Iodised salt use before pregnancy and thyroid problems in pregnant women
What it found
Women who used iodised salt for at least two years before getting pregnant had far fewer thyroid problems during pregnancy.
Starting iodised salt only after becoming pregnant did not offer the same protection.
What they found
Studies in people
Thyroid failure rates
Among women who used iodised salt for at least two years before pregnancy, 6.4% developed thyroid underactivity. For those who started using it only when pregnant, the rate was almost six times higher at 36.8%.
Type of thyroid problem
Most women who developed thyroid issues had low levels of a specific thyroid hormone but normal levels of the main control hormone. This happened in 16 out of the 18 affected women across both groups.
Iodine levels at start
At the beginning of the study, women who had used iodised salt longer had higher iodine in their urine. Their estimated daily iodine intake was about 190 micrograms compared to 105 micrograms for the short-term group.
Hormone levels over time
Throughout pregnancy, women in the long-term group consistently had higher levels of free thyroid hormone and lower levels of the control hormone compared to the short-term group.
What the authors conclude
- They conclude that using iodised salt for a long time before pregnancy greatly lowers the chance of thyroid underactivity during gestation.
- They suggest this happens because prolonged use nearly restores the iodine stores inside the thyroid gland.
- The authors advise that starting iodised salt only after becoming pregnant does not seem to protect against thyroid failure.
How it was done
Mild iodine shortage during pregnancy can cause thyroid underactivity in mothers and affect a baby's brain development. In Europe, fewer than half of pregnant women take iodine supplements, so iodised salt is often their only source of extra iodine.
Researchers followed 100 pregnant women living in an area with mild iodine shortage. Sixty-two women had used iodised salt for at least two years before pregnancy, while 38 started using it only when they became pregnant. The team checked their thyroid function twice each trimester throughout the pregnancy.
What it can’t tell you
- This study followed women over time rather than randomly assigning them to groups, so it cannot prove that iodised salt alone caused the difference in thyroid outcomes.
- Other habits or differences between the two groups of women might partly explain the results.
Who paid
- Authors work at
- Policlinico Universitario, Italy
The paper
- Title
- Iodine prophylaxis using iodized salt and risk of maternal thyroid failure in conditions of mild iodine deficiency
- Type
- Study
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Moleti M, Lo Presti VP, Campolo MC, et al (2008). Iodine prophylaxis using iodized salt and risk of maternal thyroid failure in conditions of mild iodine deficiency. The Journal of clinical endocrinology and metabolism. doi:10.1210/jc.2008-0352Free full textPubMed 18413422DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error