The Bottom Line

Although thiamin requirements are increased during pregnancy, pregnant women should be able to obtain an adequate amount through a varied diet and prenatal vitamins; additional supplementation is not necessary.

However, persistent vomiting, which is seen in women with severe nausea and vomiting of pregnancy, can lead to thiamin deficiency (and other nutrients) in a matter of weeks – causing serious health problems. Women need to call their health care provider (HCP) if they cannot keep food/fluids down.

Women who engage in chronic alcohol use while pregnant are very likely to be deficient in thiamin and other nutrients and experience a host of other health concerns. Click here for more information on alcohol use during pregnancy and for critical resources to stop drinking.

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Background

In adults, thiamin helps the body generate energy from nutrients and is necessary for the growth, development and function of cells, a healthy nervous system, and carbohydrate, protein, and fat metabolism. It is also an essential coenzyme in many biochemical pathways in the brain.

Increased Requirement

Thiamin requirements increase during pregnancy and lactation, with the fetus taking priority over the mother.

In the third trimester, concentrations of thiamin are twice as high in umbilical cord blood than in the mother’s blood.

One study found that even when breastfeeding women are deficient in thiamin, their milk concentrations are not; suggesting that the body gives thiamin to the milk first, before circulating in the mother.

A newborn with a clipped and cut umbilical cord.
Photo by Vidal Balielo Jr. from Pexels

Deficiency 

Thiamin deficiency does occur during pregnancy and can happen relatively quickly in certain conditions, therefore, eating a varied diet is important.

Deficiency can be seen in pregnant women (as well as the general population) with diabetes, chronic alcohol use, poor nutrition, strict dieting, persistent vomiting, prior bariatric surgery, HIV/AIDS, frequent intake of raw fish, and malabsorption disorders such as Crohn’s and celiac diseases.

Frequently eating raw fish or shellfish contributes to deficiency because raw fish contains enzymes that destroy thiamin. However, women are advised during pregnancy to avoid eating raw fish (even if frozen first).

In general, decreased thiamin levels can result in fatigue and metabolic issues, greatly affecting cells and various organ systems. Thiamin deficiency during pregnancy can cause intrauterine growth concerns and changes in glucose tolerance, which is necessary for proper blood sugar stabilization.

Severe thiamin deficiency can lead to beriberi (neurological and cardiovascular symptoms) and Wernicke's Encephapathy (WE), which can be seen in women with hyperemesis gravidarum. These conditions can be reversed with thiamin supplementation.

Women with severe NVP or who cannot retain fluids/foods need to contact their HCP.

It is estimated the incidence of WE in HG patients is on the rise since 2012, likely due to outpatient treatment. Further, thiamin is either not included or is inadequate in some brands of prenatal vitamins.

For women at risk of HG or currently experiencing HG, a prenatal vitamin with a minimum of 5 mg of thiamin has been recommended. Women should always talk to their HCP prior to taking any supplements.

Up to 80% of people with chronic alcoholism develop thiamin deficiency because not only does alcohol require thiamin for its metabolism, but ethanol also reduces absorption of thiamin and thiamin stores in the liver.

Supplementation

Pregnant women should be able to get all the thiamin they need from a varied diet. Prenatal vitamins typically provide about 1.5 milligrams (mg) of thiamin, above the daily recommendation of 1.4 mg during pregnancy.

There is not enough evidence to know what the effects might be of taking high doses of thiamin supplements, or what amount would constitute "high". It is still possible that excessive intakes of thiamin could have adverse effects, but there is a lack of reporting on this occurring, therefore an upper limit (maximum daily dose) has not been set.

Further, only a small amount of thiamin is absorbed (up to 30 mg), and since it is water-soluble, any extra is excreted through urine.

Food Sources

Foods rich in thiamin include yeast, legumes, pork, poultry, brown rice, eggs, soybeans, wholegrain breads, liver, peas, as well as fortified foods such as breakfast cereals.

Women with NVP have a variety of thiamin-enriched carbohydrate-based foods to choose from that may be tolerable enough to eat with nausea/vomiting.

Heating foods can reduce their thiamin content, but is also necessary for the proper cooking of poultry, pork, eggs, and other animal products containing thiamin.

Thiamin dissolves in water, so a significant amount of the vitamin is also lost through cooking water.

Processing also affects thiamin levels, as unenriched white rice has one- tenth the amount of thiamin compared to unenriched brown rice.

Dairy products and most fruits are not rich sources of thiamin (but possess other valuable nutrients).

Action

Women should aim for as much nutrition as possible with every meal, and eat a wide variety of foods.

Women who suffer from severe nausea/vomiting in early pregnancy and struggle to eat and/or get enough fluids need to call their HCP. Severe complications from malnutrition in early pregnancy can be easily avoided when caught and managed early.

References

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