Life Extension Magazine October 2009
Halt on Salt Sparks Iodine Deficiency
By William Davis, MD
Those who consume heavily salted foods suffer an increased incidence of certain cancers.1,2 In susceptible individuals, high sodium intake spikes blood pressure.
In response to the dangers of consuming excess salt, Americans are restricting their sodium intake. This has led to a risky unintended consequence.
Typical Western diets are low in iodine. When iodized table salt is reduced, people can easily become iodine insufficient or deficient.
Inadequate iodine not only impairs thyroid function, but is also linked to increased risks of breast cancer and fibrocystic breast disease, along with fatigue and weight gain.
Fortunately, iodine is such a low-cost element that more of it can be added to multi-nutrient formulas that health-conscious individuals take each day.
Widespread Iodine Use Eliminates Goiter Epidemic
Most Americans over 60 years old remember the days of goiters, the unsightly thyroid gland enlargement visible on the neck that was wildly rampant. As many as one-third of the inhabitants of some parts of the country were affected.
Goiters were not just unattractive. They sometimes reached grotesque proportions, compressing adjacent structures like the trachea, necessitating surgical removal. If a pregnant woman had goiter, she was at risk for delivering a mentally impaired child.
The connection between goiter and deficiency of the trace element iodine was confirmed when a family doctor conducted an experiment on schoolgirls in 1916. Despite objections from local residents, Dr. David Marine administered what we now recognize as a very large dose of iodine: 170-340 mg (170,000 -340,000 micrograms or mcg) sodium iodide per day for a period of 10 days, repeated every 6 months for 2.5 years. Of the 900 girls with normal thyroids who received iodine supplementation, virtually none developed goiters, compared to 28% of the control group not receiving iodine.3,4
Recognition of iodine’s importance launched it into the realm of public health, felt to be too important an issue to leave to individuals, families, or physicians to remedy on their own. With no TV, radio, or internet, and much of the country rural or illiterate, how could the US ensure iodine intake nationwide? In 1924, the FDA introduced a voluntary program for adding iodine to table salt.5
From the 1950s to the 1970s, most Americans willingly complied by liberally shaking the salt shaker over anything and everything. Overt iodine deficiency largely became a thing of the past, and goiters became a rarity. By FDA guidelines, approximately one half teaspoon of iodized salt per day, or 3,000 mg (containing 1,150 mg sodium), provided the Recommended Daily Allowance of iodine of 150 mcg per day (the RDA is higher for pregnant or lactating women).6
Following the widespread application of the salt shaker was the recognition of the dangers of hypertension. Sodium from salt increased blood pressure and fluid retention in susceptible individuals.7 As a result, after goiter had been erased from the consciousness of most Americans, the public health message reversed and urged reduced use of salt. Salt use was demonized as the cardiovascular dangers of hypertension gained public recognition.
In the 21st century, many health-conscious people proudly declare their assiduous avoidance of salt, especially iodized table salt. Others have turned to alternative preparations, such as sea salt (containing very little iodine content), Kosher salt (containing no iodine), or potassium chloride-based salt substitutes (containing no iodine).
Iodine Has Been Forgotten
The public health message to limit salt use underlies a gradual and insidious return of iodine deficiency. The National Health and Nutrition Examination Surveys (NHANES) assessment of Americans’ health revealed a 50% reduction in iodine levels and a quadrupling of iodine deficiency in the period between 1971 and 1994. Twelve percent of the population surveyed from 1988 to 1994 were severely iodine deficient, judged by urinary levels of iodine.8 Women of childbearing age are at particular risk for iodine deficiency, with up to 36% evidencing low levels.9
Even goiters are staging a comeback. In my cardiology clinic, I now see about two or three patients with small to moderate goiters every day. So history repeats itself.
Your Iodized Salt Isn’t So Iodized
If you rely on iodized salt for iodine, are you really meeting your body’s iodine needs?
A recent detailed analysis of several brands of commercially available salt showed that, after opening, iodine is lost rapidly from the product. Once the container is exposed to air, iodine content is nearly gone within four weeks after opening (even faster under conditions of high humidity). The study suggests that, even among people who use the salt shaker frequently for cooking and food, daily iodine intake may be below the recommended daily intake.10
The majority of salt used in processed foods is not iodized. While dairy products and baked foods (bread and related products) were formerly substantial sources of iodine, the iodine content of these foods has dropped due to changing practices by dairy producers and bakers.10-12
There’s no question that iodized salt worked to stop goiters during a time when the entire family liberally used salt, causing mothers to buy another canister every couple of months. But with modern efforts to reduce salt, a single canister can last 6 months or longer—completely devoid of iodine.
Does No Goiter Mean Perfect Thyroid Health?
How much iodine is necessary for ideal health? Over the years since iodine and thyroid disease have been connected, the absence of goiter has been used as the index of iodine adequacy. Goiter suggests inadequate iodine; no goiter means sufficient iodine. (Note: While most goiters suggest low iodine, other conditions can occasionally be at fault, such as the overactive thyroid of Graves’ disease.)13
Twentieth century overuse of iodized salt led to complacency. Since iodized salts erase most goiters, medical professionals and the pubic mistakenly believed they knew what they needed about iodine. But does alleviating goiter also mean that thyroid function is optimized? If goiter represents the visible manifestation of hypothyroidism, is there an intake of iodine that can further improve thyroid function, even after goiter is reversed or suppressed?
The current RDA for iodine of 150 mcg per day for non-pregnant adults is indeed sufficient to prevent or reverse goiter. Iodine intake below the RDA over months to years leads to a thyroid gland that enlarges, or “hypertrophies,” an attempt to overcompensate by growing larger and thus better able to extract the little iodine available from the blood. If iodine deficiency continues, production of thyroid hormones, T3 and T4, begins to suffer, and hypothyroidism (low thyroid hormone levels) ensues. To counterbalance this, the pituitary gland produces higher levels of thyroid-stimulating hormone (TSH); TSH increases the production of T4—sometimes back to normal levels early on—and also stimulates thyroid growth.14
The Japanese provide some unique insights into higher intakes of iodine. Japanese consume a variety of foods from the ocean, including iodine-rich seaweeds like kelp and nori. Even foods grown in Japanese soil, such as fruits and vegetables, have iodine content several-fold higher than in most other parts of the world.15
Estimates of Japanese iodine intake vary widely, with values ranging from 378 mcg to as high as 13,800 mcg per day. The extraordinary range is partly due to the variable consumption of iodine-rich seaweeds.15-18 Because of the wide variation, Japanese researchers have argued that a “typical” Japanese intake of iodine is impossible to determine, though it is clearly several-fold higher than that of Americans.
Some authorities argue that greater iodine intake is responsible for the reduced incidence of fibrocystic breast disease, breast cancer, and thyroid disease in Japan.19 The evidence for a connection between iodine and fibrocystic breast disease is strongest.
Is the Japanese intake of iodine closer to “ideal”? If the RDA for iodine of 150 mcg yields some improvement of thyroid measures, would 300 mcg, 900 mcg, 10,000 mcg, or even 50,000 micrograms further improve thyroid function or overall health? There are proponents of very high doses of iodine with claims of extravagant results; however, the data have not yet been formally published. Unfortunately, studies examining these iodine doses have not yet been performed in the modern era using current methods. However, experiences
like those of the Japanese argue that the ideal dose of iodine is much greater than the current RDA in the United States.
Despite nearly 90 years of public health efforts, we are left with the impression that there are many stones yet unturned in the area of iodine and its role in health. The optimal dose of iodine for health appears to be among these unsolved mysteries