An Investigation: Iodine & Hair Health
Iodine is a mineral featured in many top-selling hair loss supplements. The rationale for its inclusion? That iodine is an essential nutrient for thyroid function. And, since thyroid disorders are linked to hair loss, iodine must also be critical for hair growth.
There is some truth to this claim. At the same time, this truth is all context specific.
For instance, many people don’t know that iodine supplements are only appropriate for a small percentage of hair loss sufferers. Moreover, there are cases where iodine supplementation may actually cause hair loss.
To understand why, we’ll need to uncover:
- The science behind iodine: what it is, its effects on the thyroid, and its role in hair loss and hair growth.
- The percent of hair loss sufferers who are iodine deficient.
- The scenarios in which iodine will help or hurt or hair.
This article unpacks the evidence, the answers, and more.
What is iodine?
Iodine is an essential mineral found in fish, kelp, dairy products, and (in many countries) salt. It plays crucial roles in the maintenance of brain, thyroid, and metabolic health. It’s especially important for the growth and development of fetuses and children.
Iodine: an essential trace element
In 1990, almost one-third of the global population was affected by iodine deficiency, making it the single greatest preventable cause of brain damage. As such, salt iodization programs were initiated at the national level, leading to a drastic decline in the incidence of iodine deficiency. Today, only 8.8% of people in the U.S. are considered iodine deficient.
So, who are these individuals who are iodine deficient or at risk of a deficiency? And are these deficiencies linked to hair loss?
To answer these questions, we’ll first unpack the evidence on iodine and hair loss. Then, we’ll establish when iodine deficiencies are connected to hair loss (and when they aren’t).
Finally, we’ll reveal evidence for why people should think twice about taking iodine for hair health. After all, there’s evidence that iodine supplementation can hurt our thyroid, too… and maybe even our hair.
Is there any evidence that iodine plays a role in hair growth or hair loss?
Yes. Evidence from human and animal studies suggests that iodine deficiencies may contribute to hair health, and in a few ways:
- Thyroid hormones are essential for maintaining the growth of hair. This is why hypothyroidism, a state of low thyroid hormone, is directly connected to hair loss. Iodine is essential for the creation of thyroid hormones and, thus, deficiency may limit thyroid hormone synthesis. Hypothyroidism is mostly linked to telogen effluvium, a hair shedding disorder that leads to non-permanent diffuse hair loss. But it has also been linked to female androgenic alopecia (AGA).
- Thyroid hormones have been shown to reduce skin fibrosis in animal studies. Thyroid hormones may, therefore, limit (but not necessarily fully block) fibrosis that contributes to follicle miniaturization in AGA.
So, iodine might affect hair growth… primarily due to its role in thyroid hormone production. To recap: without enough iodine, the thyroid can’t function properly, which can lead to hypothyroidism (an under-active thyroid). And when hypothyroidism is severe enough, hair loss can occur… specifically in the form of telogen effluvium and/or (maybe) female pattern hair loss.
So, can an iodine deficiency cause hair loss?
It’s possible. After all, iodine deficiencies can lead to hypothyroidism, and hypothyroidism can lead to telogen effluvium and/or exacerbate female pattern hair loss.
But just because iodine deficiencies may cause hair loss in certain scenarios does not mean you should supplement with iodine. Why? Because the scenarios we’ve outlined above are relatively uncommon… especially in the developed world.
Consider the following:
- Only 8.8% of Americans are deficient in iodine.
- Only 3-15% of adults in America or the U.K. have subclinical hypothyroidism (source).
Moreover, hypothyroidism can stem from many different causes – i.e., autoimmune disorders, chronic conditions, nutrient deficiencies from zinc and iodine, and more.
That means that only a fraction of the 3-15% of adults with hypothyroidism have hypothyroidism due to an iodine deficiency.
In other words, the percentage of American adults who might benefit from iodine supplementation is 8.8%… and the percentage of American or U.K. adults who might see hair regrowth from iodine supplements is much less than 8.8%.
