“Vitamin A deficiency is one of the major nutritional problems in the world, most common in developing countries. Food fortification is a recognized approach to supply vitamins and minerals to needed populations. Vegetable cooking oils were previously suggested by us as a carrier for vitamin A fortification. Fortification of cooking oil with beta-carotene could also be a strategy to prevent vitamin A deficiency.” (Dutra-de-Oliveira, et al., International Journal of Food Science and Nutrition, 1998 May; http://www.ncbi.nlm.nih.gov/pubmed/10616662)
The above-cited study examined whether beta-carotene could be added to cooking oil in order to supply this essential micronutrient to disadvantaged populations in developing nations. As I’ve mentioned in a previous post, Guatemala fortifies sugar with vitamin A, and they do so by means of a small amount of food oil. Several oil types have been tested and found to be appropriate: “corn, palm, soya bean, cottonseed, and sunflower.” (http://archive.unu.edu/unupress/food/V192e/ch07.htm) These same types of oil could be fortified with vitamin A or beta-carotene for direct consumption, rather than adding the oil to sugar.
But when vitamin A and beta-carotene are compared, the latter has a much higher safe upper limit. It is difficult to consume too much beta-carotene, and the main detrimental effect is a yellowish or orange pigmentation of the skin, especially of the palms and soles of the feet, which gradually diminishes when the excessive beta-carotene consumption stops. On the other hand, excessive intake of vitamin A results in a long list of different side effects, some of them quite severe, including: vision problems, bone pain and bone swelling, bone developmental problems in infants and children, liver damage, nausea, vomiting, dizziness, and more. (http://www.nlm.nih.gov/medlineplus/ency/article/000350.htm) In addition, large doses of vitamin A in pregnant women can cause birth defects. (Vitamin A: MedlinePlus; http://www.nlm.nih.gov/medlineplus/ency/article/002400.htm)
Supplementation of cooking oil with beta-carotene is much safer than with vitamin A, because the possibility of excessive intake cannot be entirely avoided. But whereas excessive intake of beta-carotene has only the mild and reversible effect of skin discoloration, the effects of vitamin A overdose can be severe and even irreversible (e.g. birth defects). So beta-carotene is the obvious choice for the fortification of cooking oil.
One important issue, though, is that cooking oil is often heated to high temperatures before being consumed. Temperature affects cooking oil in three ways. First, some oils are not heated at all before being consumed, for example, oil added to salads. Second, some oils are heated only to boiling temperatures, such as oils added to soups and stews. Third, some oils are heated to high temperatures, such as oils used for frying. If heating reduces the effective amount of the supplemental beta-carotene, then an increase in the supplement amount would be needed. But since some of the oil is not heated, the amount of the supplement must not be excessive.
The above-cited study found that at 100 degrees centigrade (boiling temperature), there was no decrease in beta-carotene, and at 170 degrees, a medium temperature for frying, beta-carotene retention was 65% (a 35% reduction). The authors of the study concluded the following: “beta-carotene added to soybean oil showed good stability to heat and its bioconversion to vitamin A was shown in rat assays. beta-carotene mixed well with edible soybean oil and the fortified cooking oil showed potential as a carrier to be used for the prevention of vitamin A deficiency.” (Dutra-de-Oliveira, et al., International Journal of Food Science and Nutrition, 1998 May; http://www.ncbi.nlm.nih.gov/pubmed/10616662).
I propose a program whereby cooking oil is supplemented with beta-carotene, especially in developing nations with high incidence of childhood blindness due to vitamin A deficiency. How much beta-carotene should be used is a difficult question.
When we compare beta-carotene in food versus vitamin A in food, the vitamin A (retinol) is absorbed much more efficiently in the digestive system. It is for this reason that 12 times as much beta-carotene (and 24 times as much of other carotenoids) is needed, compared to vitamin A. But when beta-carotene is consumed in the form of a supplement (e.g. in a pill), only twice as much beta-carotene is needed compared to vitamin A. See this post for more information on that point.
For supplementation, 2 mcg of beta-carotene is the same as 1 mcg of vitamin A (retinol), because beta-carotene in supplement form is absorbed by the digestive system much more efficiently than in food form. To obtain 100 RAE (retinol activity equivalents), the oil would need to have 200 mcg of beta-carotene. But if the oil is used for cooking, then that number would need to be increased further: 300 mcg of beta-carotene times 65% equals 195 mcg of beta-carotene, taking into account the 65% reduction when the oil is heated. So if we decide that 100 RAE is needed, the oil should be supplemented with 300 mcg of beta-carotene. Then, too, we must consider, if the oil is not heated, whether the total dose of 300 mcg of beta-carotene (which is 150 RAE) would be too high.
