Vitamin A equivalency of β-carotene (VEB) is defined as the amount of ingested β-carotene in μg that is absorbed and converted into 1 μg retinol (vitamin A) in the human body. The objective of the present review was to discuss the different estimates for VEB in various types of dietary food matrices. Different methods are discussed such as mass balance, dose–response and isotopic labelling. The VEB is currently estimated by the US Institute of Medicine (IOM) as 12:1 in a mixed diet and 2:1 in oil. For humans consuming β-carotene dissolved in oil, a VEB between 2:1 and 4:1 is feasible. A VEB of approximately 4:1 is applicable for biofortified cassava, yellow maize and Golden Rice, which are specially bred for human consumption in developing countries. We propose a range of 9:1–16:1 for VEB in a mixed diet that encompasses the IOM VEB of 12:1 and is realistic for a Western diet under Western conditions. For a ‘prudent’ (i.e. non-Western) diet including a variety of commonly consumed vegetables, a VEB could range from 9:1 to 28:1 in a mixed diet.

The objective was to quantify the vitamin A equivalency of β-carotene in two diets using a dual-isotope dilution technique and the apparent β-carotene absorption as measured by the oral–faecal balance technique. Seventeen healthy adults with an ileostomy completed the 4-week diet-controlled, cross-over intervention study. Each subject followed both diets for 2 weeks: a diet containing vegetables low in β-carotene content with supplemental β-carotene in salad dressing oil (‘oil diet’; mean β-carotene intake 3·1 mg/d) and a diet containing vegetables and fruits high in β-carotene content (‘mixed diet’; mean β-carotene intake 7·6 mg/d). Daily each subject consumed a mean of 190 μg [13C10]β-carotene and 195 μg [13C10]retinyl palmitate in oil capsules. The vitamin A equivalency of β-carotene was calculated as the dose-corrected ratio of [13C5]retinol to [13C10]retinol in serum. Apparent absorption of β-carotene was determined with oral–faecal balance. Isotopic data quantified a vitamin A equivalency of [13C10]β-carotene in oil of 3·6:1 (95 % CI 2·8, 4·6) regardless of dietary matrices differences. The apparent absorption of (labelled and dietary) β-carotene from the ‘oil diet’ (30 %) was 1·9-fold higher than from the ‘mixed diet’ (16 %). This extrinsic labelling technique can measure precisely the vitamin A equivalency of β-carotene in oil capsules, but it does not represent the effect of different dietary matrices.

Data on the vitamin A equivalency of β-carotene in food are inconsistent. We quantified the vitamin A equivalency (μg) of β-carotene in two diets using the dual-isotope dilution technique and the oral–faecal balance technique. A diet-controlled, cross-over intervention study was conducted in twenty-four healthy adults. Each subject followed two diets for 3 weeks each: a diet containing vegetables low in β-carotene with supplemental β-carotene in salad dressing oil (‘oil diet’) and a diet containing vegetables and fruits high in β-carotene (‘mixed diet’). During all 6 weeks, each subject daily consumed a mean of 55 (sd 0·5) μg [13C10]β-carotene and 55 (sd 0·5) μg [13C10]retinyl palmitate in oil capsules. The vitamin A equivalency of β-carotene was calculated as the dose-corrected ratio of [13C5]retinol to [13C10]retinol in serum and from apparent absorption by oral–faecal balance. Isotopic data quantified a vitamin A equivalency of [13C10]β-carotene in oil of 3·4 μg (95 % CI 2·8, 3·9), thus the bio-efficacy of the β-carotene in oil was 28 % in the presence of both diets. However, data from oral–faecal balance estimated vitamin A equivalency as 6:1 μg (95 % CI 4, 7) for β-carotene in the ‘oil diet’. β-Carotene in the ‘oil diet’ had 2·9-fold higher vitamin A equivalency than β-carotene in the ‘mixed diet’. In conclusion, this extrinsic labelling technique cannot measure effects of mixed vegetables and fruits matrices, but can measure precisely the vitamin A equivalency of the β-carotene in oil capsules.