This means that iodine supplementation is unlikely to help the majority of hair loss sufferers in the developed world. In fact, there are even scenarios where supplementing with iodine might be dangerous, or maybe even cause hair loss.
Here’s how.
Iodine helps the thyroid but, paradoxically, may induce hypothyroidism
Following the iodization of salts, the U.S. and other countries began to see a decrease in the prevalence of goiters – large growths on the neck which are often indicative of hypothyroidism. This, along with the evidence of decreased (preventable) brain damage all pointed to the fact that widespread iodization was working; it was preventing preventable diseases and making people healthier. Moreover, for most people, it seemed like the increased iodine consumption was generally well tolerated. These are all positives.
However, there’s always two sides to every story.
For instance, this meta-analysis of 50 studies revealed that yes, iodization (i.e., widespread iodine supplementation through salts) did decrease the number of goiters. But interestingly, chronic exposure of iodine also increased the incidence of hypothyroidism – mostly in places that were otherwise getting enough iodine to begin with.
This implies that iodine’s effects on thyroid health is biphasic. In other words, both low iodine and high iodine intake can lead to hypothyroidism. Therefore, we shouldn’t shoot to consume as much as possible; we should shoot to consume the optimal amount daily (more on this later).
Iodine helps the thyroid but, paradoxically, may induce hyperthyroidism
Hyperthyroidism is the opposite of hypothroidism; it’s when the thyroid is over-active. And interestingly, hyperthyroidism (like hypothyroidism) is also linked to hair loss, but through a different set of mechanisms.
Whereas hypothyroidism may evoke hair shedding as a result of “metabolic conservation”, hyperthyroidism exposes our hair follicles to too much thyroid hormone – which may deplete hair follicle stem cells (i.e., cells that are necessary for hair growth).
Interestingly, hyperthyroidism is also (paradoxically) sometimes linked to excess iodine intake.
This phenomenon was first observed after the implementation of universal iodization programs. Researchers found that the incidence of hyperthyroidism began to increase in various countries. In some cases, these increases occurred directly alongside increases in salt iodization, suggesting a direct relationship.
Some evidence suggests that hyperthyroidism from excess iodine may also be due to too large of a jump in iodine intake, too quickly. In other words, it seems more prevalent in those jumping from extremely low iodine intake to extremely high iodine intake – which is really only possible through supplementation.
As such, it’s best to fully understand your iodine needs – and your own intake – before considering supplementing.
Any other health concerns with iodine supplementation?
Yes, primarily thyroid cancer.
Studies on populations in Iceland, Hawaii, and China have indicated that increased iodine intake may be a factor in some forms of thyroid cancer. At the same time, the body of research suggests yet another biphasic effect of iodine: low levels of iodine are also a risk factor for thyroid cancers.
So, it appears that both high and low intakes of iodine are implicated in cancer. Again, all roads lead to optimal iodine intake… not deficiencies or excesses.
How severe would an iodine deficiency need to be to cause hair loss?
For hypothyroidism to occur and thereby lead to telogen effluvium-related hair loss, one would have to consume less than 10-20 mcg of iodine per day. This is less than 15% of the recommended daily intake for adults.
For reference, just a quarter teaspoon of iodized salt contains 71 mcg – a quantity high enough to prevent iodine deficiency-related hypothyroidism. But, even for those who don’t consume iodized salt, one egg alone contains 24 mcg. And in most cases, one egg daily would be sufficient to prevent hypothyroidism, and thereby hypothyroid-related hair shedding.
Thus, most cases of hypothyroidism-induced hair loss are likely not attributed to iodine deficiency..
What might interfere with the thyroid’s ability to use iodine?
Beyond iodine consumption, there are some additional factors that can influence the thyroid’s ability to utilize iodine:
- Fluoride. Fluoride has been shown to impair iodine transport and absorption, which impairs thyroidal access to iodine.
