The dangers of hot yoga – iodine loss and the thyroid


This is part of an investigation into the possible negative affects of Hot Yoga by Mark Giubarelli.


In This study we will try to measure the iodine loss from hot yoga and see if it may be detrimental to our health.


Hot Yoga has a very positive thing and this study will not affect the casual once or twice a week practitioner. It was intended as a warning for those who are practicing in a hot environment consistently over many years.


Awareness is key to health and making sure our biochemistry does not go into imbalance is essential  in that journey to health.



  1. Chooses pink Himalayan salt over iodized salt.
  2. Do not eat sea weed.
  3. Sweat a lot from hot yoga.



How Important Is Iodine?

Iodine is part of a group of elements that are also known as the halogens, fluorine,chlorinebromine and iodine all share qualities of seven electrons in their outer shell.

Fluorine chlorine and bromine are used in the absence of iodine.

Thyroid enlargement, or goiter, is one of the earliest and most visible signs of iodine deficiency. 

In 1990 The World Health Organization stated that 28.9 % of the world population had iodine deficiency.

The World Health Organization estimated that 43 million people had serious mental impairment from iodine deficiency.

Inserting proper iodine into  diet is one of the most effective ways we can prevent many mental disorders.

Iodine deficiency is recognized as the most common cause of preventable brain damage in the world.



The History Of Iodine

References to the thyroid gland and its diseases can be seen in the literature of ancient Greek, Indian and Egyptian medicine. Goiter has always been a disease of immense interest of the general population due to its widespread prevalence and noticeability.


Italian physicians of the School of Salerno were the first to report the specific use of the sponge and dried seaweed to treat goiter. In the 13th century, de Villanova cautioned the effect of the sponge on goiter was limited: it could cure goiter of recent origin in young people but had only a modest effect on large, chronic goiters.


In 1811, France was at war, and Bernard Courtois was producing saltpeter for gunpowder for Napoleon's army. He was burning seaweed to isolate sodium bicarbonate and when he added sulfuric acid to the ash, he produced an intense violet vapor that crystallized on cold surfaces. He sent the crystals to Gay-Lussac , who subsequently identified it as a new element and named it iodine, from the Greek for violet.


8 years after the discovery of iodine from seaweed, a Swiss physician, JF Coindet who previously used burnt sponge and seaweed successfully for the treatment of goiter, reasoned that iodine could be the active ingredient in seaweed. In 1819, he tested tincture of iodine Twenty drops of these solutions contained approximately 50 mg (one “French grain”) of iodine. Coindet routinely prescribed 10 drops three times a day for the first week, and then 15 drops thrice a day for the second week and 20 drops three times a day subsequently. He only rarely prescribed higher doses. The recommended duration of treatment was 8-10 weeks. Results of the treatment were spectacular: softening and shrinking of goitres occurred after 8 days, and disappearance or a significant improvement in disfiguring or uncomfortable goitres occurred later in many cases. He concluded that, used with competence, iodine would become one of the most potent medication brought to medicine by modern chemistry.


Following Coindet's enthusiastic report on the efficacy of iodine, a craze for taking iodine rapidly developed in Geneva and elsewhere. 

A well-known Geneva physicianDr. J.-P. Colladon (1769-1842), who had studied medicine in Edinburgh (and had been a strong proponent of vaccination) reported that among 9 patients he had treated with iodine, 6 had developed severe ill-effects, predominantly gastric pain and discomfort.

Following Coindet's enthusiastic report on the efficacy of iodine, a craze for taking iodine rapidly developed in Geneva and elsewhere.



The French chemist Boussingault  was the first to advocate prophylaxis with iodine-rich salt to prevent goiter. Working in Bogota, he measured iodine levels in rock and in salt deposits of the Andean region. In 1825, he reported villages in the province of Antioquia treated goiter with ‘aceyte de sal,’ an acrid, ‘marine smelling’ fluid from the salt deposits. He demonstrated in 1835 that salt sent from goiter-free Antioquia to neighboring regions reduced goiter endemia. Roulin, who worked with Boussingault in the Andes, stated goiters of young people disappeared when they emigrated to goiter-free regions and, conversely, outsiders who immigrated into areas of severe goiter developed goiter within 5–6 years. Boussingault and Roulin were the first to recommend goiter prophylaxis with iodized salt; it would be nearly 100 years before their vision was realized. Nevertheless, they did not believe lack of iodine was the cause of goiter; they suggested goiter was caused by a lack of oxygen in drinking water and was common at high altitudes in the Andes because of the reduced atmospheric pressure.



In 1883, Semon suggested myxedema was due to thyroid insufficiency and the link between goiter.

In 1896, Baumann and Roos discovered iodine in the thyroid.