Here is a discussion of the RDA as well as the UL (safe upper limit) for vitamin A in RAE units. But note that the UL only applies to vitamin A; carotenoids are safe at even higher levels. Even so, let’s consider that the maximum intake of beta-carotene from cooking oil should be no higher than the UL for retinol.
Another issue is that persons of various ages do not consume the same calories per day, and therefore they do not consume the same amount of cooking oil per day. Let’s consider the number of tablespoons of cooking oil that might be consumed by a range of different ages, beginning with adults.
One tablespoon is 13.6 grams. If you examine a bottle of cooking oil, it may say something like: “1 tbsp (14 g) 120 cal”. But the USDA nutrient database gives the value of 13.6 grams and 120 kcal for one tablespoon; 14 grams gives us 124 kcal.
The reason that we are considering the calories (kcal) in the cooking oil is that it gives us a way to gauge the upper limit of cooking oil intake, so that we can then determine the upper limit of beta-carotene intake. If a person has a 3000 kcal diet, ordinarily about 30% of those calories should be from fat; which is 900 kcal, and therefore 7.5 tbsp of oil. However, some persons consume more fat in their diet than they should. An unhealthy — but not entirely uncommon — diet might be 40 or even 50% fat. So at 1500 kcal, the total oil would be 12.5 tablespoons. As a worst case scenario, if an adult has a 3000 kcal diet, and they obtain half of those fat calories entirely from the supplemented cooking oil — a situation that should be rare or non-existent — the amount of beta-carotene should still be at or below the safe UL for an adult, which is 3000 RAE. So if we divide 3000 by 12.5, we end up with the maximum RAE for 1 tablespoon of oil of 240 RAE. The supplemental beta-carotene in the cooking oil should therefore be less than 240 RAE per tablespoon.
But what about the dosage for children? If we again use a worst case scenario of 50% of total calories from this cooking oil, and we stay below the safe upper limits for children of various ages, the result is that 150 RAE per tablespoon of cooking oil remains at or below the safe UL for all ages, from birth through childhood through the teenage years. Also, recall that this safe UL is for vitamin A; the safe UL for beta-carotene is much higher. Therefore, 150 RAE per tablespoon is not excessive.
At 150 RAE, some adults will not receive sufficient amounts of beta-carotene through cooking oil alone. At least 4 tbsp per day (480 kcal) would be needed to reach 600 RAE for an adult. This might be more cooking oil than some adults would consume, especially on a daily basis. However, the goal of this program is to reduce childhood blindness and mortality due to vitamin A deficiency.
To reach 150 RAE per tablespoon, we need 300 mcg of beta-carotene. This does not account for the possible reduction in the RAE due to high temperature cooking. With that reduction, 300 mcg gives us just under 100 RAE (taking into account the reduction to 65% and the 2:1 ratio of beta-carotene to retinol needed to convert mcg to RAE). There is no problem with excessive beta-carotene with this reduction. But it does reduce the RAE significantly.
To address this problem, we could raise the mcg of beta-carotene even higher, to 460 mcg. This would give us 230 RAE, which when reduced by 65% is almost exactly 150 RAE. But if the oil is not heated to frying temperatures, and there is no reduction, then the RAE would remain at 230 RAE. This level is about the maximum that we determined for adults, but it is above the upper limit we prudently chose for children.
So instead, I suggest keeping the level of beta-carotene at 300 mcg (150 RAE) per tablespoon. Parents can be instructed to use the oil in food that is not fried, or to give the oil to young children as a type of preventative medicine. A dose of 2 tablespoons per day, taken alone or mixed cold with food, should be sufficient to prevent vitamin A deficiency (VAD) blindness in children of all ages. However, even with the reduction to 100 RAE when heated, that amount is probably still sufficient to reduce the incidence of VAD blindness in the developing world significantly.
If each tablespoon of oil has 150 RAE, which is 300 mcg of beta-carotene, how much beta-carotene must be added to each liter (or quart) of oil? One liter is 67.6 US tablespoons. So each liter of oil would have 10,140 RAE, which is 20,280 mcg of beta-carotene. This amount is 20.28 milligrams of beta-carotene per liter. A US liquid quart is 64 tablespoons, which gives us 19.2 milligrams of beta-carotene. Therefore, 20 milligrams of beta-carotene per liter or quart should suffice for either unit of measure.