Lung cancer is the leading cause of cancer death in the United States, according to MayoClinic.com. Your risk of contracting lung cancer is increased if you smoke or if you are exposed to secondhand smoke. Supplemental use of vitamin A or carotenoid derivatives once believed to help smokers with lung cancer may actually be harmful in high doses. Consult your physician before using vitamin A supplements especially if you are a smoker.
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About Lung Cancer
The two major forms of lung cancer are categorized as small cell, which occurs exclusively in smokers, or non-small cell, which refers to several types of lung cancer that act in a similar manner. According to MayoClinic.com, smoking causes lung cancer by damaging the cells lining your lungs through inhalation of carcinogenic substances from cigarette or tobacco products. Repeated exposure of your lungs to the carcinogens results in cell abnormality and damage. The risk for lung cancer increases the more you smoke and the longer you smoke. Early signs of lung cancer may include persistent cough, shortness of breath and chest pain. Lung cancer can spread to other parts of your body and, in many cases, is fatal.
Lung Cancer and Vitamin A
Vitamin A, an antioxidant, is a historically effective cancer-fighting nutrient. In the 1980s, researchers theorized that use of supplemental vitamin A might reduce the incidence of lung cancer, notes the National Cancer Institute. Large scale clinical trials conducted in Finland and the United States enrolled thousands of smokers, former smokers and people exposed to carcinogenic asbestos to receive daily beta-carotene, vitamin A or placebo. Concluding evidence from both studies found that lung cancer incidence increased by 16 to 28 percent in participants taking beta-carotene or vitamin A supplements. Post-trial follow ups further found that the overall death rate of supplement takers remained higher than study participants who had taken placebo.
Vitamin A Function
The group of compounds that convert to vitamin A in your body are referred to generally as retinoids and carotenoids. Vitamin A from animal-based foods such as dairy is absorbed in your body as retinol, and vitamin A from plant-based foods such as produce is in the form of a carotenoid that is made into retinol once digested. Vitamin A plays an important role in cellular, reproductive and visual health and has antioxidant properties. Antioxidants are protective molecules that neutralize harmful free radical molecules from damaging cells.
Vitamin A Intake and Sources
The daily recommended intake of vitamin A for adults is 700 to 900 micrograms. Supplemental vitamin commonly comes from beta-carotene, retinyl palmitate or retinyl acetate and should not exceed the tolerable upper limit of 3,000 IU, notes the Linus Pauling Institute. Natural sources of vitamin A include carrots, broccoli, spinach, cantaloupe, squash and fortified milk. If you smoke, vitamin A from food sources is not associated with toxicity if you consume too much. However, if you choose to take supplements, consult your physician first for dosing recommendations.