Does iodine deficiency contribute to plaque growth?
Background and interview with Dr. Stephen Hoption Cann
Thyroid status is proving to be a crucial facet of
the Track Your Plaque program.
In this Special Report we review iodine’s neglected role in thyroid
health, and thereby heart health. This is supplemented by an interview
with epidemiologist, trace mineral
and iodine expert, Dr. Stephen Hoption Cann.
Dr. Hoption Cann is author of the 2004 paper,
Hypothesis: Dietary Iodine Intake in the Etiology of Cardiovascular
Disease
In this important paper, Dr. Hoption Cann reviews the several decades of
obscure - and much forgotten - clinical and scientific literature that
makes a compelling argument for the critical connection between iodine
and heart health.
Before we turn to Dr. Hoption Cann’s important observations, let’s
discuss some background on iodine.
Iodine: Disinfectant, antioxidant, essential nutrient . . . coronary
preventive agent?
Iodine: Yes, the same peculiar purple-brown liquid your mother applied
to a scraped knee. Mom knew of iodine’s anti-infective properties. But
perhaps she was unaware of its potent anti-oxidative properties, its
ability to sterilize drinking water, its radio-opaque quality (making it
suitable for use as a contrast agent for x-ray), its necessity for
thyroid function.
Paleontologists believe that iodine was the first protective
anti-oxidant employed by primitive organisms exposed to the developing
oxygenated world. Iodine became concentrated in the oceans, providing
iodine to coastal regions. Areas away from the coasts, or never covered
with oceans, contain little or no iodine. There is even a fascinating
theory that Neanderthals were an iodine-deficient inland form of primate
that resemble modern iodine-deficient humans, or “cretins”; the survival
disadvantage of iodine deficiency permitted iodine-replete (due to
better access and a theorized genetic alteration that made iodine
retention more efficient) coastal primates (now called “early modern
humans,” formerly “Cro-Magnon”) to replace Neanderthals. The ability to
gain access to and efficiently retain iodine may therefore have played a
crucial role in human evolution.
Turn-of-the-last-century America was plagued with goiter, an unsightly
enlargement of the thyroid gland visible on the front of the neck. As
many as a third of the inhabitants of some parts of the country (e.g.,
the Great Lakes, AKA the “goiter belt,” and much of the Midwest) were
affected. The connection between goiter and deficiency of iodine wasn’t
made until a family doctor in Cleveland, Ohio, conducted a homespun
experiment on schoolgirls in a nearby community 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, mcg) sodium iodide per day to 900 girls. Virtually
none of the girls receiving iodine supplementation developed goiters,
compared to 22% of the control group not receiving iodine (Zimmerman MB
2008).
Mothers from the same era, often deficient in iodine, gave birth to
severely impaired babies afflicted with far below average intelligence,
consigned to a brief, disabled life. These children were known by the
harsh name of “cretins,” the disease known as “cretinism.”
The recognition of the importance of iodine launched it into the realm
of public health, too large an issue to leave to individuals, families,
or physicians to remedy on their own. Much debate ensued in the
mid-twentieth century on how to best ensure that the U.S population
receive a minimum quantity of iodine in their diets. Table salt (sodium
chloride) became the agreed vehicle for iodine in 1924, though
iodization was deemed voluntary, not mandatory.
During the 1960s and 70s, most Americans willingly complied by liberally
shaking the salt shaker over anything and everything. Overt iodine
deficiency largely became a thing of the past, goiters a rarity. FDA
guidelines suggest iodine content in salt of 45 mg/kg; this means that
slightly over one half teaspoon of salt per day, or 3000 mg (1,150 mg
sodium), provides the Recommended Daily Allowance of iodine of 150 mcg
per day.
Coincident with the widespread application of the salt shaker was the
recognition of the dangers of hypertension. Clinical studies made it
clear that liberal use of salt increased blood pressure, fluid
retention, even osteoporosis.
The public health message reversed its focus and began to urge reducing
use of table salt. Salt use was demonized as the cardiovascular dangers
of hypertension gained public recognition. Somehow, the issue of iodine
was forgotten. (This has created some peculiar public health collisions.
While the American Heart Association advises reduction of salt use, and
the American Medical Association has even urged the FDA to remove salt
from the “generally recognized as safe” designation, others like UNICEF
and the charitable International Council for the Control of Iodine
Deficiency Disorders both advocate for increased salt use worldwide.)
Fast forward to the 21st century and many health-conscious people
proudly declare their assiduous avoidance of salt, certainly iodized
table salt. Others have turned to alternative preparations of sodium
chloride, such as sea salt (very little iodine content), Kosher salt (no
iodine), and potassium chloride-based salt substitutes (no iodine).
So what’s become of the iodine?
Maybe your iodized salt isn’t so iodized
Even people who use iodized salt are getting less iodine than expected.
Iodine deficiency is on the rise. The NHANES data of Americans’ health
has revealed a quadrupling of iodine deficiency in the period between
1971 and 1992, with 11% of the population now clinically iodine
deficient as judged by urinary levels of iodine (Hollowell JG et al
1998). Regional variation in incidence seems to have been smoothed over,
with no specific areas of the country standing out more than others,
unlike the past (likely due to the globalization of the food supply).
A recent study (Dasgupta PK et al 2008) suggests that, even among people
who use the salt shaker for cooking and food, daily iodine intake is
only around 45 mcg per day. Interestingly, a detailed analysis of
several brands of commercially-available salt showed that, after
opening, iodine is lost rapidly from the product, especially if stored
in humid conditions (see figure); within 10-20 days after opening,
iodine content is dramatically reduced, even nearly gone, under
conditions of high humidity. Their analysis also showed that, even if
the salt is labeled “iodized,” it usually contains substantially less
than the FDA-suggested 45 mg/kg.
Loss of iodine over time with exposure to air with specified humidity
levels, no light, 22 +/- 1 °C.
From Dasgupta PK et al 2008.
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, iodine content of these foods has dropped
70% over the past 20 years due to changing practices by dairy producers
and bakers (Dasgupta PK et al 2008). Add to this the currently popular
notion of “buy local” and we might therefore expect to see regions with
greater proportions of their population with goiter, much as in the
early 20th century.
In short, even people who are using iodized table salt and eat common
processed foods may not be getting the iodine content they need. In
addition, the public health message to limit salt use is accelerating a
gradual and insidious return of iodine deficiency.
Iodine deficiency is inevitably followed by underactive thyroid
function, reductions in thyroid hormone levels and hypothyroidism.
Ironically, we might predict that iodine deficiency is apt to primarily
afflict the health conscious, the people most likely to avoid salt and
follow the “buy local” practice.
So history repeats itself.
What quantity of iodine is necessary for ideal health?
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