Bible” of endocrinology – Lewis E. Braverman, M.D.'s textbook The Thyroid – notes, iodine is critical to the eyes, prostate, breasts, and ovaries.
Surprisingly, just one-third of the body's total iodine goes to the thyroid gland.
The remainder goes to other tissues, where it exerts anti-inflammatory, antioxidant, and non-proliferative (anti-cancer) roles unrelated to its role in thyroid-hormone production.
Iodine and breast health
Compared with their American peers, Japanese women consume much more iodine – from seafood and seaweed – and they're about two-thirds less likely to get breast cancer.
Ocean foods also provide Japanese women with far more selenium than their American peers, and that mineral acts synergistically with iodine to support thyroid health.
Breast carcinomas usually develop in ductal tissues normally high in iodine. And when they're iodine-deficient, these ductal tissues become more sensitive to estrogen's tumor-promoting properties.
Interestingly, iodine levels rise in breast tissue when women are lactating, a
How much iodine is enough?
Public health authorities define “adequate” as a median urinary iodine levels of 100–199 mcg/L in children and adults, 150–249 mcg/L in pregnant women and more than 100 mcg/L in lactating women.
Levels in children and non-pregnant adults below 100 mcg/L are deemed insufficient, and severe iodine deficiency is defined as a urine level below 20 mcg/L.
As happened with vitamin D, new research suggests that official U.S. definitions of “adequate” iodine intake aren't high enough to ensure optimal health.
Allowances (RDAs) for Iodine
Note: A microgram (mcg) is one-thousandth of a milligram (mg).
Ages 1 to 8 – 90mcg
Ages 9 to 13 – 120mcg
Ages 14 and over 150mcg
Pregnant women* – 220mcg
Nursing women – 290mcg
*The World Health Organization, UNICEF, and the International Council for the Control of Iodine Deficiency Disorders (ICCIDD) recommend 250 mcg per day for pregnant women.
nd women with breast cancer have lower-than-average iodine levels in their breast tissue.
While diets high in iodine (or selenium) aren't proven to prevent or treat breast cancer, substantial evidence suggests that iodine-poor diets – and officially “sufficient” body levels – can be risk factors.
A new shortage … especially in women
Most Americans get enough iodine to avoid outright deficiency, as defined by official U.S. standards.
But – as with vitamin D – many iodine researchers question the adequacy of current intake recommendations.
(See our sidebar, “How much iodine is enough?”.)
Although the most recent national nutrition survey found that average iodine intake in the U.S. was adequate by official standards, certain groups – especially women – were barely sufficient or outright deficient in iodine.
Notably, iodine intakes among pregnant women are often deficient or slightly “sufficient” (an arguable point at today's rather low U.S. RDAs), with a median level of just 125 mcg/L vs. the recommended 150mcg/L.
The widespread iodine shortage in pregnant women holds serious implications for mothers and their babies … see “Growing Brains Lack Iodine”.
Iodine deficiency appears to be on the rise again, especially among women … often goes undiagnosed, thanks to the many possible causes of its typical symptoms:
- Dry skin
- Puffy face
- Weight gain
- Thinning hair
- Cold sensitivity
- Muscle weakness
- Slowed heart rate
- Impaired memory
- Elevated cholesterol level
- Joint pain, stiffness, or swelling
- Heavier or irregular menstrual periods
- Muscle aches, tenderness, and stiffness
Iodine deficiency was common in the early 1900s, until iodine was added to table salts and used to make dairy and baked goods.
Unfortunately, Americans' average iodine levels fell by half from the 1970's to the 1990's – from 320 mcg/L to 145 mcg/L – and have never rebounded.
Some of this decline resulted from substantial drops in the iodine content of dairy and baked goods, due to new production methods … along with common use of iodine-blocking bromides in commercial baked goods since the early 1990's.
Researchers also blame long-standing (mostly misguided) public health advisories to reduce salt and egg intake for blood pressure and cholesterol control, and a substantial drop in the use of iodized salt in packaged and prepared foods.
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