Iodine Deficiency Linked to Increased Cancer Risk, Thyroid Disease - Dr Brownstein

Although it’s well established that iodine is necessary for thyroid hormone production, its therapeutic benefits extend far beyond that.

Iodine is present in every cell of our bodies and has antibacterial, antiviral, anti-parasitic, and anti-cancer properties and is required for proper immune function. It’s also vital for the normal architecture of essential glandular tissues such as the breasts, ovaries, uterus, pancreas, and prostate.

Testing for and treating iodine deficiency should, therefore, be a top priority to avoid serious complications, according to Dr. David Brownstein, a family physician and the medical director of the Center for Holistic Medicine in West Bloomfield, Michigan.

Related: Iodine vs Iodide, Deficiency, Supplementation and Iodine Rich Foods

Why We Need Adequate Iodine for Thyroid Health

“If you don’t have enough iodine, you can’t produce vital hormones the body needs, so having an iodine deficiency can lead to a diagnosis of hypothyroidism,” Dr. Brownstein said in a recent interview on Discovering True Health, a YouTube channel and podcast dedicated to health and wellness.

Iodine is essential for making thyroid hormones triiodothyronine and thyroxine, which are especially important in pregnancy and infancy for the proper development of a baby’s brain and bones.

The two hormones also help control body temperature, heart rate, and digestion and maintain healthy skin, hair, and nails.

Over time, hypothyroidism also increases the risks of heart disease, high cholesterol, and diabetes.

The thyroid requires a daily supply of iodine to manufacture sufficient hormones. It needs to capture about 60 micrograms of iodine from the bloodstream each day, according to a paper published in Sultan Qaboos University Medical Journal. If iodine levels are low, the thyroid enlarges to try to absorb more iodine. This compensatory swelling is called a goiter.

How Iodine Deficiency May Lead to Cancer

Studies on rats from decades ago revealed that iodine deficiency produced precancerous conditions, according to Dr. Brownstein. Iodine also has been found to have anti-cancer effects in laboratory studies using human cancer cells.

Iodine is thought to be one of the oldest antioxidants in living organisms, according to a 2021 review published in the Nutrients journal. One of iodine’s roles is scavenging reactive oxygen species. It interacts with and neutralizes these potentially damaging molecules, reducing their harmful effects on cells and tissues, thus reducing the risk of cancer.

Also, a 2017 review published in the Journals of Nutritional Health & Food Sciences found that “iodine deficiency is linked to ovarian cysts that hinder fertility and increase the risk of ovarian cancer. Iodine deficiency further can develop nodules and form fibrosis that can progress to cancer of thyroid, uterus, and breast cancer.”

“The reason we’re seeing such a rise in glandular cancer, including cancer of the breast, thyroid, and prostate, is … in part … this iodine deficiency that has taken hold of our country,” Dr. Brownstein said.

Breast Cancer

Breast cancer, currently affecting 1 in 8 women, will become the most prevalent cancer by 2040, according to recent estimates.

Iodine is necessary for the normal development of breast tissue and has been shown to suppress breast cancer cells and tumor growth.

“Studies dating back nearly 40 years ago show that iodine deficiency in rats produce the exact precancerous changes seen in humans—dysplasia and hyperplasia,” Dr. Brownstein wrote in his book “Iodine: Why You Need It, Why You Can’t Live Without It.”

study published in 1975 found that long-term iodine depletion led to atypical changes in rat mammary tissue. “This is the precursor to breast cancer,” Dr. Brownstein said.

It was also reported in a 1996 study published in the Journal of Surgical Oncology that after rats were induced with cancerous tumors using a carcinogen, iodine was shown to suppress tumor growth in breast tissue.

Breast tissue concentrates and stores iodine at high levels, according to Dr. Brownstein’s book, which supports the proposed link between iodine and cancer risk.

Two other factors contribute to the link between breast cancer and iodine deficiency, Dr. Brownstein wrote. First, iodine deficiency increases estrogen production, and second, it heightens the sensitivity of breast tissue to estrogen. Both outcomes “increase the chances of developing disease(s) of the breast, including breast cancer.”

