Iodine: deficiency or excess, what is the real danger in France?

We have been working in the world of algae for over 12 years, and I have personally been consuming them for 25 years. If there is one topic that constantly comes up in our customers' questions, it is iodine. And honestly, I understand: between those who tell you that you are severely lacking it and those who warn you about the dangers of excess, it's easy to get confused.

So I wanted to lay things out clearly in this article. No alarmist rhetoric, no excessive simplification. Just the facts, the scientific data, and our feedback after almost two decades of helping people in their discovery of the Seaweed, superfoods of the sea.

And I tell you right away: what I discovered while compiling the data for this article has reinforced a strong conviction in me. In France, the real problem, the one that silently affects millions of people, is not an excess of iodine. It's the deficiency.

Why is iodine so important for your health ?

Iodine is an essential trace element that your thyroid gland critically needs to produce the hormones T3 and T4, which regulate the metabolism of nearly every cell in your body. An insufficient intake leads to fatigue, weight gain, and cognitive disorders.

The fundamental role of iodine in the thyroid

Imagine a tiny conductor, located at the base of your neck, constantly coordinating your metabolism, energy, body temperature, mood, and heart rate. This conductor is your thyroid. And its essential fuel, without which it simply cannot function, is iodine.

Specifically, your thyroid captures the iodine circulating in your blood to produce two fundamental hormones: T3 (triiodothyronine) and T4 (thyroxine). These hormones regulate the functioning of practically every cell in your body. Without iodine, there is no T3 or T4. Without T3 or T4, your entire metabolism slows down.

The principle is simple: your thyroid is like an engine. Iodine is the fuel. You can have the best engine in the world, but if it doesn't have fuel, it won't start. To better understand the role of these trace elements, essential catalysts for your health, I invite you to consult our dedicated file.

Beyond the thyroid: the lesser-known functions of iodine

What many people don't know is that iodine is not only used for the thyroid. In fact, this trace element is involved in much broader functions than what we are generally taught.

Iodine plays a role in brain development, and it is particularly critical during pregnancy and early childhood. A study published in The Lancet In 2013 (ALSPAC cohort), it was shown that even a mild iodine deficiency in pregnant women could have a measurable impact on the cognitive development of the child (1). We are not talking about severe deficiencies in developing countries, but about European women with simply insufficient intake.

Iodine also contributes to the normal functioning of the nervous system, the maintenance of healthy skin, and supports normal cognitive functions. It is a trace element with modest quantity requirements (150 µg per day for an adult), but its absence causes considerable damage.

Iodine deficiency in France: an underestimated problem

According to data from the INCA survey conducted by ANSES, 43% of women of childbearing age in France have insufficient iodine intake. This figure positions iodine deficiency as a major public health issue, far ahead of the risk of dietary excess.

43% of French women are deficient: ANSES data

Here is a figure that should give pause for thought: according to data from the INCA survey conducted by ANSES, 43% of women of childbearing age in France have insufficient iodine intake. Forty-three percent. Almost one in two women.

And this is not an isolated phenomenon. The World Health Organization (WHO) published a report in 2024 warning about the return of iodine deficiency in Europe, including in countries that were thought to be spared thanks to iodized salt programs.

Frankly, when I discovered these figures a few years ago, it caught my attention. We are in a developed country, with access to a diverse diet, and yet we are facing a massive deficit in an essential trace element. How did we get here ?

Several factors explain this situation. First, the gradual reduction in salt consumption (recommended for cardiovascular health, of course) has mechanically reduced iodine intake through iodized salt. Additionally, French soils are naturally low in iodine, which limits intake through vegetables and cereals. Furthermore, dairy products, which were historically a source of iodine due to iodine solutions used to disinfect milking equipment, have seen their iodine content decrease with changes in hygiene practices.

In summary: iodine sources are drying up, and we are not compensating. To delve deeper into the topic, find our analysis in the article. scientific studies on algae and the thyroid.

