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 South and Central
America the reliance on corn as their main carbohydrate resulted in Vitamin B6
deficiency instigating a disease called pellagra. The manifestation of rashes,
weakness and malabsorption devastated large communities until it was discovered
that adding limes to corn enabled the vitamin B6 to be absorbed hence the
propensity now for limes with tortilla and other corn dishes to this day. In the
Far East, the reliance on rice only as their stable carbohydrate source, low in
thiamine, caused vitamin B1 deficiency resulting in nerve damage and a disease
known as beri beri. Asians particularly women and children emigrating to the UK
in the 60’s had a high incidence of bone diseases such as osteomalacia and
rickets due to vitamin D and calcium deficiency brought on by the lack of
sunshine and low dairy diet.
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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