Already in the 1960s, scientists observed in birds and crocodiles that they had trouble reproducing due to certain synthetic chemicals. One of the most well-known cases is the drug diethylstilbestrol, a synthetic form of estrogen given to pregnant women in the USA to prevent miscarriage. Later, it was found that girls born to these mothers often developed a rare form of cancer and reproductive system abnormalities.
How can food disrupt the thyroid?
When talking about thyroid disruptors, it's not just about chemicals from industry, but also about some natural ingredients in food. In layman's terms, there are foods that are tough on the thyroid. The most well-known are goitrogenic compounds found in fruits, vegetables, nuts, and legumes. While they are generally beneficial for health, they can cause issues with the thyroid by interfering with the enzyme called thyroid peroxidase (TPO).
TPO is a sort of processing machine for iodine. Iodine, obtained from food (e.g., from sea salt or fish), needs to be processed by this enzyme into a form that the thyroid can use to make hormones, mainly T3 and T4. If TPO doesn't work properly, the body struggles to produce these hormones, which can lead to a slowed metabolism.
Goitrogenic substances are divided into three main groups: goitrins, thiocyanates, and flavonoids.
Goitrins and thiocyanates are formed in the plant when it is cut or chewed.
Flavonoids are antioxidants (otherwise very healthy!), which bacteria in our intestines can convert into goitrogenic substances.
Among the foods with the most goitrogens are cruciferous vegetables such as broccoli, cabbage, kohlrabi, Brussels sprouts, radishes, cauliflower, and horseradish. Soy, black and green tea are also on the list.
If we consume these plants moderately, there is no need to panic. A study from 2018 showed that in healthy individuals, consuming cruciferous vegetables does not cause thyroid problems, and in those with mild thyroid dysfunction, it can even be beneficial (e.g., antioxidants, fiber).
Dietary supplements - help or hindrance?
Some dietary supplements can also inhibit thyroid function. For example:
- Bacopa monnieri, a plant used in Ayurvedic medicine for memory enhancement.
- Algae Fucus and Laminaria are rich in iodine, but excessive intake can actually cause hormonal imbalance.
- Sea lettuce, a type of seaweed.
- Magnolia and pepper (specifically piperine from pepper) are often found in weight loss products, along with caffeine, green tea extract, and cinnamon. Excessive consumption of these ingredients can slightly slow down thyroid function.
- Selenium (a mineral mostly obtained from Brazil nuts) helps the thyroid in hormone production.
- Omega-3 fatty acids (e.g., from fish oil) reduce inflammation and support hormone balance.
A study from 2020 showed that individuals with low selenium levels have a 35% higher risk of thyroid issues.
Plastic Chemicals: a Silent but Stubborn Enemy
In the modern world, it's hard to escape plastic. The issue is that some types of plastic release substances that mimic or disrupt our hormones. The most well-known are bisphenol A (BPA) and phthalates. BPA is often found in can linings, bottles, and even thermal paper receipts. Phthalates soften plastic and are found in PVC products, toys, vinyl, and some packaging.
A study from 2016 showed that in individuals with the highest BPA levels in their blood, T4 thyroid hormone levels were about 10% lower compared to those with the lowest levels.
Therefore, it is advisable to store food and drinks in glass or stainless steel. Also, avoid heating food in plastic, especially in the microwave.
Pesticides: a Problem We Can't Ignore
Pesticides are another big group of endocrine disruptors. In 2014, the European Food Safety Agency (EFSA) tested 287 pesticides and found that more than a third have the potential to disrupt thyroid function.
Since thyroid hormones play a crucial role in brain development, the most sensitive groups are pregnant women and young children. Even small changes in hormone levels during pregnancy can be linked to lower IQ in children, as confirmed by an extensive Danish study from 2017 involving more than 80,000 mothers and children.
And remember: the thyroid is the only organ that must work neither too little nor too much. If it works too little, it's wrong. If it works too much, it's also ... Moderation in everything is first disrupted by the thyroid.
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