Iodine deficiency and normal TSH: the overlooked paradox

Here is something that very few people know, including some healthcare professionals. You can be iodine deficient while having a perfectly normal TSH.

TSH (thyroid-stimulating hormone) is the hormone that your doctor measures first to assess thyroid function. If it is within the normal range, you are generally told that "everything is fine." However, TSH can remain normal for a while even as your iodine reserves gradually deplete. Your thyroid compensates, it adapts, it makes do with what it has. Until the day it can no longer.

It's a bit like a bank account: you can continue to live normally as long as there is money left, even if your balance decreases each month. The day the account hits zero, it's a crisis. It's the same with iodine.

To truly assess your iodine status, it would be necessary to measure ioduria (iodine concentration in urine over 24 hours). However, this test is rarely prescribed routinely. As a result, thousands of people live with a subclinical deficiency that silently erodes their energy, concentration, and overall well-being. To better understand how diet plays a key role here, consult our report on Hypothyroidism and the role of iodine in seaweed.

Symptoms of iodine deficiency not to ignore

Do you feel tired for no apparent reason? Do you feel like your brain is running slow, especially at the end of the day? Are you gaining weight even though your diet hasn't changed? Is your skin dry, your hair brittle? Do you feel cold when everyone around you is comfortable ?

You might attribute these symptoms to stress, lack of sleep, or age. However, they could be signs of an iodine deficiency affecting your thyroid function.

Here are the main symptoms to know:

• Persistent and unexplained fatigue : it is often the first sign, the one that is most trivialized
• Weight gain despite a balanced diet : the metabolism slows down when the thyroid lacks iodine
• Excessive chilliness : the thyroid also regulates thermogenesis
• Concentration and memory disorders : the famous "brain fog"
• Dry skin, fine and brittle hair : cell renewal is slowed down
• Constipation : intestinal transit also depends on thyroid hormones
• Depressive mood, irritability : thyroid hormones directly influence brain chemistry
• Swelling in the neck (goiter) : in advanced cases, the thyroid enlarges in an attempt to absorb more iodine
• Irregular menstrual cycles : in women, the thyroid influences the hormonal cycle
• Decrease in libido : consequence of general fatigue and hormonal imbalance

Obviously, these symptoms can have other causes. But if you experience several of them, it would be wise to discuss it with your doctor and request a complete thyroid assessment, ideally including an ioduria test.

Excess iodine: a real risk but often overestimated

According to French nutrivigilance data, only 4 cases of adverse effects related to excess iodine from food sources have been documented in France. The vast majority of excess cases are linked to overdosed dietary supplements or medications, not to food.

The Wolff-Chaikoff effect: when too much iodine blocks the thyroid

Let's now talk about the other side of the balance, because I want to be completely transparent. Yes, an excess of iodine can be problematic. It's a scientific fact that should not be minimized.

The main mechanism is called the Wolff-Chaikoff effect. When the thyroid suddenly receives a very large amount of iodine, it temporarily goes into "block" mode. It stops producing hormones, somewhat like a fuse blowing to protect an electrical installation. In most healthy individuals, this blockage is temporary: the thyroid adapts and resumes its normal function within a few days.

On the other hand, in individuals with a pre-existing thyroid condition (such as Hashimoto's disease or Graves' disease), this effect can trigger or worsen an imbalance. This is why caution is advised for these populations.

Dietary excess vs. iatrogenic excess: an essential distinction

And that's where things get interesting. When we look at documented cases of iodine excess in France, almost all are linked to a specific cause: improperly dosed supplementation. Dietary supplements taken in excessive amounts, or medications containing iodine (such as amiodarone, a cardiac antiarrhythmic that contains a large amount of it).

According to a review published in ScienceDirect In 2021, French nutrivigilance data reported only 4 cases of adverse effects related to excess dietary iodine in France (4). Four cases. Out of millions of consumers.

