What is the normal range for B2? Understanding Your Riboflavin Levels

December 30, 2025 •

3 min read

According to the National Institutes of Health, the Recommended Dietary Allowance (RDA) for riboflavin (vitamin B2) is 1.3 mg for adult men and 1.1 mg for adult women. Understanding the normal range for B2 is key to maintaining proper metabolic function, energy production, and overall health.

Quick Summary

This guide explains the normal dietary intake and clinical testing ranges for vitamin B2, also known as riboflavin. It covers the Recommended Dietary Allowances (RDA) for different age groups, how riboflavin levels are measured through blood or urine tests, and the symptoms associated with deficiency.

Key Points

Daily Intake: The normal range for B2 is generally described by the Recommended Dietary Allowance (RDA) of 1.3 mg for adult men and 1.1 mg for adult women.
Clinical Testing: Standard tests for B2 deficiency include measuring the erythrocyte glutathione reductase activity coefficient (EGRAC) or a blood test for plasma riboflavin levels.
Signs of Deficiency: A shortage of riboflavin can cause skin lesions, angular cheilitis (cracks at mouth corners), sore tongue, and fatigue.
Dietary Sources: Excellent sources of riboflavin include meat (especially organ meat), dairy products, fortified cereals, and leafy green vegetables.
High-Dose Usage: High-dose riboflavin (e.g., 400 mg daily) is sometimes used to help prevent migraines, with a noticeable bright yellow urine being a harmless side effect.
Water-Soluble Vitamin: Because B2 is water-soluble, excess amounts are flushed out by the body, so consistent intake is more important than storing it.

Normal Dietary Intake for Riboflavin

For most healthy adults, the focus is on daily intake rather than blood concentration. The body's ability to store riboflavin is limited, so consistent daily consumption is important. The Recommended Dietary Allowance (RDA) varies by age and life stage.

Adult Recommended Dietary Allowances (RDA)

Adult Men (19+ years): 1.3 mg per day.
Adult Women (19+ years): 1.1 mg per day.
Pregnant Individuals: 1.4 mg per day.
Lactating Individuals: 1.6 mg per day.
Older Adults (70+ years): Needs are similar to younger adults, though some studies suggest a slightly higher requirement for older men to correct for age-related changes.

Children and Adolescent RDAs

Infants (0-6 months): 0.3 mg per day (Adequate Intake).
Infants (7-12 months): 0.4 mg per day (Adequate Intake).
Children (1-3 years): 0.5 mg per day.
Children (4-8 years): 0.6 mg per day.
Boys (9-13 years): 0.9 mg per day.
Girls (9-13 years): 0.9 mg per day.
Teenage Boys (14-18 years): 1.3 mg per day.
Teenage Girls (14-18 years): 1.0 mg per day.

Clinical Measurement of B2 Levels

For a clinical assessment, healthcare providers may order specific tests, which measure riboflavin status biochemically. These differ from the daily intake recommendations. The erythrocyte glutathione reductase activity coefficient (EGRAC) is a common diagnostic test. A normal EGRAC is typically less than 1.2.

Another approach is a blood test to measure plasma or serum riboflavin levels. Lab reference ranges can vary, but one source indicates a normal plasma range of 1–19 mcg/L. Urinary excretion can also be measured; a total excretion of at least 120 mcg/day is often considered adequate for a healthy adult.

Symptoms of B2 Deficiency (Ariboflavinosis)

While deficiency is rare in developed countries, it can occur in individuals with poor dietary habits, alcoholism, or certain medical conditions. Symptoms often affect the mouth, throat, and skin.

Common signs include:

Cracks and sores at the corners of the mouth (angular cheilitis).
A sore or inflamed tongue (glossitis), which may appear magenta.
Swelling of the mucous membranes in the mouth and throat.
Red, greasy, and scaly skin patches, particularly around the nose, ears, eyelids, and genital area.
Hair loss.
Anemia.
Fatigue and low energy.
Vision problems, such as light sensitivity or itchy, red eyes.
Cataracts in severe, prolonged cases.

Sources of Riboflavin and Comparison

To maintain a normal range for B2, it is crucial to consume a balanced diet rich in riboflavin. Good sources include dairy, meat, and fortified grains.

Riboflavin Sources Comparison Table


Food Source	Serving Size	Approximate Riboflavin Content	Notes
Beef Liver	3 oz cooked	3.5 mg	One of the most concentrated sources.
Fortified Cereal	1 cup	~1.5 mg	Content can vary greatly by brand.
Dairy Milk	1 cup	0.4 mg	Milk products are a primary dietary source.
Eggs	1 large	0.25 mg	Excellent source, especially the yolk.
Salmon	3 oz cooked	0.1 mg	A good source of multiple B vitamins.
Spinach	1 cup boiled	0.4 mg	Like other leafy greens, an important source.
Almonds	1 ounce	0.3 mg	Provides riboflavin and healthy fats.

Conclusion

Maintaining a normal range for B2 is essential for health, with specific Recommended Dietary Allowances established for different populations. Most people achieve a sufficient intake through a balanced diet rich in dairy, fortified cereals, eggs, and lean meats. For clinical assessment, healthcare providers may use tests like EGRAC or a blood draw, though these are less common due to the rarity of severe deficiency in many countries. Symptoms of deficiency are most often seen in individuals with limited dietary intake or other health issues, but are typically reversible with dietary changes or supplements. For those with migraines, high-dose riboflavin has shown potential therapeutic benefits. Always consult a healthcare professional for a personalized assessment of your nutritional needs. For more information from a reputable source, see the NIH fact sheet on Riboflavin.

Frequently Asked Questions

The Recommended Dietary Allowance (RDA) for an adult male aged 19 and older is 1.3 mg of riboflavin per day.

The Recommended Dietary Allowance (RDA) for an adult female aged 19 and older is 1.1 mg of riboflavin per day.

Symptoms of riboflavin deficiency often include cracked lips, sores at the corners of the mouth, a magenta-colored tongue, skin rashes, and fatigue.

A doctor can diagnose a riboflavin deficiency through clinical signs and may confirm it with a biochemical test, such as the Erythrocyte Glutathione Reductase Activity Coefficient (EGRAC) or by measuring plasma riboflavin levels.

Foods rich in riboflavin include dairy products like milk and cheese, eggs, lean meat, fortified cereals, and vegetables such as spinach and mushrooms.

Since riboflavin is a water-soluble vitamin, the body excretes excess amounts in the urine, so toxicity from food or supplements is very rare. High doses can cause harmless bright yellow urine.

Yes, the RDA for riboflavin increases during pregnancy to 1.4 mg per day to support maternal and fetal growth.