Here is the complete guide to vitamin B1 (or thiamine), the “vitamin of mood and energy”, essential for turning your meals into fuel for your brain and muscles.

The complete guide to vitamin B1: the engine of your energy metabolism

Thiamine, or vitamin B1, is the very first vitamin of the B group to have been discovered. It acts as an “ignition key”: without it, your body cannot use the carbohydrates (sugars) you consume to produce energy.

For vegetarians and vegans, vitamin B1 is generally abundant, as it is found in the outer layers of grains, legumes, and nuts and seeds. However, it is extremely sensitive to heat and to certain “anti-vitamins” present in some of our favorite beverages. Here is how to optimize your reserves.

What is vitamin B1 actually used for in your body?

Vitamin B1 is essential for the functioning of tissues that consume a lot of energy, such as the brain and the heart:

Energy production: It allows the conversion of glucose into ATP (the energy unit of our cells). This is the main fuel for your muscles and nervous system.
Brain function: It contributes to the synthesis of acetylcholine, a neurotransmitter essential for memory and concentration.
Heart health: It helps maintain the tone of the heart muscle and ensures smooth nerve transmission to the heart.
Nerve protection: It contributes to the integrity of peripheral nerves.

Nutritional needs: an intake linked to your activity

The more carbohydrates you eat or the more physically active you are, the higher your vitamin B1 needs become.

Recommended nutritional intakes (RNI)

Profile	Recommended daily requirement
Adult man	1.3 mg
Adult woman	1.1 mg
Pregnant / breastfeeding woman	1.4 mg to 1.5 mg
Endurance athlete	2.0 mg to 3.0 mg

Did you know? Vitamin B1 is water-soluble and the body stores only very small amounts (around 30 mg, mainly in the muscles). A daily intake is therefore essential.

The fragility of vitamin B1 and its enemies

Vitamin B1 is one of the most unstable vitamins. It is degraded by:

Refining: 80% of vitamin B1 is lost when whole wheat is turned into white flour or brown rice into white rice.
Heat: Prolonged cooking at high temperature destroys it.
Alkaline pH: Adding baking soda to vegetable cooking water (to preserve color) destroys thiamine.
Tea and coffee: They contain tannins and caffeic acid that can inactivate vitamin B1 if consumed in excessive quantities during meals.

Top 10 best plant-based sources of vitamin B1

The secret to never running out? Eat “whole”.

Food	Serving	Vitamin B1 intake (mg)
1. Brewer’s yeast / nutritional yeast	1 tbsp	1.2 mg (90% of recommended intake)
2. Wheat germ	2 tbsp	0.4 mg
3. Sunflower seeds	30 g	0.4 mg
4. Pine nuts	30 g	0.35 mg
5. Oat flakes	50 g	0.3 mg
6. Brown rice (cooked)	150 g	0.25 mg
7. Split peas / Lentils (cooked)	150 g	0.2 mg
8. Macadamia nuts	30 g	0.2 mg
9. Pistachios	30 g	0.2 mg
10. Whole sourdough bread	2 slices	0.15 mg

Signs of deficiency: fatigue and irritability

A mild deficiency is common and manifests through symptoms often attributed to stress:

Physical and mental fatigue: Feeling of having an “empty battery”.
Irritability and sleep disorders: Difficulty managing emotions.
Loss of appetite and digestive disorders: Nausea or constipation.
Difficulty concentrating: Memory lapses and mental slowness.

Note: Severe deficiency (beriberi) has become rare but may occur in cases of chronic alcoholism or diets based exclusively on ultra-refined products.

FAQ: common questions about vitamin B1

Why should athletes monitor B1?

Because they burn a lot of sugar during exercise. Without enough B1, lactic acid accumulates more quickly in the muscles, leading to early fatigue and cramps.

Does white rice contain vitamin B1?

Very little. White rice is rice from which the bran and germ have been removed, where thiamine is located. If you eat a lot of rice, choose brown rice or “parboiled” rice, because the parboiling process forces vitamins to migrate toward the center of the grain.

Can you take too much vitamin B1?

No. Because it is water-soluble, excess is eliminated in urine. There is no known toxicity for vitamin B1 when taken orally.

Is nutritional yeast really effective?

It is a true “superfood” for B1. Just one tablespoon on your pasta or salads covers almost the entire daily requirement of an adult. It is the number one ally for vegans.

Scientific references and sources

ANSES: Nutritional references for vitamin B1 (Updated 2021).
EFSA (European Food Safety Authority): “Scientific Opinion on Dietary Reference Values for thiamin”.
The American Journal of Clinical Nutrition: “Thiamin: a review of its role in energy metabolism”.
National Institutes of Health (NIH): Thiamin Fact Sheet for Health Professionals.
Linus Pauling Institute: “Thiamin – Micronutrient Information Center”.