Thiamine and Folic Acid: How They Overlap

Quick answer

Thiamin (vitamin B1) and folate are B vitamins with different jobs: thiamin is a helper for the enzymes that release energy from food, and folate carries the pieces cells use to build DNA. Men need 1.2 mg of thiamin and women 1.1 mg a day, against 400 mcg DFE of folate. Heavy drinking lowers both.^1,2,3,4

Key facts

Men need 1.2 mg of thiamin a day and women 1.1 mg. Adults need 400 mcg DFE of folate.^1,2
US law requires folic acid in enriched bread, flour, cornmeal, pasta and rice, and many breads and cereals also have added thiamin.^5,6
An adult body holds only 25 to 30 mg of thiamin and 15 to 30 mg of folate, so both need a regular supply.^3,4
Thiamin has no upper limit. Folic acid has one, 1,000 mcg a day from supplements and fortified foods.^2,3
Long-term heavy drinking reduces how much thiamin the gut absorbs and how much the liver stores, and alcohol also speeds the loss of folate.^3,4

Two vitamins, two kinds of work

Thiamin, spelled thiamine in many places, is a water-soluble B vitamin. Inside cells it becomes thiamin diphosphate, a helper molecule that five enzymes need to break down sugars, amino acids and fats. About 80% of the thiamin in an adult is in this form, mostly in muscle, heart, brain, liver and kidneys.³

Folate works on the construction side. It carries single carbon units, which cells pass along when they build DNA and RNA, and it takes part in the step that makes thymidylate, a DNA building block. About half of the body's folate is held in the liver.⁴

So one vitamin serves the energy chemistry and the other serves cell copying. No source we read describes either one changing how the other is absorbed, and no trial we found tested the pair against a single vitamin.^3,4

What the evidence shows for each

These two statements are the ones our ingredient files grade for each vitamin. They describe what enough does, and neither implies that extra gives more.^7,8

Contributes to normal energy-yielding metabolism*^1,3,7

Moderate evidence

Thiamin is needed by the enzymes that release energy from food: as thiamin diphosphate, it is a cofactor for five enzymes that break down sugars, amino acids and fats. 'Contributes to normal energy-yielding metabolism' is the wording European regulators permit for thiamin after EFSA review. It does not mean extra thiamin gives more energy to someone who already gets enough.

Amount studied: Recommended intake: 1.2 mg a day for men and 1.1 mg for women, from all sources

Has a role in making DNA and in normal cell division*^2,4,8

Moderate evidence

A long-established role of the vitamin. NIH describes folate as needed to make DNA and other genetic material and for cells to divide, and the EU, after review by its food safety authority, permits the statement that folate has a role in the process of cell division. It describes what folate does at recommended intakes, not an added effect from larger amounts.

Amount studied: Recommended intake: 400 mcg DFE a day for adults, from all sources

Where they meet in food

In the United States, enriched bread, flour, cornmeal, pasta and rice must have folic acid added, and many breads and cereals also have added thiamin, riboflavin and niacin.^5,6,9,10

That overlap means the same bowl of fortified cereal or slice of enriched bread can supply both. It also means a person who eats few grain foods, or who eats unenriched ones, may fall short of both at once. White rice that is not enriched has one tenth of the thiamin of brown rice.^3,6

Heat and water reduce thiamin. Bread has 20% to 30% less than its raw ingredients, pasteurizing milk removes up to 20%, and thiamin dissolves into cooking water that is poured away.³

Folate is also found in beef liver, leafy vegetables, beans, citrus and nuts, and thiamin in pork, fish, black beans, seeds and nuts. A varied diet with some whole grains and legumes tends to carry both.^1,2

How the body handles each

Thiamin and folate in the body^{2,3,4,11,12,13}
	Thiamin	Folate
Recommended daily amount, adults	1.1 mg (women), 1.2 mg (men)	400 mcg DFE
Share absorbed	More than 95% at usual intakes, a smaller share above about 5 mg a day	At least 85% of folic acid with food; about half of food folate
Body store	25 to 30 mg	15 to 30 mg
How fast stores fall	Can run down after about 3 weeks with none in the diet	Blood folate falls quickly once supplements stop
Upper limit	None set	1,000 mcg of folic acid from supplements and fortified foods

In both cases the small body store is the point. Neither vitamin builds up the way vitamin B12 does, so a steady daily supply matters more than the clock time of any one dose.^3,4

What’s in ours

Men's Multi: Vitamin B1, 7 mg per serving, from the label

What’s in ours

Men's Multi: Folate, 680 mcg DFE (400 mcg Folic Acid) per serving, from the label

On a Supplement Facts panel, thiamin may be printed as Vitamin B1 or as thiamine, and folate is printed in mcg DFE.^3,4

Drinking, medicines and who should ask first

Alcohol is the one factor both sources put on the same page. Heavy drinking over a long time lowers how much thiamin the gut absorbs and the liver stores, and NIH says it appears to be the most common cause of thiamin deficiency in highly industrialized countries. Alcohol also interferes with folate absorption and speeds its loss.^3,4

Alcohol interferes with folate absorption and speeds its loss. In healthy men, 8 ounces of red wine or 2.7 ounces of vodka a day for 2 weeks lowered blood folate.⁴

People who drink heavily, or who are recovering, should ask a doctor about these vitamins instead of choosing doses themselves. NIH describes guidelines for the most serious thiamin shortfall that call for high doses, preferably given into a vein, under medical care, and notes that oral supplements might not be enough.^3,12

Your doctor may want to check on you

Furosemide, a loop diuretic, has been linked in research to lower thiamin levels, possibly low enough to be deficient, because more thiamin is lost in urine. NIH says people who take it regularly should discuss their thiamin status with their health care providers.^1,3,14

Reported in studies

Ask your pharmacist or doctor first

Folate supplements could interfere with methotrexate when it is used for cancer, and the methotrexate label says to take products containing folic acid then only if a doctor directs it. When methotrexate is used for rheumatoid arthritis, psoriasis or polyarticular juvenile idiopathic arthritis, the same label tells prescribers to give folic acid or folinic acid to reduce side effects.^2,4,15,16

On the medicine's label

Ask first if you are pregnant with frequent or lasting vomiting. Cases of severe thiamin depletion have been reported in that situation.¹⁷
Ask first if you have had bariatric surgery, or take furosemide or chemotherapy with fluorouracil.³
Ask first if you plan to take more than 400 mcg of folic acid a day and have not had your B12 checked.⁴
Do not use thiamin if you have ever had an allergic reaction to it, including to a thiamin injection.¹²

Questions people ask

Should thiamine and folic acid be taken together?

They are routinely combined in B complex products and multivitamins, and the sources we read do not describe either one affecting how the other is absorbed. Take them with food or without, as suits you, since neither source names a best time.^3,4

Is thiamine the same as vitamin B1?

Yes. Thiamin, thiamine and vitamin B1 are three names for the same vitamin. Supplements usually use thiamin mononitrate or thiamin hydrochloride.^1,3

Is there a limit for thiamine and folic acid?

Thiamin has no set upper limit because no harm has been reported from high intakes, although absorption falls above about 5 mg a day. Folic acid does have one, 1,000 mcg a day from supplements and fortified foods.^2,3,11

Does drinking alcohol lower both vitamins?

Yes, according to NIH. Long-term heavy drinking lowers how much thiamin is absorbed and stored, and alcohol interferes with folate absorption. Anyone who drinks heavily should ask a doctor before relying on supplements.^3,4

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*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.