Vitamins and cancer
These are chemicals which are essential to the normal biochemical function of our body’s metabolism – they cannot be made internally and without them we’ll get ill so they have to be ingested regularly in the diet. The most notable historical example of vitamin deficiency was scurvy among sailors which was corrected by British sailors by eating vitamin C within limes (earning their nick name -limies).
In modern society with the wide choices of food available to us, overt vitamin deficiencies are unlikely. These historical example do however serve as good lesson that it is important to varying our food sources – too much reliance of one source could lead to sub clinical deficiencies which although unlikely to manifest itself as the full blown syndrome may impair the bodies ability to fight cancer. The most important vitamins implicated in the cancer process, described in the last chapter, include vitamins A, C, D, E but it would wise to aim for a diet which provided adequate amounts of all the vitamins as well as the essential fatty acids and minerals;
Vitamin A is a fat-soluble essential vitamin found in fish and dairy food in the isoform retinol. It can also be ingested in fruits and vegetables that contain carotenoid provitamins such as beta-carotene which is then metabolised to vitamin A. Prostate cancer cells grown in the laboratory have demonstrated an increased apoptosis (programmed cell death) and reduced proliferation (growth) when exposed to synthetic retinoids such as fenretinide. Likewise in genetically susceptible mice fenretinide reduced the incidence of prostate cancer by 49%. However, in a subsequent prospective study involving 10,472 U.S. men, no reduction in prostate cancer incidence has yet been demonstrated, although there have only been 93 events so far in the 5 years follow up period. Evidence of a benefit in humans with an adequate diet has therefore not been established.
Sources and tips fish and dairy food in the form of retinol. It can also be ingested in fruits and vegetables such as carrots, spinach, cabbage that contains the carotenoid pro-vitamin beta-carotene which is then metabolised to vitamin A.
Vitamin C is involved, in the mechanism, which enables DNA to "sense" the damage done by free radicals by integrating with the iron imbedded in DNA. This process facilitates DNA repair and is therefore and important factor in immune surveillance. This is an important factor in stage of cancer development which takes place in the seconds between the DNA damage to the subsequent mutation, gene rearrangement and then cancer. This protection is needed every minute of every day as according to estimates, each cell in the body can be expected to suffer approximately 100,000 potentially DNA-damaging events per day so the a healthy DNA repair system is imperative. Vitamin C has also been shown to protect the intracellular component cell from toxic products such as hydrogen peroxide. This is thought to be via a mechanism which prevents inhibition of gap-junction intercellular communication (GJIC). Inhibition of GJIC is related to carcinogenesis and tumour promotion. Convincing experiments in humans in relation to cancer have not been done but, except in very large does, vitamin C should to be harmful. Whether taking higher doses than necessary adds any anti-cancer benefit remains unproven
Sources and tips – a water soluble vitamin found in citrus fruits including limes, oranges, and lemons as well as numerous other fruits and berries such as apples, bananas, cranberries, cherries etc. Improvements in food logistics have also ensured that the availability of fruits from around the world has never been so good. Exotic varieties often have very high vitamin C levels such as kiwi, pineapple, mango, papaya and star fruit. As the fruit ripens the vitamin C content increases so don’t be put off by a few soft bits! Fruit juices are a great way to increase your fruit intake and a healthy alternative to most fizzy sugary drinks. If you’re thirsty on a hot summers day consider a freshly squeezed orange juice mixed with water and ice. One lemon squeezed into a pitcher with a spoon of honey topped up with sparkling water makes healthy lemonade for the children. These natural drinks, although a bit more effort, are healthy, cheap, tasty and a great alternative to the sugary, chemical rich drinks found on the majority of cans and bottles on our shelves. Ideally fruit juices should also be drunk fresh. After squeezing, the juice changes its chemical composition quickly becoming more acidic and loosing its vitamin and other nutrient content. The juices within cartons have been heavily processed and often have to have the vitamin C re-added to keep the levels up. Most plastic bottled “freshly squeezed” juices and smoothies and been pasteurised to prolong their shelf life. Although, there is little evidence that this is harmful, heating and cooling a food to extreme temperatures is not particularly natural - it also affects the taste. If possible look for unpasteurised juices or better still eat the real fruit, make your own smoothies or squeeze them yourself.
