Dietary Folate Equivalent (DFE) Conversion Guidelines

Conversion Factors

When synthetic folic acid is taken with food (e.g., fortified foods or supplements ingested with meals), 1 µg folic acid equals 1.7 µg DFE, reflecting a 1.7‑fold greater bioavailability compared with natural food folate. 1, 2, 3, 4, 5
When synthetic folic acid is taken on an empty stomach or administered intravenously, 1 µg folic acid equals 2.0 µg DFE, reflecting a 2‑fold greater bioavailability under these conditions. 1, 2, 3, 4, 5

An intravenous dose of 125–200 µg folic acid corresponds to 250–400 µg DFE. 1

The 1 mg (1,000 µg) upper intake limit applies only to synthetic folic acid, not to total DFE, to avoid masking vitamin B12 deficiency and the risk of irreversible neurological damage. 6, 7, 8

Vitamin C enhances folate bioavailability by reducing degradation of both natural folate coenzymes and synthetic folic acid in the stomach; this effect is already incorporated into the standard DFE conversion factors. 1

To determine the required folic acid dose for a target DFE when the supplement is taken with food, divide the DFE amount by 1.7.
To determine the required folic acid dose for a target DFE when the supplement is taken on an empty stomach or intravenously, divide the DFE amount by 2.0.
Example: Achieving 400 µg DFE from folic acid taken with food requires approximately 235 µg folic acid (400 ÷ 1.7). 1

1 µg dietary folate is equivalent to 0.6 µg folic acid from fortified foods or supplements taken with meals, reflecting a 1.7‑fold greater bioavailability of synthetic folic acid compared with natural food folate. [@1]
1 µg dietary folate is equivalent to 0.5 µg folic acid when the supplement is taken on an empty stomach or administered intravenously, reflecting a 2‑fold greater bioavailability of synthetic folic acid in these conditions. [@1]

1 µg synthetic folic acid ingested with food provides the nutritional value of 1.7 µg DFE. [@1]
1 µg synthetic folic acid taken on an empty stomach or intravenously provides the nutritional value of 2.0 µg DFE. [@1]

A 400 µg folic acid supplement taken with food corresponds to 680 µg DFE. [@1]
A 4 mg (4000 µg) folic acid dose used for neural‑tube‑defect (NTD) prevention corresponds to 6 800 µg DFE. [@2]
An intravenous folic acid dose of 125–200 µg corresponds to 250–400 µg DFE. [@1]

Ascorbic acid (vitamin C) enhances folate absorption by reducing degradation of both natural folate co‑enzymes and synthetic folic acid in the stomach; this effect is already incorporated into the standard DFE conversion factors. [@1]

The tolerable upper intake level of 1 mg (1000 µg) per day applies only to synthetic folic acid, not to total DFE, to prevent masking of vitamin B12 deficiency. [@2]