A 2011 review article published in the Journal of Evidence-Based Integrative Medicine also notes a significant connection between breast cancer and thyroid disease, indicating a potential shared factor, with iodine deficiency possibly being the common link.

Prostate Cancer

There is limited research on the role of iodine in prostate cancer, the second-leading cause of cancer death in men in the United States.

2007 study investigated the possible link between iodine deficiency and the risk of developing prostate cancer. The findings revealed that people with the highest urinary iodine to creatinine ratios had a 29 percent lower risk of developing prostate cancer than those with the lowest iodine levels.

Additionally, a history of thyroid disease doubled prostate cancer risk, with those having had thyroid disease for more than 10 years having more than three times the risk.

“Although the role of dietary iodine remains speculative, a role for thyroid disease and/or factors contributing to thyroid disease as a risk factor for prostate carcinogenesis warrants additional investigation,” the study authors wrote.

Other Common Cancers

The thyroid gland heavily relies on iodine, and iodine deficiency has long been recognized as a factor associated with a higher risk of developing thyroid cancer, the most common malignancy of the endocrine system.

Because of its effect on the endocrine system, low iodine intake has been associated with an altered hormonal state. A study published in The Lancet highlights the potential link between low iodine intake and increased risk of breast, endometrial, and ovarian cancers, suggesting that increasing dietary iodine intake may help reduce the risk of these cancers.

Rates of uterine and ovarian cancer are currently on the rise, with uterine cancer becoming more prevalent in women under 49.

Why Is Iodine Deficiency Surging?

Officially, iodine deficiency affects an estimated 35 to 45 percent of the global population. But the actual number may be much higher, according to Dr. Brownstein, who has more than 25 years of experience testing thousands of people. Most people aren’t routinely screened for this essential nutrient, he said.

Several factors cause iodine deficiency.


One significant contributing factor to iodine deficiency is the depletion of iodine in the soil, according to Dr. Brownstein. “We used to get iodine from some of our food grown in iodine-containing soil,” he said. But overfarming and the use of pesticides and insecticides containing toxins such as fluorine and bromine have led to its reduction.

Ocean Pollution

The oceans, another significant source of iodine, have been polluted, which has further contributed to the problem, Dr. Brownstein said. Man-made chemical pollutants such as plastics and heavy metals not only harm marine life but also contaminate seafood, a known source of dietary iodine.

That means that the iodine we could get from these natural sources now comes with other substances we would be better off without.

For example, seaweed and seafood are excellent sources of dietary iodine, but studies have found high levels of heavy metals such as lead, cadmium, and arsenic in both.

Overexposure to Halides

The balance between essential and nonessential halides, chemical compounds containing halogens, plays a role in iodine deficiency. According to Dr. Brownstein, excessive bromide or fluoride can displace iodine in the body.

2020 study published in Nutrients outlines how bromine and brominated compounds, as well as fluoride and fluorinated compounds, have been found to interfere with iodine uptake.

Bromine is used as an insecticide, fumigant, water purifier, emulsifier in soft drinks, and dough softener and is found in fire extinguishers, pharmaceuticals, and bromated vegetable oil. It’s also a fire-proofing agent in mattresses, curtains, carpets, furniture, and clothing.

Fluoride isn’t only added to the water supply in the United States but is also found in our air, soil, food, drinks, medications, and dental products.

Assessing Iodine Status

Iodine deficiency can lead to hypothyroidism and other thyroid issues, as inadequate iodine prevents the thyroid from producing sufficient hormones, affecting people in a multitude of ways, some of which may not be obvious.


Some symptoms of iodine deficiency are:

  • Fatigue: You may feel tired and sluggish, even after getting enough sleep.
  • Menstrual irregularities: Women may experience heavy or irregular periods and infertility in more extreme cases.
  • Weight gain: You may have unexplained weight gain or difficulty losing weight despite proper diet and exercise.
  • Cold sensitivity: You may feel excessively sensitive to cold temperatures.
  • Dry skin and hair, and brittle nails: Your skin may become dry, rough, and flaky, and your hair may become brittle and thin.
  • Muscle problems: You may experience muscle weakness, cramps, or aches.
  • Constipation: Slower digestive processes can lead to constipation.
  • Mood swings: Changes in hormone levels can affect mood and lead to feelings of depression, irritability, or mood swings.
  • Memory problems: You may experience forgetfulness, difficulty concentrating, and mental fog.
  • Swelling in the neck: You may notice throat pain, difficulty swallowing, or hoarseness.