- Goitrogens. Goitrogens are compounds found in cruciferous vegetables, legumes, cabbage, kale, cauliflower, broccoli, turnips, and canola. These compounds compete for iodine uptake in the thyroid, thereby displacing active iodine for thyroid hormone synthesis.
But, how likely is it that our fluoride and goitrogen exposure actually influences hypothyroidism?
Some animal studies indicate that goitrogen consumption may impair thyroid function even in the presence of adequate iodine consumption. However, the general consensus is that goitrogens in normal quantities are unlikely to induce hypothyroidism in the presence of optimal iodine intake.
In regards to fluoride, it only appears to be an issue in the case of moderate to severe iodine deficiency. So, again, the risk profiles here are all relative… and relatively small.
How can we safely maintain iodine levels?
A balanced diet with plenty of high-quality plant and animal foods is more than likely to provide all the iodine you need for sufficiency.
However, if you’re concerned that maybe your diet is slightly devoid of iodine, here are some foods you may consider adding to your diet:
|
Foods and their respective iodine content |
|
| Iodized salt (¼ tsp) | 71 mcg (47% DV) |
| Seaweed (1g) | 16-2,984 mcg (11%-1,989% DV) |
| Cod (3 oz) | 99 mcg (66% DV) |
| Low-fat yogurt (1 cup) | 75 mcg (50% DV) |
| Reduced fat milk (1 cup) | 56 mcg (37% DV) |
| Eggs (1 egg) | 24 mcg (16% DV) |
Beyond that, avoiding iodine in your supplements is probably a good idea.
Iodine is readily accessible and abundant in foods – at least foods available in the developed world. Therefore, supplementation isn’t going to confer many benefits, as only 8.8% of people even have a gap to fill (which can be filled by changing your diet).
Moreover, since iodine supplementation increases the risk of excess intake, this might elevate our risk of thyroid-related problems and, by association, our hair loss. Therefore, iodine supplementation runs the risk of sabotaging our efforts to regrow hair.
In light of this evidence, we’ve never understood why so many hair loss companies are hellbent on including iodine in their supplement line.
For peace of mind, you may also want to reduce your exposure to goitrogens and fluoride by (1) cooking your cruciferous vegetables and (2) filtering your drinking water with a fluoride-removing filter. This should dramatically reduce your exposure to compounds that can interfere with iodine bioavailability.
Aside from that, the evidence suggests that iodine is worth getting from food sources and iodized salt rather than a hair loss supplement. So, if you see a supplement with iodine, and you don’t have hypothyroid-related hair loss due to an iodine deficiency… maybe keep shopping.
Summary
Iodine is essential trace element. It helps support kidney, skin, brain, and thyroid health – and it’s also to help produce thyroid hormones.
Iodization programs have drastically reduced the incidence of iodine deficiencies globally. According to the latest estimates, only 8.8% of Americans have an iodine deficiency. And since both an iodine deficiency as well as iodine excess can cause thyroid-related problems, most Americans (and others in developed countries) should be avoiding iodine supplements.
Moreover, the only scenarios where iodine deficiencies are linked to hair loss seem to occur when someone develops hypothyroidism as a result of an iodine deficiency. While subclinical hypothyroidism affects 3-15% of people in the developed world, the percent of people dealing with hypothyroidism from an iodine deficiency is only a fraction of that percent. Therefore, very few people with hair loss would benefit from an iodine supplement – if at all.
Moreover, iodine excess is associated with both hyperthyroidism and thyroid cancer. For these reasons, iodine supplementation is not only unnecessary for most hair loss sufferers, but it’s also potentially dangerous.
The bottom line? Aim to get most of your iodine from food, and avoid supplements that contain iodine. If you’re concerned of a deficiency, consider increasing your seaweed intake, reducing your exposure to goitrogens, and filtering your drinking water to remove the fluoride. This will help to ensure your iodine levels remain in that narrow therapeutic window — the middle ground that promotes health and supports hair growth.
