Did your mother ever threaten that you will need glasses if you did not eat your carrots? Well, although you may have eaten your carrots, her motivational tactics were questionable. If you were following a generally balanced diet, then those extra carrots had no affect on your vision. The connection does make sense, though. Carrots contain beta-carotene, which your body converts into vitamin A, and vitamin A is important for healthy eyesight. However, only a small amount is needed to maintain good vision. Foods that are high in beta-carotene and vitamin A will only impact your vision if your body is deficient in vitamin A.
Standard, well-balanced diets in the developed world generally contain a sufficient amount of vitamin A, and eating more carrots will not make a big enough difference to affect eyesight. The Third National Health and Nutrition Examination Survey (NHANES III), conducted by the National Center for Health Statistics from 1988-1994, found that most Americans take in the amount of vitamin A recommended by the Institute of Medicine (IOM).
The Recommended Dietary Allowances (RDAs) for vitamin A are as follows:
More recent data collected from 1999-2000 found that the average adult continues to get enough vitamin A, taking in around 3300 IU per day.
Healthful, well-balanced diets contain a variety of sources of vitamin A, examples include:
Dark-colored fruits and vegetables (like carrots) contain provitamin A carotenoids, which are converted to vitamin A in the body. However, when your body has enough vitamin A, this conversion slows down. No benefits or risks are associated with eating extra carrots, although over-consuming beta-carotene can turn your skin orange or yellow (carotemia). This is not considered bad for your health.
People with vitamin A deficiency, which is common in developing countries, are at risk for night blindness and can benefit from eating foods rich in vitamin A (like carrots). Studies have shown that eating carrots and other foods containing beta-carotene and vitamin A can improve vision for people with vitamin A deficiency and subsequently poor vision.
A recent study investigated the effect of providing nightblind, pregnant Nepali women with vitamin A, some in supplement form and others in foods like carrots or liver. The subjects were compared to Nepali women who could see normally at night and had no deficiency in vitamin A. After receiving treatment six days per week for six weeks, nearly all of the nightblind women reported full recovery, their vision approaching the level of the non-nightblind pregnant women.
Recent studies in developed countries have shown that older adults, who are at risk for age-related macular degeneration (AMD), may benefit from a diet rich in antioxidants including beta-carotene. A study conducted in Rotterdam, the Netherlands from 1990-2004 found that antioxidant-rich foods may slow the onset of macular degeneration. According to the study, consuming high amounts of beta-carotene, vitamins C and E, and zinc was associated with a substantially reduced risk of AMD in elderly patients.
However, it is important to note that the high levels of beta-carotene that produced such results were obtained from vitamin and mineral supplements, and it would be very difficult to reach the same level of intake by eating lots of carrots. Also, there is no evidence that excessive carrot consumption prevents macular degeneration or other diseases affecting vision at any age. Again, consuming excessive beta-carotene may result in carotemia.
During World War II, the British Royal Air Force invented the myth tying carrots to clear, sharp vision as a way to explain the sudden increase in Nazi bombers being shot down. A disinformation campaign spread the rumor that British fighter pilots were eating carrots to improve their vision, when in reality the British had a new radar system they wanted to keep secret from Germany. The story caught on though, and it remains popular to this day. Although there is a grain of truth to the claim, most people will not experience positive changes in their vision from eating carrots unless they have a vitamin A deficiency.
Dietary supplement fact sheet: vitamin A and carotenoids. Office of Dietary Supplements, National Institutes of Health website. Available at:http://ods.od.nih.gov/factsheets/vitamina.asp. Accessed June 8, 2006.
Haskell MJ, Pandey P, Graham JM, et al. Recovery from impaired dark adaptation in nightblind pregnant Nepali women who receive small daily doses of vitamin A as amaranth leaves, carrots, goat liver, vitamin A-fortified rice, or retinyl palmitate.Am J Clin Nutr. 2005 Feb;81(2):461-471.
Kruszelnicki, KS. Great moments in science–carrots and night vision. Available at:http://www.abc.net.au/science/k2/moments/s1392430.htm. Accessed June 8, 2006.
Myths about Vision and Eyeglasses. Health and Age website. Available at:http://www.healthandage.com/Home/%21gm%3D20%21gsq%3Dmyths%21gid2=3028. Accessed June 7, 2006.
Takita Y, Ichimiya M, Hamamoto Y, et al. A case of carotenemia associated with ingestion of nutrient supplements.J Dermatol. 2006 Feb;33(2):132-4.
There's hope for people with age-related macular degeneration. American Academy of Ophthalmology website. Available at:http://www.aao.org/news/release/20060310.cfm. Accessed June 7, 2006.
van Leeuwen R, Boekhoorn S, Vingerling JR, et al. Dietary intake of antioxidants and risk of age-related macular degeneration.JAMA. 2005;294(24):3101-3107.
Image Credit: Nucleus Communications, Inc.