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Vitamin A is required to prevent night blindness and xerophthalmia (dry-eye syndrome), as well as to reduce susceptibility to infection and an increased mortality rate from diseases such as measles and diarrhoea, particularly in infants and young children (Kopec et al, 2014). It is, therefore, essential that we have an adequate dietary intake of vitamin A.
Vitamin A deficiency
It has been estimated that globally nearly 1% of all preschool children suffer from vitamin A deficiency, the leading cause of childhood blindness.
In addition, nearly 8% of pregnant women all over the world are deficient in vitamin A. This means that they are less able to provide their developing unborn babies with vitamin A to promote healthy growth, particularly of the eyes and immune system.
Read: Moms-to-be may be lacking vit. A
Mothers who breastfeed also need to have an adequate vitamin A intake to ensure that their infants can benefit from a good supply of this protective vitamin (Kopec et al, 2014).
In South Africa it is estimated that 17% of preschool children and 19% of pregnant women are deficient in vitamin A (World Bank, 2014).
Dietary sources of vitamin A
There are two main sources of vitamin A in the human diet:
- Pre-formed vitamin A which is found only in animal foods such as liver, milk fat, eggs, and especially in cod and halibut liver oil.
In general, foods derived from animals are relatively expensive and often not part of the diet of economically disadvantaged populations.
- Provitamin A, in the form of the alpha- and beta-carotenoids, is found in dark green leafy vegetables like spinach, broccoli, and dark orange-coloured vegetables and fruit including pumpkin, butternut, sweet potatoes, carrots, spanspek, apricots, mango, and peaches.
To be effective, these carotenoids need to be transformed into active vitamin A in the human body. As these plants foods can be grown in vegetable gardens and small orchards, the carotenoids may be more accessible sources of vitamin A for economically disadvantaged communities. (Mahan et al, 2012)
Read: Carotenoids boost iron absorption
Dire need in South Africa
In South Africa, the need to boost vitamin A intake has been recognised for a long time, which is why our staple cereals (wheat flour and maize meal) are fortified with vitamin A together with vitamins B1, B2, niacin, folic acid, pyridoxine, and the minerals iron and zinc.
Infants are also usually given high doses of vitamin A as an immunity booster at one or more of their regular clinic visits during the postnatal period, as recommended by the WHO.
Read: Fortified foods don't make enough of a difference
Early studies showed that giving young children a dose of vitamin A as part of their measles treatment helps to lower mortality and decrease diarrhoea, herpes and respiratory tract infections such as pneumonia (Coutsoudis et al, 1991).
In a more recent evaluation by Imdad and co-authors (2010) of 43 studies involving more than 200,000 children, the researchers concluded that vitamin A supplementation “is effective in reducing all-cause mortality by about 24% compared to no treatment” in children from 6 months to 5 years.
Novel combination of avocado and beta-carotene
The study published by Rachel Kopec and her team (2014), investigated what food combinations can be used to increase the uptake of beta-carotene and also to boost its conversion from a provitamin to actual vitamin A.
The foods used in this study were grated carrots (a rich course of beta- and alpha-carotene) and a special tomato sauce made from a novel variety of tomatoes, rich in beta-carotene.
Because it was previously established that the uptake of provitamin A from foods can be improved by adding some type of lipid (fat or oil) to the mixture, the researchers combined both the grated carrots and the novel beta-carotene-rich tomato sauce with mashed avocado.
Avocado is rich in lipids or fats, particularly monounsaturated fats, and it can easily be combined with grated carrots in a salad, while the tomato sauce can be eaten with sliced or mashed avocado.
Read: 5 surprising benefits of avocado
Twelve healthy volunteers participated in the study. After a 2 week period during which they did not eat foods rich in vitamin A or provitamin A, and an overnight fast, the test subjects had baseline blood samples taken.
They were then either given a test meal consisting of the grated carrots and avocado, or the tomato sauce and avocado. Blood samples were drawn at regular intervals up to 12 hours after the meal. The samples were analysed for vitamin A content and activity.
After the sampling, the participants once again went on their low-vitamin A diet for 2 weeks and then returned to do the second test where they were given the opposite test meal with blood sampling at baseline and for 12 hours after the meal (Kopek et al, 2014).
Results
Kopec and her team (2014) found that eating avocado, rich in healthy fats, increased the absorption of beta-carotene from the novel beta-carotene-rich tomato sauce 2,4 times.
Avocado also enhanced the uptake of beta- and alpha-carotene from grated carrots 6,6 and 4,8 times respectively.
Read: Why your brain needs fat
Probably the most encouraging result was the finding that eating avocado also improved the efficiency of conversion of the beta- and alpha-carotene to active vitamin A 4,6 times.
Conclusions
The authors concluded that the results of their study highlight how important it is for people who are at risk of vitamin A deficiency to eat foods that contain beta- or alpha carotene together with a lipid-rich food such as avocado, to improve absorption to a maximum and also boost the conversion of these two provitamins to vitamin A, especially in populations suffering from vitamin A deficiency.
In South Africa we have such a high incidence of vitamin A deficiency among our preschool children and pregnant mothers that we should encourage everyone to eat foods like avocado together with foods rich in beta-carotene including carrots, pumpkin and marog (a dark green leafy plant, popular as a vegetable in African societies).
Avocados are in season in winter (buy in bulk, cut in half and peel then pop into a ziploc bag and freeze for your summer supply), so let’s encourage all our pregnant mothers and young children to eat dishes that combine avocado and vegetables rich in beta-carotene, to boost their health and immunity.
Ask DietDoc: Ask our the author and our expert, Dr Ingrid van Heerden questions about diet and nutrition
Read more:
Get some vitamin A
Complete guide to vitamin A (retinol)
Carrot (Daucus carota)
References:
Coutsoudis A et al. 1991. Vitamin A supplementation reduces measles morbidity in young African children: a randomized, placebo-controlled, double-blind trial. American Journal of Clinical Nutrition, 54(5):890-5; Imdad A et al. 2010. Vitamin A supplementation for preventing morbidity and mortality in children from 6 months to 5 years of age. Chochrane Database Syst Rev. 8(12):CD008524; Kopec RE et al. (2014). Avocado consumption enhances human postprandial provitamin A absorption and conversion from a novel high-beta-carotene tomato sauce and from carrots. Journal of Nutrition, 144:1158-1166.; Mahan KL et al. (2012). Krause’s Food & the Nutrition Care Process. 13th Ed., Elsevier, USA; World Bank. 2014. Nutrition at a glance - South Africa. www.worldbank.org/nutrition/profiles
