There are four essential fat soluble vitamins that dogs need: Vitamin A, Vitamin D, Vitamin E, and Vitamin K.
Of these, vitamins A, D, and E aren’t expressed consistently in mg as vitamin K is. Instead, these vitamins are expressed in various units of measurement with IU, mcg, and mg being the most common.
The precise measure of one IU differs from vitamin to vitamin.
Glossary
• IU, International Unit
• RE, Retinol Equivalent
• RA, Retinol Activity
• RAE, Retinol Activity Equivalent
• mcg, Microgram
• mg, Milligram
• g, Gram
The Math
The answers provided in the below equations for vitamin A have been rounded up for your label comparison ease.
Vitamin A: Because we feed dogs their vitamin A primarily from animal sources, we are feeding them preformed vitamin A which is retinol and is the most biologically active form.
Vitamin A: 1 IU is the biological equivalent of 0.3 mcg retinol, or of 0.6 mcg beta-carotene
To convert vitamin A from IU to RE: IU/3.33 = RE
Example using a 50 lbs./23 kg typical adult dog: 1750 IU/3.33 = 525.5 RE
To convert vitamin A from RE to IU: RE * 3.33 = IU
Example using a 50 lbs./23 kg typical adult dog: 525.5 RE * 3.33 = 1750 IU
The answers provided in the below equations for vitamin D have been rounded up for your label comparison ease.
Vitamin D: We feed dogs vitamin D in their diet via D3 foods (animal sourced).
Vitamin D: 1 IU is the biological equivalent of 0.025 mcg cholecalciferol (D3).
To convert vitamin D from IU to mcg: IU * 0.025 = mcg
Example using a 50 lbs./23 kg typical adult dog: 189.2 IU * 0.025 = 4.73 mcg
To convert vitamin D from mcg to IU: mcg * 40 =IU
Example using a 50 lbs./23 kg typical adult dog: 4.73 mcg * 40 =189.2 IU
The answer provided in the below equations for vitamin E converted from mg to IU has been rounded down for your label comparison ease.
Vitamin E: Natural form of vitamin E is d-alpha tocopherol. It is also labeled as d-alpha tocopherol acetate, or d-alpha tocopherol succinate.
Natural Vitamin E: 1 IU is the biological equivalent of 0.67 mg d-alpha-tocopherol
To convert natural vitamin E from IU to mg: IU * 0.67 = mg
Example using a 50 lbs./23 kg typical adult dog: 15.75 IU * 0.67 = 10.55 mg.
To convert natural vitamin E from mg to IU: mg * 1.5 = IU
Example using a 50 lbs./23 kg typical adult dog: 10.5 mg * 1.5 = 15.75 IU