Why They Originally Added Iodine to Salt

December 13, 2025 •

5 min read

In the early 20th century, many people in regions far from the coast suffered from a swollen thyroid gland known as goiter due to iodine deficiency. This led to a remarkably simple yet effective public health solution: adding small amounts of iodine to table salt.

Quick Summary

This article explores the compelling public health reasons behind the original addition of iodine to salt, detailing how this intervention effectively addressed widespread goiter and preventable intellectual disabilities caused by iodine deficiency.

Key Points

Goiter was rampant: The initial drive to add iodine to salt was to combat endemic goiter, a visible and widespread thyroid enlargement caused by iodine deficiency, especially prevalent in inland areas like the U.S. 'goiter belt'.
Preventable brain damage: Iodine is essential for thyroid hormones needed for fetal and infant brain development; deficiency was the leading cause of preventable intellectual disabilities globally before fortification.
Salt is an ideal delivery vehicle: Salt was chosen for fortification because it is universally consumed, cheap to fortify, easily distributed, and does not spoil.
A simple public health triumph: The decision to iodize salt in the 1920s was a simple yet revolutionary public health initiative that dramatically improved public health outcomes, including cognitive function.
Global adoption and lasting impact: The success in early-adopting countries led the WHO and UNICEF to promote universal salt iodization, substantially reducing iodine deficiency disorders worldwide.
Continued vigilance is necessary: With changing dietary habits and less home cooking, public health officials emphasize the ongoing importance of consuming iodized salt to maintain sufficient iodine levels.

The 'Goiter Belt' and a Pervasive Deficiency

Before the 1920s, iodine deficiency was a major public health crisis, particularly in inland regions of the United States like the Great Lakes, Appalachians, and Northwest. This area became known as the "goiter belt" because of the alarmingly high number of people suffering from goiter, an enlargement of the thyroid gland visible in the neck. This condition was especially prevalent in Michigan, where studies in the 1910s and early 1920s found very high rates of thyromegaly among young men and school children.

Iodine is a trace mineral that the body cannot produce on its own. It is crucial for the thyroid gland to produce hormones that regulate metabolism, growth, and development. Naturally occurring iodine levels are highest in coastal areas where the element is present in seawater, but inland soils, and thus local crops and water, are often poor in this vital nutrient. This geographical disparity was the root cause of the widespread deficiency.

The Discovery and Early Prevention Efforts

The link between iodine and thyroid function was established by scientists in the late 19th century. Earlier, in the 1830s, a French chemist suggested using naturally iodized salt to combat goiter, but widespread adoption was limited by cost and concerns about potential side effects from high doses. However, a key turning point came in 1917, when U.S. physician David Marine conducted a successful prophylaxis program using iodine on over 2,100 schoolgirls in Ohio, demonstrating a significant reduction in goiter rates. His findings paved the way for a more general public health initiative.

In 1922, Dr. David Cowie of the University of Michigan advocated for adopting salt iodization as a national strategy, inspired by a successful Swiss program that began in the 1920s. Cowie secured support from the medical community and salt manufacturers to begin distributing iodized salt. The effort was a resounding success, first appearing on shelves in Michigan in 1924, followed by national distribution by companies like Morton Salt.

The Health Consequences of Iodine Deficiency

The health impact of iodine deficiency extends far beyond the cosmetic symptom of goiter. It is a spectrum of disorders (IDD) that particularly affects pregnant women, infants, and young children with severe consequences for neurological development.

Conditions Caused by Insufficient Iodine

Goiter: The most well-known symptom, where the thyroid gland enlarges in an attempt to capture more iodine to produce thyroid hormones.
Cretinism: Severe, chronic iodine deficiency in utero or infancy can lead to this condition, characterized by intellectual disability, developmental delays, and physical abnormalities.
Hypothyroidism: An underactive thyroid that causes metabolic dysfunction, leading to symptoms like fatigue, weight gain, constipation, and increased sensitivity to cold.
Cognitive Impairment: Even mild deficiency during pregnancy is associated with lower IQ scores and poorer cognitive function in children.
Pregnancy Complications: Low iodine levels in pregnant women increase the risk of miscarriage, stillbirth, and premature delivery.

Salt as the Ideal Vehicle

The public health campaign to add iodine to salt was so effective because salt was the perfect vehicle for nutrient delivery. It is a universal foodstuff, consumed regularly by most people regardless of socioeconomic status or geographical location. The technology for adding iodine was simple, and the cost was remarkably low—just a few cents per person annually. Furthermore, salt does not spoil, making it easy to manufacture, store, and distribute. The success of this strategy led to a dramatic drop in goiter rates in countries that adopted it, virtually eliminating the condition in many places.