Rob English is a researcher, medical editor, and the founder of perfecthairhealth.com. He acts as a peer reviewer for scholarly journals and has published five peer-reviewed papers on androgenic alopecia. He writes regularly about the science behind hair loss (and hair growth). Feel free to browse his long-form articles and publications throughout this site.
Hi Rob, long-time nutrition researcher here (Master in Nutritional Epidemiology from the Harvard School of Public Health). I also have subclinical hypothyroidism, so I have been doing personal research the topic of thyroid health (including iodine) for many years. Iodine is unfortunately a much more complex topic than this article suggests, and a lot of evidence suggests that the RDA for iodine is much too low, especially for women, who need extra iodine for breast health and reproductive health — which suggests that it is not a coincidence that women are much more likely to suffer from hypothyroidism compared to men. Furthermore, many people nowadays use iodine-free salt, and many others are on low-sodium diets, and/or consume food grown in iodine-deficient soils. So your suggestion to avoid iodine in supplements is a bit misleading (and potentially dangerous, especially in the case of women).
Most medical professionals are unfortunately under-educated on the topic of iodine, especially given its complexity. Judging from your article, it would seem that you may not have read materials written by iodine-literate doctors. I would suggest starting with Dr. Brownstein’s book: “Iodine: Why You Need It, Why You Can’t Live Without It”. Here is a preview: optimox/com/iodine-study-9
Hey Cristina,
Thanks for reaching out, and for passing along a link to Dr. Brownstein’s website.
I’m always open to revising my opinions – especially in light of new evidence (or evidence to which I was previously not aware). Having said that, I don’t think Dr. Brownstein should be anyone’s go-to resource for iodine.
Here are just a few of the issues I found with Brownstein’s article – specifically his claims and the way he presents information:
1. Brownstein states that he tests his patients for an iodine deficiency using urinary iodine loading tests. According to the article, his source of inspiration for this test this came from reading a doctor newsletter: “Townsend Letter for Doctors and Patients titled ‘Iodine Supplementation Markedly Increases Urinary Excretion of Fluoride and Bromide'”. Iodine loading tests involve having patients supplement with ~50mg/daily of iodine, then measuring urinary clearance of iodine over a 24-hour period. If 90% of that iodine is cleared via the urine during this window, someone is considered iodine replete. If less is cleared, then according to Dr. Brownstein, that person is considered iodine deficient – because much of the uncleared iodine must’ve been taken up by the body. Using this testing methodology, Brownstein cites that 94.7% of the 500+ patients he has tested are iodine deficient. Thus, he implies that iodine deficiency is far more widespread than commonly believed.
Unfortunately, Brownstein doesn’t comment at all about the unreliability of urinary iodine load testing. Ironically, the very publication that inspired Brownstein to begin iodine load testing (Townsend Letters) later published a study demonstrating just how diagnostically useless an iodine load testing actually is. You can read that here. To quote from the text’s discussion:
These data were partly what inspired David Zava, PhD (who focuses on breast cancer research) to write, “Flaws in the Urine Iodine Loading TestCan Lead to High Dose Iodine Therapy and Disrupted Thyroid Function“, where he states that the popularity of iodine load testing arose mostly from “a false premise based on a miscalculation of how much iodine the Japanese consume on a daily basis, which was thought to average 13.8 mg/day1, mostly in the
form of seaweeds known to be high in iodine. However, a more thorough analysis of the literature finds that the Japanese daily consumption is in fact much lower than this, ranging between 1 and 3 mg/day2”.
So, Brownstein is building his argument for widespread iodine deficiency by using a flawed iodine deficiency test – one that generally produces an iodine-deficient result in 90%+ of the people who take it, regardless of their health or iodine status. To me, this isn’t evidence of a widespread deficiency; it’s evidence of an unreliable testing methodology.
2. Brownstein cites an 8-person study as evidence that high-dose daily iodine supplementation can help to “saturate [the body] with iodine while at the same time detoxifying from the toxic halides bromide and fluoride.” This statement is confusing, and for many reasons.
