Sources of Vitamin A
Good food sources of vitamin A include cod liver oil, eggs, butter, whole milk, sweet potato, carrot (raw), cantaloupe, spinach, and squash. On the meat front, liver has the highest amount of retinal, a form of vitamin A. Approximately 70% of vitamin-A intake is derived from dietary retinal and the rest comes from carotenoids in plants, which are converted to vitamin A in our bodies. About 50% of the vitamin A needed in our diets is derived from carotenoids.
There are supplements, too, including beta-carotene and preformed vitamin A (retinol). Many multivitamins in the U.S. provide 1,500 mcg (5,000 IU) of vitamin A, a value substantially higher than the current recommended levels. Since retinal intake of 5,000 IU a day has been linked with an increased risk of osteoporosis in the elderly, there is a trend for the vitamin manufacturers to reduce the retinal content to half the original (750 mcg or 2,500 IU). Talk to your doctor to see if you need to supplement.
This is an essential vitamin and safe if taken at proper doses. In rare cases, an overdose can lead to hypervitaminosis A, a condition associated with long-term ingestion of vitamin A over 10 times the recommended level. Certain people, including the elderly and alcoholics, are more sensitive to vitamin-A toxicity, which can cause dizziness, dry skin, nausea, loss of appetite, itchy skin, headache, and fatigue. In worst cases, overdose can cause liver failure, hemorrhage, and even coma.
For this reason, U.S. officials set the tolerable upper level of vitamin A intake for adults at 3,000 mcg or 10,000 IU a day of preformed vitamin A. In other words, don’t ever take more than this a day.
Several studies suggest that taking 1,500 mcg a day (5,000 IU) over the long-term can raise the risk of bone fracture in older adults. Many people exceed this daily amount all the time through multivitamins and such fortified foods as cereal. I suggest that you choose a multivitamin that contains 2,500 IU of vitamin A or 5,000 IU only if 50% of it comes from beta-carotene. (It should say on the bottle.)
For expecting mothers, vitamin A should be monitored closely, as it’s linked with birth defects. Pregnant women should cut down to 770 mcg (2,600 IU) a day, while breastfeeding women should get 1,300 mcg (4,300 IU) a day.
Finally, vitamin A does have some drug interactions. Speak to your doctor if you take any of the following: acetaminophen; anticonvulsants; methyldopa; any existing vitamin-A products; warfarin; tetracycline; neomycin; orlistat; mineral oil; oral contraceptives; and bile acid sequestrants.
Here are the three previous articles in this series: