Say iodine and most people think of goiter; the big bulge that people with severe iodine deficiency develop in their necks. The bulge is nothing more than an enlarged thyroid gland. Normally, as blood flows through the thyroid, it absorbs all the iodine it needs but if there’s not enough iodine to be found, the thyroid grows in size attempting to grab whatever iodine it can find in the blood stream; a larger thyroid = more thyroid tissue trying to sponge up more of this precious mineral.
Severe iodine deficiency is still a major nutritional deficiency concern in some parts of the world. Because the iodine content of soil varies geographically, the iodine content of food is inconsistent & unreliable for the most part. Goiter used to be a real concern in Canada too before iodine was added to table salt which virtually eliminated goiter, the most extreme form of iodine deficiency.
Iodine and the brain
Iodine is crucial for healthy thyroid function. In the thyroid gland, iodine combines with the amino acid tyrosine to form the thyroid hormones T4 (thyroxine) and T3 (triiodothyronine); a mouthful for sure. T3 is the active form and basically does it all.
T3 regulates physical growth and development in both fetuses and infants, promotes intellectual/brain development, regulates metabolic rate, body temperature, protein metabolism, heart rate, lung function, testosterone & estrogen production, immune function, neurotransmitter production and more (1). Almost all of your body’s functions in nearly every tissue rely on thyroid hormones. Their actions and influence are so wide ranging that you cannot live without them.
Iodine is a nutrient of concern during pregnancy & beyond because of its role in infant and child growth and brain development. Even a modest deficiency, long before goiter shows up, can result in a loss of 10-15 IQ points (2). This is why prenatal supplements have extra iodine and should not be overlooked.
Because iodine is crucial for a healthy and happy thyroid, and therefore T4 & T3 production & function, this precious mineral has a big role in good mental health. Iodine helps ensure that there’s enough T4 and T3 in the brain to help it activate key neurotransmitters such as dopamine, norepinepherine, serotonin, GABA, acetylcholine and epinepherine. Without out enough T4 & T3, people may experience insomnia, fatigue, depression, and difficulty concentrating and focusing.
Impact on mood
As hormones, T4 & T3 regulate gene expression. Think of genes as a light switch and hormones as your hand; you use you hand to turn on, or turn off the switch. Similarly, hormones turn on, or turn off genes. Not consuming enough iodine can result in not having enough T4 & T3 to turn on the genes that regulate the very neurotransmitters that regulate your mood.
Serotonin: studies have shown that low levels of T3 results in low levels of serotonin which can lead to decreased mood/happiness, depression, changes in social behaviour, and increased anxiety (3)
Dopamine: T3 also regulates the action of dopamine (which is converted into norepinepherine/epinepherine) which affects memory, feelings of pleasure & reward, focus & attention, and improved behaviour and cognition (4)
GABA: GABA is the ‘zen’ neurotransmitter. Think of it as your brain’s natural benzo. T3 is needed for optimal GABA production and therefore helps you respond to stress better. Low T3 via low iodine intake can result in impaired GABA production and increased anxiety (5).
Acetylcholine: not as well known as other neurotransmitters, acetylcholine is need for learning and forming new memories. Low iodine intake and low T4 & T3 can result in low acetylcholine levels in the brain affecting cognition, memory, recall and mood.
What foods provide iodine?
- Fish (such as cod and tuna), seaweed, shrimp, and other seafood, which are generally rich in iodine.
- Dairy products (such as milk, yogurt, and cheese) are important sources of iodine in North American diets.
- Fruits and vegetables, which contain iodine, although the amount depends on the iodine in the soil where they grew and in any fertilizer that was used.
- Iodized salt, which is readily available in North America. Processed foods, however, such as canned soups, almost never contain iodized salt
Are you getting enough iodine?
Studies of North Americans suggest that the vast majority of people are technically consuming enough iodine to prevent a clinical deficiency (using urinary iodine excretion). The results below are from the ongoing Canadian Community Health Survey which suggests that most Canadians meet the World Health Organization’s goal of 0.79 to 1.57 micromolar/L (of urine). US studies have similar findings.
But not everyone is hitting the mark. About 22% of Canadians have a mild iodine deficiency and another 7% have a moderate deficiency. In other words, almost 1/3 of the population may be at risk of not reaping the full brain & mental health benefits of iodine and that’s a concern.
In medicine, when it comes to matters of nutrition, it’s assumed that if a person doesn’t have a classic nutrient deficiency, in this case goiter, then there’s nothing to worry about, but this is a very old school approach to nutritional biochemistry rooted in the concept of preventing deficiency-related diseases. The problem with this approach, is that it doesn’t take into consideration that people have different absolute requirements for any given nutrient. People don’t absorb nutrients to the same degree, and the field of nutrigenomics has shown us that a person’s unique genes affect their ability to use nutrients to their fullest extent and more.
Simply striving to prevent a deficiency may not be the best goal when it comes to your health, you may want to go beyond just crossing the finish line and go for gold. This is no less true when it comes to a nutrient like iodine, one which we assume everyone is getting/utilizing enough of especially when it comes to something a precious as your mental health.