The iodine loading test, developed by Dr. Guy Abraham, is considered one of the best functional tests for evaluating iodine status, according to Dr. Brownstein. The test measures iodine content in the urine before and after taking an iodine supplement.

“By subtracting these numbers, you can determine how much iodine your body retained,” he said. “Because iodine is cleared mostly through the kidneys, the amount retained reflects the body’s deficiency level.”

If only a small portion is retained and most is excreted, it indicates the body has sufficient iodine stores. High retention and low secretion signal iodine deficiency, as the body holds onto more of the supplemental iodine to replenish depleted levels.

Most people tolerate iodine supplements well, but some may have sensitivities, Dr. Brownstein said. Possible reactions include headaches and upset stomach.

“It is always advisable to seek the guidance of a knowledgeable health care professional who is familiar with iodine supplementation and testing,” he said.


The recommended dietary allowance for iodine is 150 micrograms. This is the minimum daily amount estimated to prevent developing a goiter, based on animal studies, according to Dr. Brownstein. “But this is not the optimal amount,” he said.

Research published in the Sultan Qaboos University Medical Journal found that the body of a healthy adult contains 15 to 20 milligrams of iodine. About 70 to 80 percent of that is used by the thyroid gland.

Given differences in factors such as exposure to iodine-displacing chemicals, optimal daily iodine intake can vary significantly among individuals. Optimal intake is best determined through lab testing and guidance from an iodine-knowledgeable practitioner, Dr. Brownstein said.

Our bodies store some nutrients but lack reserves of accumulated iodine. “If you don’t take iodine for a day or two, you start to become deficient,” he said.

It’s best to obtain nutrients from food, particularly from an organic diet, as it generally contains lower amounts of pesticides and insecticides, which reduce iodine uptake.

Specific diets, such as the following, may cause iodine deficiency:

  • Diets without ocean fish or sea vegetables
  • Diets containing low-iodized salt
  • Vegan and vegetarian diets
  • Diets high in consumption of bakery products that contain bromide

But Dr. Brownstein said: “It’s impossible in our toxic world to get enough iodine from food; you just can’t. I believe most people will need to supplement it.”

Lugol’s Solution

Different tissues in the body require varying forms of iodine; some preferentially take up iodide, the reduced form, which contains an extra electron, and others prefer iodine, the oxidized form, according to Dr. Brownstein.

“A combination of iodine and iodide, such as Lugol’s iodine solution [5 percent iodine (I2) and 10 percent potassium iodide (KI)], can effectively target the iodine-requiring receptors in the body,” he said.

Dr. Brownstein said that he could reduce thyroid hormone dosages significantly when he started using Lugol’s solution before thyroid hormone treatment.

“The percentage of my patients requiring thyroid hormone decreased from 75 percent to 25 percent, and the average dose decreased from two grains (120 milligrams) to 30 milligrams of natural thyroid hormone,” he said. “Additionally, about 50 percent of these patients were able to discontinue thyroid hormone treatment altogether, as I addressed the underlying cause of their hypothyroidism, which was iodine deficiency.”

When Taking Iodine, Don’t Forget the Salt

When Dr. Brownstein’s patients began using iodine supplementation, those with low salt intake reported experiencing adverse reactions, he said. In those cases, the patients unintentionally triggered the release of bromide and, in some cases, fluoride from tissues.

This detoxification process can lead to fatigue or headaches, he said. “I find that taking salt with iodine really minimizes the side effects. Enough salt will competitively inhibit bromide and help its excretion.”

But not all salt is created equal. “There is good salt and bad salt,” Dr. Brownstein said. Refined salt, the thin white salt you usually see in restaurants, should be avoided, he wrote in his book “Salt Your Way to Health.”

Refined table salts are stripped of minerals and often contain additives such as anti-caking agents, ferricyanide, and aluminum. Unrefined crystal salts such as Celtic sea salt, Redmond Real Salt, and Himalayan salt provide chloride and more trace minerals.

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