Did you know DNA influences your risk of vitamin A deficiency?
Carotenosis, vitamin A and genetics
“Daddy! Look at that orange boy.” Secretly hoping your 3-year-old is referring to body paint, you turn around and come face-to-face with a boy whose skin can only be described as yellow or orange. Carotenesis is actually a clinical condition, caused by eating too many carrots or other yellow, orange and red coloured vegetables containing beta-carotene. If your skin turns yellow in October, when you’ve been eating your fill of pumpkin pie, there’s no need for alarm, because carotenosis is reversible. However, yellow skin can sometimes signify something more serious. It could be a sign that your body can’t properly convert beta-carotene into active vitamin A.
Vitamin A is a group of compounds that includes retinol, retinal, retinoic acid and carotenoids. Animal sources of vitamin A contain retinol, a form that is ready to be used and is designated “preformed”. Plant sources contain carotenoids, or provitamin A. Provitamin A must be converted to an active form before the body can utilize it.
Beta-carotene is the most common carotenoid (provitamin A). Beta-carotene is converted to active vitamin A by an enzyme called beta-carotene oxygenase 1 (encoded by the BCO1 gene). The amount and activity of this enzyme dictate how much beta-carotene gets efficiently activated. Genetic variants in the BCO1 gene affect enzyme activity and can have drastic effects on vitamin A levels.
Four variants of BCO1 are linked to vitamin A levels, all of which decrease the conversion of beta-carotene. For example, inheriting one defective copy of the rs7501331 T variant can decrease your ability to convert beta-carotene by 32%. Similarly, the rs6564851 G variant is associated with higher beta-carotene levels in the blood, another sign of inefficient conversion. Surprisingly, these BCO1 variants are much more common than you might think. For example, almost half of us (44% of the population) carry at least one copy of the rs7501331 T variant. ‘Poor converters’ or people with at least one defective copy of BCO1 are at much higher risk of vitamin A deficiency, especially if they are vegetarian and rely on plant sources (beta-carotene).
Healthy eyes, immunity, red blood cell production, and the growth and maintenance of organs like the heart and lungs all require vitamin A. Vitamin A deficiency can be quite serious because it impacts many different systems of the body. While it is not as common in North America, vitamin A deficiency is quite common in the developing world and affects millions of children and pregnant women. Night blindness is one of the first symptoms to occur. Vitamin A deficiency is the main cause of preventable blindness in developing nations.
Other symptoms include decreased immune function, slow growth, high mortality in children, and poor pregnancy outcomes, such as birth defects. Because of these serious repercussions, vitamin A deficiency is a significant public health concern in the developing world. Thankfully, most of us in the developed world have access to cereal and fortified milk, or a small piece of beef liver, which is all you need to meet your daily vitamin A requirement. More details on how much vitamin A should be included in your diet and the best sources of vitamin A can be found at the end of this article.
In the developed world we may face the opposite problem, hypervitaminosis A, or vitamin A toxicity. This can cause dizziness, nausea, headaches, anorexia, anemia, and joint pain. In severe cases, it can result in liver damage, haemorrhage and even coma. Vitamin A toxicity can occur through overconsumption of preformed vitamin A as part of your diet, or more commonly as a supplement. This can be very dangerous during pregnancy, leading to birth defects. High vitamin A intake may also increase the risk of osteoporosis.
On the other hand, there’s mounting evidence that increased vitamin A intake may offer protection from cancer and age-related macular degeneration. If you love your orange fruits and vegetables, you will be happy to know that plant sources of provitamin A can’t cause hypervitominosis A. This is because the enzymes that convert carotenoids limit just how much active vitamin A is produced. The bottom line is, you should be extra cautious when taking vitamin A supplements if they contain preformed vitamin A. See table below for tolerable upper intake levels.
The growing popularity of alternative diets place genetic variants that can influence nutrient metabolism in a new light. BCO1 is one such example that can impact a vegan lifestyle, because when your diet doesn’t contain animal products, adequate processing of plant material becomes essential. If you are considering a vegan or vegetarian lifestyle, especially if your children are joining you, uncovering your BCO1 status will not only give you a head start but also peace of mind.
Recommended dietary allowances for vitamin A.