On a separate point, people often say – “I can’t eat fruit because I have indigestion or heart burn”. Although it’s true that initially fruit can result in a little irritation, in vulnerable individuals, it is not the root cause of the problem and in the long term fruit will improve the health of the stomach and oesophagus (gullet). The underlying cause is usually an unhealthy balance of fat, meats and sugar which the stomach has to work harder to digest – i.e. produce more hydrochloric acids. To make matters worse, sufferers often turn to antacids for immediate relief. The stomach then senses a more alkaline environment and responds by producing yet more acid, perpetuating the problem. On the other hand, consumption of mildly acidic fruit sends signals to the stomach lining to produce less of its own acid. After a while, with perseverance, eating fruit and other less gastric irritating foods will therefore reduce the acid levels and improve health of the gastric lining and prevent indigestion.
Vitamin D is converted to the active metabolite calciferol in the kidney. to Cancer cells exposed to calciferol in the laboratory has been shown to help key factors in cancer progression, namely; reduce proliferation, promote differentiation, inhibit invasion, prevent loss of adhesion and promote apoptosis. It has also be shown to interact with the androgen signalling pathway in animals inhibiting the production of factors which stimulate new blood vessels growing into cancers – stopping them growing. (angiogenesis). Clinical studies of calciferol had to be abandoned however because it dangerously increased serum calcium. Scientists have now developed a new vitamin D analogues which are hoped to have the anticancer properties but without the risk of a raised calcium and these are currently being investigated in a large ongoing multicentre study.
Sources and tips an oily vitamin which is converted to the active metabolite calciferol in the kidney. Present in nuts, fish, fish oils such as cod liver oil, fresh vegetables, grains and cereals. Large quantities are generated by sunlight on our skin – sensible regular sun exposure is good for vitamin D levels although it is important not to burn or over do it. (see tips for sensible sun exposure in the appendix).
Vitamin E has eight naturally occurring isoforms. The tocopherols have been thought to be linked to the cancer process mainly via an antioxidant effect. Tocopherols have also been shown to prevent less aggressive tumours changing to to a more aggressive type (differentiation). In humans a number of large trials have provided an excellent insight into the relationship between vitamin E and cancer. The Alpha-Tocopherol Beta-Carotene cancer prevention study trial (ATBC), involved 29,133 male smokers taking Vitamin E (alpha-tocopherol) and Vitamin A (Beta-carotene) or a placebo. After several years follow up, the treatment group had a statistically significant reduction in the incidence of prostate cancer. At last a positive supplement to may be saying to yourself, but before you applaud too loudly there was a problem. The incidence of lung cancer the main end point was higher in the treatment group than the placebo. This beneficial effect on prostate cancer is probably genuine because it was supported by a further large trial involving male health workers called the Health Professional Follow up Study (HPFS). In this study vitamin E intake was also associated with decreased risk of prostate cancer but only in smokers but not overall. The relationship between smokers, the risk of prostate cancer and vitamin E was then investigated in the Cancer Prevention II (CPII) Nutrition Cohort study. As well a detailed dietary history, this study also measured blood levels of vitamin E. It showed that blood vitamin E was lower in smokers and a correlation low blood vitamin E levels and higher incidence of prostate cancer. This correlation was particularly high with the isoform of vitamin E callede gamma-tocopherol which is the main Vitamin E found in health foods as opposed to the alpha-tocopherol found in man made supplements. A further trial involving 5000 patients with diabetes or cardiovascular disease, this time in women (The womens Health Study). Supplementation with alpha tocopherol demonstrated no reduction in cancer, and the incidence of heart disease was slightly worse. Likewise, in the ATBC study cerebral haemorrhage risk was also higher in smokers with hypertension who took alpha-tocopherol.
The ongoing USA National Cancer Institute sponsored, double blind, randomised SELECT study comparing selenium and vitamin E supplementation against placebo will provide data on completion in 2013.
Vitamin E has eight naturally occurring isoforms called the the tocopherols. Smokers have lower levels and have most to gain by ensuring adequate vitamin E levels. The various forms of vitamin E can be found in fresh fruit, raw and calciferous vegetables, grains, oily fish, nuts and salads.
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