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Vitamins

Thiamin, riboflavin and niacin

  • 3 things to know
  • AS 1

Overview

The roles and sources of thiamin, riboflavin and niacin in energy release, beriberi and pellagra, tryptophan as a niacin source, and the effects of excess.

What you need to know

Answer each one before you reveal it.

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Key term

What is beriberi?

Key term

What is the main function of thiamin (vitamin B1)?

Key term

Why is the thiamin requirement linked to energy intake?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is the main function of thiamin (vitamin B1)?

    Model answer

    Thiamin is a coenzyme needed to release energy from carbohydrate. Thiamin is also needed for normal nerve and heart function.

  2. 2

    Why is the thiamin requirement linked to energy intake?

    Model answer

    Thiamin is used in releasing energy from carbohydrate, so a higher energy intake needs more thiamin. DRVs for thiamin are therefore expressed per 1,000 kcal of energy.

  3. 3

    Name valuable food sources of thiamin.

    Model answer

    Pork, wholegrain cereals, peas, beans and nuts are good sources of thiamin. White and brown flour in the UK must by law be fortified with thiamin, so bread is an important source.

  4. 4

    What is beriberi?

    Model answer

    Beriberi is the thiamin deficiency disease. Dry beriberi damages the nerves, causing muscle weakness and wasting. Wet beriberi affects the heart, causing heart failure and fluid retention.

  5. 5

    Why was beriberi historically common where people ate mainly polished white rice?

    Model answer

    The polishing process removes the bran and germ of rice, which contain most of its thiamin. A diet based on polished rice therefore supplied too little thiamin.

  6. 6

    Why are high intakes of thiamin and riboflavin from food not harmful?

    Model answer

    Thiamin and riboflavin are water-soluble, so any excess is excreted in the urine. Excess riboflavin turns the urine bright yellow but causes no harm.

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