For starters, bromine has recently been recognized as an essential element. I’m all for believing that bromine can be toxic in high dosages (as most things are), but I’m not sure why Brownstein is referring to this element as toxic from the get-go, and as if its detoxification from the body is a good thing (as doing so implies that bromine/bromide is problematic at any dose).
Secondly, Japanese seaweed – which is high in iodine – also contains ~10x more bromine than iodine. Brownstein has argued that one reason why Japanese populations are so robust / healthy is because of their seaweed (and thereby, iodine) intake. How can he hold this belief if he also believes that mega-dosing iodine helps to clear out “toxic” bromine? This seems a bit contradictory.
Thirdly, there’s also evidence that iodine supplementation does not clear out bromide/bromide, and that the effects of the 8-person study cited by Brownstein were likely the result of using Ion Electrode testing rather than more advanced testing methodologies. To quote from this author:
3. Brownstein claims that, “Iodine levels have fallen over 50% in the last 30 years in the United States”. His source for this claim is The National Health and Nutrition Survey. This is self-reported survey data; it’s a survey that asks for participants to recall their food choices. It’s not serum or urinary iodine readings. So, Brownstein’s claim misconstrues the data he’s using to support his statement. In fact, his claim is just outright wrong… because we can’t use self-reported food data as a surrogate for someone’s actual nutritional statuses.
On that note, Brownstein neglects to mention that 1/3rd of the participants in recent NHN surveys actually provided urine samples for iodine, and that this data was also published (source). The conclusions from the authors?
4. Brownstein’s article relies almost entirely on his clinical experience mega-dosing patients with iodine. It relies on very little peer-reviewed publications, and of the publications he does cite, he seems to have either cherrypicked those studies, misrepresented their findings in the context of the broader researcher, or made false claims about the actual data he uses to build his case (see points #1-#3).
5. Brownstein sells iodine supplements. I wouldn’t necessarily see this as a problem, but given all of the issues above, this has to be biasing his interpretation of the evidence.
I’m not saying that mega-dosing iodine is problematic for everyone. In some cases, it might be great! And I do think iodine supplementation makes sense for many people – especially those with iodine deficiency-driven hypothyroidism. And in those cases, there’s a chance that iodine supplementation may even help improve hair loss.
Having said that, I think that Dr. Brownstein is a far cry from an “iodine-literate doctor”. His unreliable testing methodologies, cherrypicked studies, paradoxical viewpoints, mischaracterizations of survey data, and near-complete absence of citations paint him more like an unreliable narrator than a medical professional. But I’m happy to hear your thoughts on the above. Again, I’m always open to revising my opinions.
All my best,
Rob
Hey Rob,
Thanks for the comments!
Dr. Brownstein aside — let’s assume that he is wrong on almost everything he says about iodine — we do know that the body (not just the thyroid) needs iodine. And we can reasonably assume that some people do not get the RDA from their usual diet, given that in many places of the world the soil is low in iodine, and some people do not consume iodized salt or iodine-rich foods. (And that is under the conservative assumption that the RDA is actually the optimal amount of iodine we need, because we know that the RDA for many nutrients only represents the bare minimum required to prevent overt deficiency/acute symptoms of deficiency — e.g. rickets from vit. D deficiency or scurvy from vit. C deficiency, or, in the case of iodine, goiter).
Iodized salt was introduced to prevent goiter, but many people nowadays use non-iodized salt, and do not eat iodine-rich foods such as sea plants. We also know that supplementation of the RDA amount of iodine (150 mcg) is very safe and unlikely to cause problems, even in people at risk of thyroid issues, but that it can have significant benefits for those who are deficient (and may not know it) or at risk of deficiency.