In the first 2 decades of the 20th century, pioneering studies by Swiss and American physicians demonstrated the efficacy of iodine prophylaxis in the prevention of goiter and cretinism. Switzerland's iodized salt program has been operating uninterrupted since 1922.

I am satisfied. I have seen the principal features of Swiss scenery —Mount Blanc and the goiter— and now for home.




Extract from the New York Times

Dr. David Marine, a pathologist who discovered the iodine treatment for goiter and other thyroid arrived in Cleveland in 1905 with his newly earned medical diploma from the Johns Hopkins Medical School.

Dr. Marine was to recall in later years, he was immediately struck by the highly visible incidences of swollen necks indicating goiters in humans. He noticed similar swellings in dogs in the street and fish in the market.


To establish his premise, Dr. Marine, then in his late 20's, conducted one of the earliest large‐scale experiments ever attempted on humans.

He persuaded the authorities in Akron to permit him to give minute doses of iodine to 2.000 students, while 2,000 others in a control group not receiving the dosage would be closely monitored. Students in both groups were free of any thyroid problems when the test got under way.

Of the 2,000 receiving the iodine, five developed some form of thyroid condition, while 475 in the other group developed symptoms.

In 1917, his book, “The Prevention of Simple Goiter in Man,” was published. This was to remain a hallmark of his 40‐year‐long research and teaching career.

Signs and symptoms of an iodine deficiency

  • Swelling in the Neck. Swelling in the front of the neck (Goiter)
  • Unusual Weight Gain
  • Fatigue and Weakness
  • Hair loss
  • Dry, Flaky Skin
  • Feeling Colder Than Usual
  • Changes in Heart Rate
  • Trouble Learning and Remembering


Iodine Fact

Most of the daily dietary iodine intake (approximately 90 %) will be excreted in the urine.

Endocrine Laboratory, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Ireland.

How much iodine do we need?

The recommended dietary allowance (RDA) for iodine for adults is 150 mcg per day


The average American takes in 170-250 mcg/day of Iodine in their diet. Humans lose considerable amounts of Iodine in their sweat (Up to 146µg day with only moderate exercise).

Winston W. Greene, B.A., B.S., D.C.


Excess iodine intake is considered to be associated with hyperthyroidism or hypothyroidism in some vulnerable individuals.

Laurberg P, Cerqueira C, Ovesen L, Rasmussen LB, Perrild H, Andersen S, et al. Iodine intake as a determinant of thyroid disorders in populations. Best Pract Res Clin Endocrinol Metab. 2010;24: 13–27.


Iodine Fact

When cooking with iodized salt 50 to 70 % of iodine is lost. Minimum loss was found during shallow frying and maximum during pressure cooking. The duration that the iodized salt is cooked in food played an important role in it's loss therefore it is better to add the salt later when cooking if you are using it as a primary source for iodine.

The Average of Dietary Iodine Intake due to the Ingestion of Seaweeds is 1.2 mg per day in Japan.

THYROID Volume 18, Number 6, 2008 Mary Ann Liebert 


Humid environments also lead to iodine loss in iodized salt.




Effects of storage and cooking on iodized salt and study in 1999 showed the retention of iodine during cooking varied considerably from 36.6% to 86.1%.

The iodine concentration in salts varied greater from 3.0 to 100.3 mg/kg in salt for markets.


Iodine in salt may not be enough.



Even mild selenium deficiency can trigger autoimmune diseases in the thyroid.

200 mcg  of selenium a day suppresses autoimmune activity in many areas of the body including the thyroid.

Published in the Society for Endocrinology


How much do we loose in hot yoga?

The easiest way to measure your sweat rate is to weigh yourself without clothes on before hot yoga (one hour class). After the hot yoga class weigh yourself again (without clothing that has retained water). You must not  consume any fluids or use the restroom for accurate results.


A study coducted in May 2001 monitored electrolyte loss from profuse sweating in soccer team players and evaluated the relationship between this source of iodine loss and iodine deficiency. Thirteen male soccer-team players and 100 sedentary students from the same high school were evaluated for 8 days, during which the players were training. The authors analyzed 208 sweat samples to determine losses of iodine, sodium, potassium, and calcium in sweat. Excretion of urinary electrolytes by the subjects was also measured.

The mean losses of iodine, sodium, potassium, and calcium in sweat following a 1-hr game were 52 microg, 1,896 mg, 248 mg, and 20 mg, respectively; the ratios of sweat loss to urinary daily loss of the four electrolytes were 0.75, 0.2, 1.88, and 0.92, respectively.


Urinary iodine was significantly  lower than the normal level of 50 microg/gm creatinine in 38.5% of the soccer players, compared with 2% of the sedentary students.


Forty-six percent of the players had Grade I goiter, compared with a mere 1% of the sedentary students in the study.