Comparison of Iodized vs. Non-Iodized Salt


Feature	Iodized Salt	Non-Iodized Salt (e.g., Sea Salt, Kosher Salt)
Iodine Content	Contains added potassium iodide or potassium iodate.	Naturally contains very little or no iodine.
Primary Purpose	Fortified to provide a public health benefit, preventing iodine deficiency.	Primarily for flavor and texture, not for nutritional fortification.
Public Health Role	A vital tool in eliminating iodine deficiency disorders globally.	Does not contribute to iodine intake and can pose risks in deficient areas.
Common Use	A standard table salt used for everyday cooking and seasoning.	Often used for specific culinary purposes like pickling, or by those with certain health concerns or preferences.
Consideration for Intake	Reliable source for meeting daily iodine requirements.	Requires alternative iodine sources in the diet, such as fish, dairy, or supplements.

Global Impact and Continued Efforts

The success of salt iodization in countries like Switzerland and the United States inspired a global movement. Organizations such as the World Health Organization (WHO) and UNICEF promoted universal salt iodization as a key public health strategy. This led to a significant worldwide reduction in iodine deficiency disorders, although challenges remain in certain regions. The public health community must continue monitoring iodine levels in populations to ensure that this easily preventable deficiency does not resurface.

Conclusion

The original addition of iodine to salt was a strategic, cost-effective public health measure aimed at eradicating a devastating nutritional deficiency. By fortifying a commonly used food item, public health officials were able to prevent widespread goiter and significantly reduce intellectual and developmental disabilities caused by iodine deficiency. The program serves as a testament to how a small, deliberate change in the food supply can have a profound and lasting impact on the health and cognitive development of an entire population. While the success has been significant, ongoing surveillance and fortification efforts remain crucial to prevent its return.

The Legacy of Iodized Salt

Eradicated Goiter Belts: The fortification of salt with iodine successfully eliminated endemic goiter in formerly iodine-deficient regions like the U.S. Midwest.
Improved Cognitive Health: Studies have shown that the introduction of iodized salt led to a measurable increase in average IQ scores in formerly iodine-deficient populations.
Cost-Effective Solution: Salt iodization is one of the most inexpensive and effective public health interventions in history, costing mere cents per person annually.
Universal Delivery Method: The ubiquity of salt consumption made it an ideal vehicle for reaching a broad population across all socioeconomic backgrounds.
Ongoing Monitoring Needed: The decline in home cooking and rise of non-iodized salt in processed foods mean public health vigilance is still required to ensure adequate iodine intake.

Frequently Asked Questions

Without enough iodine, the thyroid gland cannot produce sufficient hormones, leading to a range of iodine deficiency disorders (IDD). These can include goiter (enlarged thyroid), hypothyroidism, and, most severely, cretinism and other permanent intellectual impairments, especially if the deficiency occurs during fetal and infant development.

The concept originated from European research, notably in Switzerland in the early 1920s, which followed earlier observations linking goiter prevalence to low iodine intake. The first commercial iodized salt was introduced in Michigan in the U.S. in 1924, inspired by successful trials by American physicians like David Cowie and David Marine.

No, salt iodization is not mandatory in the United States, but it is widely available and distributed. The majority of table salt sold in the U.S. is voluntarily iodized by manufacturers, although non-iodized salt is commonly used in processed and packaged foods.

While iodine naturally occurs in seawater, the amount present in sea salt is highly variable and often insufficient to meet daily dietary requirements. The process of manufacturing and refining sea salt can also reduce its iodine content.

For adults, the recommended daily dietary allowance of iodine is 150 micrograms (mcg). Pregnant and breastfeeding women have higher requirements to support fetal and infant development.

Yes, excessive iodine intake is possible and can cause thyroid problems, including goiter, thyroiditis, and hyperthyroidism, especially in susceptible individuals. However, toxicity is rare through normal dietary intake in iodized-sufficient areas and is more often associated with very high-dose supplements or medications.

Multiple studies indicate that the introduction of iodized salt significantly improved the cognitive function and average IQ of populations in formerly iodine-deficient areas. Correcting iodine deficiency, especially during critical periods of brain development in children and infants, resulted in substantial cognitive benefits.