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Beta Carotene Conversion to Retinol

Beta-carotene is an orange-colored plant compound found in many fruits and vegetables, especially carrots. Like all other carotenoids, beta-carotene is a strong antioxidant capable of scavenging potentially harmful free radicals. Your body can convert beta-carotene into retinol -- commonly known as vitamin A -- if needed. The absorption and conversion of beta-carotene depends on many factors.

Rich Sources of Beta-Carotene

In addition to carrots, excellent sources of beta-carotene include watercress, pumpkins, winter squash, sweet potatoes, yams, apricots, papayas and mangoes. Dark green leafy vegetables such as spinach, kale and broccoli are also very good sources. The beta-carotene content within fresh produce varies greatly and depends on soil composition, time of year, ripeness and exposure to light and oxygen.

Conversion to Retinol

Is Too Much Beta Carotene Bad for You?

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Beta-carotene is called a provitamin A because your body can convert it into vitamin A or retinol when storage levels in your liver are low. Other carotenoids such as alpha-carotene also can be converted. Once in your small intestine, beta-carotene is cleaved or cut by a specific enzyme into two molecules of retinol. The conversion and absorption efficiency of retinol is relatively low -- between 9 percent and 22 percent -- and depends on many factors, such as the need for vitamin A, intestinal health, bile production and the amount of dietary fat in the intestines. Retinol is a fat-soluble vitamin, which means it needs some fat to be absorbed and stored in the body. If retinol is not needed by your body, beta-carotene is not cleaved in half within the small intestine. Instead, it’s absorbed intact and stored mainly within subcutaneous fat just beneath your skin.

Converting Units

Vitamin A used to be measured in international units, which was fine to account for retinol from animal-based foods or supplements, but a new measurement was created to account for your body’s ability to convert beta-carotene and other carotenoids into retinol equivalents. The conversion agreed upon by American researchers is 1 retinol equivalent equals either 3.33 international units of vitamin A activity directly from retinol or 10 international units of vitamin A activity from beta-carotene. In other words, retinol from meat or supplements is estimated to be three times more efficiently used as vitamin A by your body compared to beta-carotene from plants or supplements. This conversion is only an estimate because of the cleavage and absorption variability in the small intestine.

Safety of Beta-Carotene

Beta-Carotene While Pregnant

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Although beta-carotene is not the most efficient way of providing your body with vitamin A, it’s much safer than taking retinol directly. In large doses, retinol can be toxic, whereas beta-carotene is non-toxic in its natural form and not converted to vitamin A unless your body needs it. You cannot overdose on beta-carotene. The main downside to taking too much beta-carotene is that your skin may temporarily turn orange -- a condition called carotenosis.