β-Carotene and physiology
β-Carotene and cancer
An article on the American Cancer Society says that The Cancer Research Campaign has called for warning labels on β-carotene supplements to caution smokers that such supplements may increase the risk of lung cancer.The New England Journal of Medicine published an article in 1994 about a trial which examined the relationship between daily supplementation of β-carotene and vitamin E (α-tocopherol) and the incidence of lung cancer. The study was done using supplements and researchers were aware of the epidemiological correlation between carotenoid-rich fruits and vegetables and lower lung cancer rates. The research concluded that no reduction in lung cancer was found in the participants using these supplements, and furthermore, these supplements may, in fact, have harmful effects. The Journal of the National Cancer Institute and The New England Journal of Medicine published articles in 1996 about a trial with a goal to determine if vitamin A (in the form of retinyl palmitate) and β-carotene (at about 30 mg/day, which is 10 times the Reference Daily Intake) supplements had any beneficial effects to prevent cancer. The results indicated an increased risk of lung and prostate cancers for the participants who consumed the β-carotene supplement and who had lung irritation from smoking or asbestos exposure, causing the trial to be stopped early.A review of all randomized controlled trials in the scientific literature by the Cochrane Collaboration published in JAMA in 2007 found that synthetic β-carotene increased mortality by 1-8 % (Relative Risk 1.05, 95% confidence interval 1.01–1.08).
In Australia, organic β-carotene is produced by Aquacarotene Limited from dried marine algae Dunaliella salina grown in harvesting ponds situated in Karratha, Western Australia. BASF Australia is also producing β-carotene from microalgae grown in two sites in Australia that are the worlds largest algae farms. In Portugal, the industrial biotechnology company Biotrend is producing natural all-trans-β-carotene from a non-genetically-modified bacteria of the genus Sphingomonas isolated from soil. Carotenes are also found in palm oil, corn, and in the milk of dairy cows, causing cows milk to be light yellow, depending on the feed of the cattle, and the amount of fat in the milk (high-fat milks, such as those produced by Guernsey cows, tend to be yellower because their fat content causes them to contain more carotene). Carotenes are also found in some species of termites, where they apparently have been picked up from the diet of the insects. Synthesis
There are currently two commonly used methods of total synthesis of β-carotene. The first was developed by BASF and is based on the Wittig reaction with Wittig himself as patent holder:
The second is a Grignard reaction, elaborated by Hoffman-La Roche from the original synthesis of Inhoffen et al. They are both symmetrical; the BASF synthesis is C20 + C20, and the Hoffman-La Roche synthesis is C19 + C2 + C19. Nomenclature
Carotenes are carotenoids containing no oxygen. Carotenoids containing some oxygen are known as xanthophylls. The two ends of the β-carotene molecule are structurally identical, and are called β-rings.