These recommended dietary allowances are listed as micrograms of retinol activity equivalents (mcg RAE) to account for the different bioactivities of retinol and provitamin A carotenoids. Each mcg RAE corresponds to 1 mcg retinol, 2 mcg of beta-carotene in oil, 12 mcg of “dietary” beta-carotene, or 24 mcg of the three other dietary provitamin-A carotenoids. For infants from birth to 12 months, an adequate intake is shown, which is equivalent to the mean intake of vitamin A in healthy, breastfed infants.
|0–6 months||400 mcg RAE||400 mcg RAE|
|7–12 months||500 mcg RAE||500 mcg RAE|
|1–3 years||300 mcg RAE||300 mcg RAE|
|4–8 years||400 mcg RAE||400 mcg RAE|
|9–13 years||600 mcg RAE||600 mcg RAE|
|14–18 years||900 mcg RAE||700 mcg RAE||750 mcg RAE||1,200 mcg RAE|
|19+ years||900 mcg RAE||700 mcg RAE||770 mcg RAE||1,300 mcg RAE|
Selected foods sources of vitamin A.
The “mcg RAE per serving” refers to the retinol activity equivalent (RAE), which is used to account for the different bioactivities of retinol and provitamin A carotenoids. The “IU per serving” refers to the international units measurement, which is commonly listed on food and supplement labels for vitamin A. The Daily Value (DV) for vitamin A is 5,000 IU for adults and children age 4 and older. This DV was developed by the U.S. Food and Drug Administration (FDA) to help consumers compare the nutrient contents of products within the context of a total diet.
|Food||mcg RAE per serving||IU per serving||Percent DV|
|Sweet potato, baked in skin, 1 whole||1,403||28,058||561|
|Beef liver, pan fried, 3 ounces||6,582||22,175||444|
|Spinach, frozen, boiled, ½ cup||573||11,458||229|
|Carrots, raw, ½ cup||459||9,189||184|
|Pumpkin pie, commercially prepared, 1 piece||488||3,743||249|
|Cantaloupe, raw, ½ cup||135||2,706||54|
|Peppers, sweet, red, raw, ½ cup||117||2,332||47|
|Mangos, raw, 1 whole||112||2,240||45|
|Black-eyed peas (cowpeas), boiled, 1 cup||66||1,305||26|
|Apricots, dried, sulfured, 10 halves||63||1,261||25|
|Broccoli, boiled, ½ cup||60||1,208||24|
|Ice cream, French vanilla, soft serve, 1 cup||278||1,014||20|
|Cheese, ricotta, part skim, 1 cup||263||945||19|
|Tomato juice, canned, ¾ cup||42||821||16|
|Herring, Atlantic, pickled, 3 ounces||219||731||15|
|Milk, fat-free/skim, with added vit A and vit D, 1 cup||149||500||10|
|Baked beans, canned, plain or vegetarian, 1 cup||13||274||5|
|Egg, hard boiled, 1 large||75||260||5|
|Summer squash, all varieties, boiled, ½ cup||10||191||4|
|Salmon, sockeye, cooked, 3 ounces||59||176||4|
|Yogurt, plain, low fat, 1 cup||32||116||2|
|Pistachio nuts, dry roasted, 1 ounce||4||73||1|
|Tuna, light, canned in oil, drained solids, 3 ounces||20||65||1|
|Chicken, breast meat and skin, roasted, ½ breast||5||18||0|
Tolerable upper intake levels for preformed vitamin A.
These upper limits only apply to products from animal sources and supplements whose vitamin A comes entirely from retinol or ester forms, such as retinyl palmitate. However, many dietary supplements (such as multivitamins) consist partly or entirely of beta-carotene or other provitamin A carotenoids. In such cases, the percentage of retinol or retinyl ester in the supplement should be used to determine whether an individual’s vitamin A intake exceeds the upper limit.
|0–12 months||600 mcg RAE (2,000 IU)||600 mcg RAE (2,000 IU)|
|1–3 years||600 mcg RAE (2,000 IU)||600 mcg RAE (2,000 IU)|
|4–8 years||900 mcg RAE (3,000 IU)||900 mcg RAE (3,000 IU)|
|9–13 years||1,700 mcg RAE (5,667 IU)||1,700 mcg RAE (5,667 IU)|
|14–18 years||2,800 mcg RAE (9,333 IU)||2,800 mcg RAE (9,333 IU)|
|19+ years||3,000 mcg RAE (10,000 IU)||3,000 mcg RAE (10,000 IU)|
Recommended dietary allowances, food sources and tolerable upper limits are obtained from the Vitamin A Fact Sheet for Health Professionals (National Institutes of Health).