01/31/2026
Thiamine (vitamin B1) is an essential, water-soluble vitamin involved in energy metabolism, nervous system function, and cardiovascular health. Pregnancy increases metabolic demand, which also increases the body’s requirement for thiamine. Historically, thiamine deficiency has been linked to serious conditions such as cardiac dysfunction, neurologic symptoms, and fluid imbalance. In pregnancy, inadequate thiamine status has been associated with hyperemesis, fatigue, cardiac strain, and adverse maternal outcomes.
In the mid-20th century, physician John Irwin proposed that subclinical thiamine deficiency played a role in pregnancy toxemia (now called preeclampsia). In his clinical observations, he reported improved pregnancy outcomes when higher-dose thiamine supplementation was used in the third trimester. Using a daily dose of approximately 100 mg, he documented an absence of conditions such as preeclampsia (then referred to as toxemia), hypertension, hemorrhage, prematurity, and fetal loss within his clinical population. He described these pregnancies as largely trouble-free and noted that the infants appeared particularly robust and healthy, reporting no observed adverse reactions to the supplementation. His observations and clinical rationale were later outlined in his book, The Natural Way to a Trouble-Free Pregnancy. While these observations were not conducted as modern randomized controlled trials, they raised important questions that remain relevant today, particularly given that:
•Thiamine requirements increase during pregnancy
•Thiamine deficiency can exist even with adequate calorie intake
•Thiamine is easily depleted by refined carbohydrates, stress, illness, and certain medications
•Thiamine is water-soluble and has a strong safety profile
