Unlike vitamin D, calcium, fish oil and other headline-making celebrities of the nutrient world, you may not hear much about vitamin A, but this vital nutrient plays a role in a variety of physiological functions and systems. It’s critical for vision and eye health, enhances the production and activity of white blood cells to support immune function and plays a crucial role in bone health, cell growth and differentiation, organ health and reproductive function.
The term “vitamin A” is a little more complicated than you may think. There are basically two dietary forms:
• Preformed vitamin A, found in animal products like fish, eggs, dairy and meat, doesn’t require conversion and is readily available to and usable by the body.
• Provitamin A carotenoids, found in fruits and vegetables, are converted by the body into retinol, the active form of vitamin A. Beta-carotene is the primary provitamin A carotenoid, though alpha-carotene and beta-cryptoxanthin can also be used. Other carotenoids, like lycopene, lutein and zeaxanthin, aren’t converted into vitamin A (although they have other benefits).
The problem is that the conversion of beta-carotene to vitamin A is highly inefficient, and only a small percentage of beta-carotene actually gets transformed into vitamin A. The process depends on a number of factors, especially healthy gut function and the presence of other nutrients, such as riboflavin, niacin, iron, zinc and adequate dietary protein. Common genetic variations may also significantly impede the body’s ability to convert beta-carotene to vitamin A (see “Should You Take a Supplement?”).
Not to say that’s entirely bad. Beta-carotene that’s not converted into vitamin A circulates through the body and acts as an antioxidant, protecting the cells from free radical damage, reducing inflammation and lowering the risk of cancer, heart disease and other diseases. Additionally, some studies suggest the efficiency of beta-carotene conversion depends in part on the presence of preformed vitamin A – that is, if you eat animal products that are rich in vitamin A, your body may convert less beta-carotene.
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The best approach to ensure you’re getting enough is to include preformed vitamin A in your diet. The top sources are organ meat (especially liver), beef, chicken, turkey, cheese, egg yolks, fish and cod liver oil. If you don’t eat these animal products, make sure you’re getting plenty of beta-carotene in your diet. Focus on orange/red fruits and vegetables, like carrots, sweet potatoes, acorn squash, butternut squash, pumpkin, apricots, cantaloupe and red peppers. Leafy greens like kale, spinach and chard, are also rich in beta-carotene; the orange color is masked by chlorophyll. Be sure to eat them with fat to enhance absorption, and include cooked varieties — some research suggests cooking fruits and vegetables increases their content of beta-carotene. Load up on these carotenoid-packed options:
Try this: Cook finely shredded carrots, onions and garlic in tomato sauce with olive oil then purée for a carotenoid-packed pasta sauce. Thinly slice carrots on the diagonal, toss with melted coconut oil and coarse salt and roast until crispy. Drizzle baby carrots with olive oil, sprinkle with minced rosemary and black pepper and bake until tender.
Try This: Sauté diced sweet potato and onions until tender, stir in black beans, thawed frozen corn, avocado cubes and minced cilantro and serve in taco shells or lettuce cups. Use a spiralizer to make sweet potato noodles, then sauté in olive oil with minced onion, sage leaves and Parmesan cheese.
Try This: Sauté chopped spinach, onion, garam masala and cumin in coconut oil until tender then stir in cream and cubes of paneer cheese and warm through. Purée steamed spinach with avocado and artichoke hearts for a creamy dip. Toss baby spinach leaves with thinly sliced red onions, sautéed mushrooms and sliced hard-boiled egg then drizzle with a warm mustard vinaigrette.
Try This: Toss butternut squash cubes with maple syrup, coconut oil, cinnamon and cayenne pepper and roast until tender. Purée thawed frozen butternut squash with garlic and cream or coconut milk, then warm through for an easy sauce. Halve a butternut squash, roast until tender then stuff with quinoa, chickpeas and minced sautéed greens.
Try This: Toss diced cantaloupe, red pepper, cucumbers, red onion and jalapeño pepper with lime juice and olive oil for a simple salsa. Sprinkle cantaloupe cubes with chile powder and lime then toss with arugula, spinach, fresh basil and olive oil. Purée cantaloupe with coconut milk and fresh mint leaves then freeze in an ice-cream maker for a refreshing sorbet.
Try This: Toss sliced apricots with vanilla extract and honey or agave, top with finely ground almonds and oats and bake until bubbly. Halve fresh apricots, remove pits, add a dollop of crème fraîche or vanilla yogurt and sprinkle with minced basil. Toss quartered apricots with baby spinach leaves, pistachios and crumbled goat cheese and drizzle with vinaigrette.
Try This: Sauté watercress, leeks, garlic and minced red chile peppers in sesame oil then stir in water chestnuts and tamari. Wrap watercress, avocado slices, red bell pepper and hummus in a whole-wheat tortilla. Toss watercress, orange segments and jicama cubes with olive oil and lime juice.
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Should You Take a Supplement?
Beta-carotene is converted by the body into retinol (vitamin A), but certain genetic variations can impact that conversion. The beta-carotene oxygenase 1 (BCMO1) gene is associated with turning beta-carotene into retinol. People with certain variants of the gene may have as much as a 69% decreased conversion of beta-carotene to retinol. It’s not uncommon; in some studies, up to 45% of volunteers were classified as “poor converters,” likely due to genetic variations, and had the ability to form only 9% vitamin A from beta-carotene. Genetic testing can pinpoint BCMO1 gene variations. If you’re a poor converter, taking a supplement that contains preformed vitamin A may be a good choice.
If you’re a vegan or vegetarian, your primary dietary source of vitamin A is fruits and vegetables. Theoretically, a healthy, balanced diet that focuses on whole plants and minimizes processed foods should provide enough beta-carotene. But if your body doesn’t process beta-carotene properly, either because of a genetic variation or other factors, you may not get enough. Some studies suggest vegan women have suboptimal levels of vitamin A. And meat-free diets that are low in protein or zinc can impair beta-carotene conversion efficiency. If you’re a vegetarian but you include eggs, dairy or fish, you’ll probably get enough preformed vitamin A from your diet. If you’re vegan, you may want to consider a vegan-friendly preformed vitamin A supplement.
Other Dietary Factors
Even without genetic variations, the vitamin A activity of beta-carotene is highly variable and surprisingly low. The human intestine has a limited capacity to absorb intact beta-carotene, and some studies show increased consumption of dark green or orange vegetables did not increase vitamin A status. Cooking vegetables increases the availability of carotenoids, as does fat: Studies show that carotenoid-rich vegetables need a certain minimum amount of fat – about 2.4 grams per meal – to ensure their absorption and improve vitamin A status. In general, if your diet consists mostly of raw, uncooked vegetables with little dietary fat, you may not be getting enough vitamin A from dietary beta-carotene, so you may benefit from a preformed vitamin A supplement.
If you do choose a supplement, consider the dose – especially important for preformed vitamin A – since high doses can be toxic, particularly before and during pregnancy. The tolerable upper intake level is 3,000 milligrams per day, unless you’re taking vitamin A under the care of a doctor. That doesn’t apply to beta-carotene; because it’s water-soluble, it doesn’t accumulate in the body — though very high intakes (more than 100,000 IU per day) may turn your skin orange.