NHANES did show a significant decrease in iodine status as measured from urine, and that the 1988-1994 population group had a 4.5-times increase in deficiency compared to the 1971-1974 population: “the median concentration decreased more than 50% between 1971-1974 (32.0+/-0.6 microg/dL) and 1988-1994 (14.5+/-0.3 microg/dL). “Low UI concentrations (<5 microg/dL) were found in 11.7% of the 1988-1994 population, a 4.5-fold increase over the proportion in the 1971-1974 population." (https://pubmed.ncbi.nlm.nih.gov/9768638/)
So, again, I think that advising against taking even small amount of iodine (1 mg per day or less) is dangerous advice, especially in the case of women, who need iodine for breast and reproductive health (not to mention during pregnancy).
Iodine is essential for breast health (https://pubmed.ncbi.nlm.nih.gov/16025225) and has been found to help women who have fibrocystic breast disease: "A review of clinical studies found that iodine replacement therapy (particularly for those with low levels of iodine) may improve the tenderness associated with fibrocystic breast tissue." (Mount Sinai: https://www.mountsinai.org/health-library/supplement/iodine; Ghent WR, Eskin BA, Low DA, Hill LP. Iodine replacement in fibrocystic disease of the breast. Can J Surg. Oct 1993;36:453-460.)
Iodine deficiency is also suspected to be linked with the increased incidence of breast cancer in younger women (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5327366/).
Given the low risk and high potential benefits of low-dose iodine supplementation (in people at risk of deficiency or who are deficient without knowing it, and especially for women), I do think you should revise your recommendation against taking low-dose iodine. You advise people to get most of their iodine from food, but soil levels of iodine vary greatly, thus making the iodine content of foods unreliable (not to mention that we often do not know where our food was grown) — so for most people it is impossible to be certain we are consuming enough iodine, unless they consume sea plants (and we know that some sea plants can contain heavy metals, so a careful selection is needed) or consume enough iodized salt (which people on low-salt diets can't).
So, the only solution to prevent deficiency is to take a (low-dose) iodine supplement. Many multivitamins do include the RDA for iodine (150 mcg), but for people who do not take multivitamins, an iodine supplement — at the very least once or twice a week — provides an insurance against iodine deficiency with minimal risk.
I can only speak for myself regarding iodine and I am not knowledgeable on the topic.
I do believe that iodine is misunderstood on all sides though.
That said, I discovered iodine by accident so here’s a brief run-down on my experience with it.
I’m in my mid 40s and started having trouble taking a pee and two years ago I had a mini stroke and at that time all I knew about iodine was that it was poison and that Bart Simpson said it stings haha.
Anyway, I had to have an iodine injection to show up any problem blood vessels in an mri scan after my stroke.
I was afraid but felt that the risks taking iodine were worth it.
I signed a disclamer about the what iodine could possibly do to make me sick.
Any way, I had the injection.
I didn’t notice any health side effects.
But two weeks later I noticed I was peeing like a champion. So what could only have been attributed to an enlarged prostate was set straight by his mega dose of iodine.
I started reading about iodine and the prostate and it turns out that many people use it successfully for prostate issues.
I also have dandruff and so I thought, let’s see what iodine does on my scalp.
Well, within two days my dandruff was gone AND my scalp felt way less inflamed.
I have started taking it regularly in the morning and within about 15 mins, I feel energised like I’ve had a coffee but without the come down.
So I can’t say that iodine is good or bad but I couldn’t be without it.
My experience has been completely unintentional, completely personal and totally unbiased by internet quacks that peddle iodine.
Thanks for sharing very useful information, bro!
Do a research on hardwater.
Distilled water is best for hair wash. Try it!
* Meant to type “goiter” not gout in the comment I submitted a few minutes ago 🙂 Can’t edit it.
Hi Rob,
I missed a test in your article, by which we can define our levels of iodine.
Iodine patch test: The iodine patch test is a test where doctors paint a patch of iodine on your skin and check how it looks 24 hours later. For those who are not iodine deficient, the patch fades no sooner than 24 hours. But a deficiency will likely cause the iodine to be absorbed into the skin more quickly.
Best regards,
Vincenzo