And a meta-analysis published in PubMed In 2019, it was confirmed that in healthy individuals without thyroid pathology, the tolerance to high iodine intake is much better than what precautionary recommendations suggest (5).

Specifically, here is the essential distinction that no one clearly makes:

• Iatrogenic excess (Medications, overdosed supplements): real and documented risk
• Overeating (seaweed consumed in reasonable quantities as part of a varied diet): extremely low risk for healthy individuals

To explore the relationship between algae and the thyroid, consult our Complete guide to edible seaweeds: dulse, wakame, sea lettuce.

What the numbers really say

Let's put things into perspective. Here are the data side by side:

Iodine deficiency in France: - Affects 43% of women of childbearing age (ANSES) (2) - Potentially concerns millions of people - Consequences: fatigue, cognitive disorders, pregnancy complications, goiter - Trend: increasing according to WHO (2024 report) (3)

Dietary iodine excess in France: - 4 documented cases of nutrivigilance (ScienceDirect, 2021) (4) - Concerns almost exclusively individuals with pre-existing conditions or excessive supplementation - Most cases are transient and reversible - Safety limit set at 600 µg/day by EFSA (2014) and ANSES (6)

Objectively speaking, the balance overwhelmingly leans towards deficiency as a major public health issue. While overconsumption should not be ignored, it remains a marginal phenomenon.

Dr. Reliquet's insight: "We do not consume enough iodine"

Dr. Vincent Reliquet is a French doctor whose clinical work supports the thesis of chronic under-consumption of iodine in France, with consequences far more extensive than generally acknowledged.

Clinical observations on thyroid patients

Dr. Vincent Reliquet is a French doctor whose work on iodine deserves to be known. Through his clinical observations and publications, he has developed a thesis that we at Biovie share: the French population is generally under-dosed in iodine, and this chronic under-consumption has far wider consequences than is generally acknowledged.

What is interesting about Dr. Reliquet's approach is that he does not merely note the deficiency. He observes in his thyroid patients that an iodine intake through natural sources, particularly seaweed, can help support thyroid function when it is integrated gradually and in a controlled manner.

Obviously, it is not about replacing medical treatment. But about providing the body with an essential raw material that it lacks.

Why Dr. Reliquet defends seaweeds

Dr. Reliquet makes a fundamental distinction between iodine from synthetic supplements and iodine from whole foods like seaweed. In a whole food, iodine is not isolated: it is accompanied by a whole array of minerals, trace elements, and bioactive compounds that modulate its absorption and use by the body.

This is what we have also observed empirically at Biovie for 18 years. The feedback from our customers who incorporate algae into their daily diet is remarkably positive, and cases of iodine-related issues are almost nonexistent when dosages are respected.

The Japanese populations of Okinawa, who have been consuming seaweed daily for generations, are among the longest-living in the world. Their iodine intake is much higher than European recommendations, yet thyroid disorders are rare there. This doesn't prove everything, but it does invite us to question our European hesitancy towards this ancestral food. To delve deeper into this fascinating topic, check out our article on The Iodine Secret of Okinawa's Centenarians.

Seaweed: The Natural Solution for a Balanced Iodine Intake

Seaweeds provide a naturally bioavailable source of iodine, accompanied by mineral cofactors that facilitate its absorption. They represent the most complete solution to address iodine deficiency without the risk of excess, provided that the dosages per species are respected.

Iodine content by type of seaweed: practical measurements

Frankly, this is one of the subjects where our field expertise truly makes a difference. After 18 years of working with seaweed, visiting production farms, and analyzing batches, we have a precise understanding of what each species contributes in terms of iodine.

Here are the practical data that you won't find anywhere else presented so clearly:

• Kombu (Laminaria) : it is the champion of iodine, with levels ranging from 1,500 to 8,000 µg per 1 g of dry weight. A small amount is enough, and that's precisely why it is measured carefully. A pinch in a broth or soup, and your daily intake is more than covered.