The results of the study suggest that loss of iodine through profuse sweating may lead to iodine deficiency, and loss of electrolytes through sweating may have a dietary significance for heat-stressed individuals or for individuals.


Rule of water loss

1 kilogram of lost weight =  1 liter of fluid lost


Sweat iodine loss is estimated to be
Iodine loss 37µg = 1 liter water lost

 Average person sweats between
0.8 to 1.4 liters per hour
during exercise. (Hot Yoga will be greater)

Sauna  may loose 2 or 3 Liters

Hot Yoga Class = 1 - 3.5 liter

Possible ranges of iodine loss = 37µg  to 130µg 

If humidity is considered iodine loss may be considerably greater.

You may be loosing your RDA every class.


What if you are loosing 280µg to 350µg of Iodine per class.





The highest recorded sweat rate for an athlete in an exercise situation is 3.7 liters (125 oz.) per hour, recorded by Alberto Salazar while preparing for the 1984 Summer Olympics.

The highest human sweat rate recorded is 5 liters (169 oz.) per hour measured on a resting body exposed to a hot environment. At rest, the skin blood flow was maximum and not competing with exercising muscles.

An average person sweats between 0.8 to 1.4 liters per hour during exercise.


The Yoon Study

Dr Yoon from Korea noted that Hashimotos thyroiditis is reversible for some patients.


Japan has the highest dietary intake of iodine (13 mg per day), and the lowest rates for goiter and breast cancer

When Japanese women immigrate and change dietary intake of Iodine to the lower 150 mcg/day in America, breast cancer rates increase.

From Japan, Dr Funahashi reported a common seaweed food containing high iodine content is more beneficial than chemotherapy on breast cancer .




Recommendations for Hot Yoga Practitioners

The best ways to make sure you do not become iodine deficient is to eat sea vegetables a lot. Such as



More than 90% of ingested iodine is excreted in the urine within 24-48 hours such that daily iodine intakes in a population can be extrapolated from measures of median spot urinary iodine concentrations  according to WHO.

Urinary iodine is a well-accepted, cost-efficient and easily obtainable indicator for iodine status. Since the majority of iodine absorbed by the body is excreted in the urine.



Assessing iodine intake itself, measurement of urinary iodine concentration (UIC) or urinary iodine excretion per day (UIE) in a population is recommended as a reflection of recent iodine intake because “urinary iodine is well-accepted, cost-efficient and easily obtainable indicator for iodine status.

The effects of iodine deficiency on brain development are similar to those of hypothyroidism from any other cause. The United States, Canada, and most developed countries have routine screening of all very young children by blood spot for TSH or T4 to detect among iodine-sufficient children the approximately one in 4,000 who will be hypothyroid, usually from thyroid aplasia. Iodine treatment can reverse cretinism especially when the treatment is begun early (Klein et al., 1972)



Thyroglobulin, produced exclusively by the thyroid gland, has been proposed to be a more sensitive biomarker of iodine status than thyrotropin or the thyroid hormones triiodothyronine and thyroxine. However, evidence on the usefulness of thyroglobulin (Tg) to assess iodine status has not been extensively reviewed, particularly in pregnant women and adults.
Department of Human Nutrition, University of Otago , Dunedin, New Zealand.





The mean concentration of total iodine in drinking-water in the USA is 4 µg/litre, and the
maximum concentration is 18 µg/litre. This is presumably predominantly iodide.

According to WHO


Japan has the highest dietary intake of iodine (13 mg per day), and the lowest rates for goiter and breast cancer. When Japanese women immigrate and change dietary intake of Iodine to the lower 150 mcg/day in America, breast cancer rates increase.


Henan Provincial Institute for Health Inspection and Supervision, Zhengzhou

Study to investigate the amount of daily iodine intake in the diet of the target population in drinking water with areas of excessive iodine after stopping supply of iodized salt.


RESULTS: The median level of iodine in drinking water was 431.5 microg/L

It was concluded that drinking water was the main source of iodine intake in areas with iodine excessive water by the percentage of over 80%. It was necessary to adopt measures to improve the quality of water to decrease the iodine content other than just stopping supplies of iodized salt in the areas where the water iodine contents were greater than 300 microg/L, in order to prevent and control excessive intake of iodine.


Some studies have suggested over twice as much loss in our iodine content in humid environments.

Iodine intake of Japanese male university students: urinary iodine excretion of sedentary and physically active students and sweat iodine excretion during exercise. J Nutr Sci Vitaminol (Tokyo). 1985 Aug;31(4):409-15

Five males were shown to lose 2.3 times more iodine through sweat during an 8 hour period at 38.3oC (100.9oF) at 69% humidity than at 28.9oC (84.0oF) at 50% humidity.

A 1945 study Suzuki M, Tamura T.