The thing about iodine is that it’s found mostly in the ocean. The problem with that is that most of us don’t live by the seaside. Like most micronutrients, iodine is something we have to get mostly from our food. Like vitamin A and iron deficiencies, an iodine deficiency is a major health risk, especially in low-income countries. From a public health perspective, iodine deficiencies are the main cause of brain injuries.
Iodine deficiency disorders
Iodine deficiency disorders (IDD) are a serious threat to the mental health and even survival of children in countries where iodine supplementation is not regulated. IDDs affect cognitive and motor development and can compromise children’s grades, leading to a 15-point drop in IQ. In adults, an iodine deficiency impairs productivity and hireability.
In pregnant women, it can cause gestational hypertension, and for the baby, everything from intellectual disabilities to cretinism. Around 50 million people worldwide suffer from some degree of iodine deficiency. In 2015, there were still 25 countries where the population did not get enough iodine (compared with 110 in 1993).
Iodine and women’s fertility
Beyond these major public health issues, a recently published study found that iodine deficiency also affects women’s fertility. The study showed that women with a moderate to severe iodine deficiency were 46% less likely to get pregnant than those with normal iodine levels. Furthermore, the study also highlighted iodine deficiencies in 30% of women of childbearing age and in school-age children in Europe.
In your body, the thyroid gland uses 30% of your iodine intake. Iodine is also found in the salivary glands, breasts, brain and gastric mucosa. The thyroid converts iodine into the hormones thyroxine (t4) and tri-iodothyronine (t3), which control a number of biochemical reactions in the body, including protein synthesis and enzymatic processes.
In people who suffer from hyperthyroidism, iodine blocks the secretion and synthesis of thyroid hormones.
An iodine deficiency and the resulting hypothyroidism lead to infertility, irregular menstruation and an increased risk of thyroid cancer. A lack of iodine is also one of the major factors in the development of goitre, a swelling of the thyroid gland. Because it’s located in the neck, goitre can affect your voice and ability to swallow.
It’s all well and good to talk about the thyroid gland, hormones and biochemical or enzyme reactions, but in concrete terms, the thyroid affects:
• Basic metabolism, namely the use of energy for blood circulation, brain, breathing, digesting and maintaining a body temperature of 37°C.
- Heart rate
- Body temperature
Symptoms of a weak thyroid
As a result, the signs and symptoms of a weak thyroid and possibly a lack of iodine include:
- Fatigue or lack of energy
- Unexplained weight gain
- Abnormally slow heartbeat
- Irritability and mood swings
- Trouble concentrating, confusion, memory loss
- Sensitivity to cold, especially in the morning
- Constipation, high cholesterol
- Hair loss, brittle nails, dry skin and infertility
The good news
Making sure the public gets enough iodine is a simple problem to fix: just add iodine to table salt. More and more countries are requiring that salt industry players add iodine to table salt. Today, all table salt sold in Canada must be iodized. However, sea salt does not carry this requirement. In this country, foods prepared with or containing added salt must also contain iodized salt or sea salt. Salt and sea salt that have not been iodized cannot legally be used in commercially prepared foods.
Our neighbours to the south are now confronted with a different problem. In the United States, table salt remains the main source of dietary iodine. For perfectly legitimate public health reasons, Americans (and Canadians) are being urged to reduce their salt intake, which they are doing when they cook their own food at home. But given that, unlike in Canada, there is no requirement that salt used in prepared foods and restaurants in the US be iodized, and that Americans are much more likely to eat out or have ready-made meals at home instead of eating home-cooked meals, their iodine levels are too low. The average iodine rates (measured in the urine) have dropped nearly 50% in the past 30 years, while the rate of iodine deficiency in pregnant women has risen from 1% to 7%.
How much iodine do we really need?
In Canada, the recommended daily iodine intake is:
- 90 μg (micrograms) for children aged 1 to 8
- 120 μg for children 9 to 13
- 150 μg for adults and adolescents 14 to 18
- 220 μg for pregnant women
- 290 μg for breastfeeding women
By eating a healthy diet that includes iodized salt, the average Canadian rarely needs iodine supplements, especially in high doses. However, it is important to be careful, as some foods, including some very healthy ones, block iodine absorption. These foods, known as goitrogens, include:
- Cruciferous vegetables: Brussels sprouts, cabbage, cauliflower, broccoli, kale, rutabaga, etc.
- Sweet potatoes
- Soybean seeds
Fortunately, their effect on iodine is lessened during cooking.
Iodine-rich foods include:
- Ocean fish
- Iodized table salt. While the sea salt you buy isn’t usually iodized, Herbamare aromatic sea salt contains kelp, an iodine-rich variety of seaweed.
- Dairy products (cottage cheese, yogurt and milk)
- Soy beans
Don’t worry: in Canada, it’s rare for people not to get enough iodine through their diet and table salt. But if the symptoms described above ring a bell for you, it’s a good idea to go see your doctor about it.
J.L. Mills et al. Hum Reprod. 2018 Jan 11