There are over 600 different carotenoids, for example:
Alpha-Carotene - found in carrots, coriander and green beans
Beta-Carotene - found in apricots, cantaloupe melon and broccoli
Beta-Cryptoxanthin - found in persimmon (Sharon fruit), papaya and tangerines
Capsaicin - found in chilli, sweet red bell and jalapeno peppers
Lycopene - found in tomatoes, guava and watermelon
Lutein - found in turnip, kale and spinach
Zeaxanthin - a strong yellow pigment found in fruits and vegetables
Many have been found to inhibit cancer development but this inhibition is reversible, meaning that stopping a diet rich in carotenoids may allow the cancer to grow again.
Theres a great deal of research into the effects of carotenoids. One way that carotenoids inhibit cancer growth is related to their ability to improve intercellular communication by increasing the production of a protein (connexion 43, C43) which sits between cells. Cancer cells lack the C43 protein, which means they also lack a vital growth control system. A diet rich in carotenoids can help return the situation to normal, especially when combined with selenium a constituent mineral of C43 found in brown rice, fish and Brazil nuts.
Two studies, one from Albert Einstein College of Medicine, New York and the other from Harvard in 2009 showed that eating colourful red, yellow and orange vegetables not only reduced the risk of developing breast cancer, but helped prevent it returning. In both cases the groups eating the carotenoids almost halved their risk. (International Journal of Cancer, 2009 Jun 15; 124(12):2929-37. Cancer Epidemiology; Biomarkers and Prevention. 2009 Feb; 18(2):486-94).
Shhwartz and Shklar at Harvard University studied the ability of carotenoids to inhibit tumour growth in breast, lung, oral and skin tissue. They found a positive response to treatment within 1 to 5 hours.
Stahelin and colleagues from the University of Basel researched the role of a number of antioxidants, including carotene in 3000 men over a period of 15 years. They found that there was an increase in cancers of the stomach and bronchus in subjects with low plasma levels of carotene.
Another example from research concerns vitamin A, mainly created in the body from carotenoids consumed. Known to drive many cancers from breast, to colon, to prostate and even some brain tumours, oestrogen causes its damage by binding to cellular receptor sites. Scientists at the University of Chicago have shown that a metabolite of vitamin A (retenoic acid) can compete with and block this damaging action. Whereas oestrogen causes random and rapid cell growth to occur, the vitamin A was found to ´normalise proceedings´.
(Cancer Watch 2009, CANCERactive)