miércoles, 15 de agosto de 2012

suplementación??

http://www.ncbi.nlm.nih.gov/pubmed/17922957


 
 


 
British Journal of Nutrition


have been postulated for antioxidant administration both in
health and in disease

6,7.

Reactive oxygen and nitrogen species (RONS) are well
recognised for playing a dual role, both unfavourable and beneficial,
to the cells

8. Overproduction of RONS results in oxidative

stress, a deleterious process that can be an important
mediator of damage to cell structures: lipid, proteins and
DNA

9. In contrast, there is evidence that moderate changes

in RONS concentrations in cells act as signals and may be
beneficial to the cells

4. Although supplementation with antioxidant

vitamins has shown positive anti-atherogenic, anti-carcinogenic
and immunomodulatory effects

10 – 12, the health

benefits of different antioxidants have been the subject of
debate and controversy lately

13.We consider that the contradictory

data can be explained by taking into account several
aspects: the type of antioxidant vitamins used as dietary supplements,
the doses, the antioxidant and the health status in the
supplemented individuals and the duration of the intervention
programmes.


The antioxidant vitamins: dose is important for health
effects


There are several enzyme systems within the body that effectively
scavenge free radicals (see below). In addition, the cell
has many low molecular weight antioxidants. Prominent
amongst these are the main antioxidant vitamins, C and
E. In large doses some vitamins show undesirable side effects
and these tend to increase in severity with increasing dosage.
The likelihood of consuming too much of any vitamin from
food is remote, but overdosing from vitamin supplementation
does occur. At high enough doses some vitamins cause side
effects, such as nausea, diarrhoea, or vomiting

12. When vitamin

side effects emerge, recovery is often achieved by reducing
the dosage. Furthermore, the concentrations of vitamins
that an individual can tolerate vary widely, and appear to be
related to age and state of health.


Vitamin C


Several studies have pointed to an association between vitamin
C intake and chronic diseases. For instance, it was
reported that vitamin C supplementation lowered arterial
blood pressure

14. On the other hand, the role of vitamin C

in cancer prevention remains controversial in spite of a
number of studies that have been conducted over the last 30
years to clarify this point. Nobel laureate Pauling and his colleague
Cameron recommended the use of high doses of
ascorbic acid to cure and prevent the common cold infections
as well as to prevent the onset of cancer

15,16. In a 4-y prospective

study with 30,466 men and women, the risk of mortality
due to all causes for those in the highest quintile of plasma
ascorbate concentration was about one-half that of those in
the lowest quintile of plasma ascorbate concentration

17. Similar

results were also reported for men but not for women

18.

Another study indicated that free-living elderly who consumed
citrus fruits twice a week had adjusted risks of dying that
were half those of elderly who consumed citrus fruit less
than once a week

19. Considerable biochemical and physiological

evidence suggests that ascorbic acid functions as a
free radical scavenger and inhibits the formation of
potentially carcinogenic N-nitroso compounds from nitrates,
including nitrites stomach and thus offers protection against
stomach cancer

20,21. However, there are also studies that do

not show any positive effect after supplementation with
vitamin C

22,23. Clinical studies on cancer patients carried out

at the Mayo Clinic showed no significant differences between
vitamin C and placebo groups with particular regard to survival
time

24. Moreover Lee et al. reported that lipid hydroperoxides

can react with ascorbic acid to form products that could
potentially damage DNA, suggesting that genotoxic metabolites
from lipid hydroperoxides might be formed

25. In this

scenario, ascorbic acid could enhance mutagenesis and risk
of cancer. However the physiological relevance of these
results is yet to be established in

in vivo experiments12.

Finally, it has been reported that tumour cells contain large
amounts of ascorbic acid

26. It has been speculated that high

levels of ascorbic acid in cancer cells may interfere with chemotherapy
or radiation therapy since these therapies induce
cell death by oxidative mechanisms. Thus, ascorbic acid supplementation
might make cancer treatment less effective.
More studies are needed to understand the role of ascorbic
acid in tumour cells and the speculative contraindication of
ascorbic acid for cancer chemotherapy.
Another important aspect that should be taken into account
when supplementing with vitamin C is the possibility that it
acts as a pro-oxidant

in vivo. These pro-oxidative reactions

of vitamin C readily occur

in vitro and recently it has been

demonstrated that they can also have relevance in

in vivo

experiments

27. A high intake of iron along with ascorbic

acid could increase

in vivo lipid peroxidation of LDL and

therefore could increase the risk of atherosclerosis

28. However,

another study demonstrated that in iron overloaded
plasma, ascorbic acid acts as an antioxidant and prevents oxidative
damage to lipids

in vivo29.

Clearly, the possible toxicity of large doses of vitamin C
requires more experimental and clinical studies.


Vitamin E


Numerous epidemiological studies have shown that a high
intake of vitamin E is related to a lower risk of age-related
and chronic diseases. Experimental studies have suggested
substantial health benefits from vitamin E in disease prevention
and therapy.

a-tocopherol, the major form of vitamin E

in the human body, appears to have important health benefits;
these include protection against reproductive diseases (preeclampsia)


30

, age-related eye diseases (cataract, macular

degeneration)

31,32, metabolic disorders (diabetes mellitus)33

and neurodegenerative disorders (Alzheimer’s)

7.

However recent data show unfavourable, rather than beneficial,
effects after supplementation with this antioxidant vitamin.
In 2003, a meta-analysis was performed to assess the
effect of

a-tocopherol and b-carotene, or both, on long-term

cardiovascular mortality and morbidity

34. No positive effect

of high doses of vitamins in different populations was
shown. Due to the lack of data for the efficacy of vitamin E,
the main conclusion derived from this study was that its supplementation
should be discontinued because of its risks.
The authors did not support the routine use of

b-carotene, as

previously shown especially in smokers

35. In other studies

200 IU per day of vitamin E did not have a significant effect


Up-regulation of antioxidant genes by nutrients S37


British Journal of Nutrition


on lowering the incidence of respiratory tract infections in
elderly nursing home residents

36 and 600 IU of the same vitamin,

taken every other day, provided no overall benefit for
major cardiovascular events or cancer in healthy women

37.

Finally, a recent study associated

b-carotene, vitamin A, and

vitamin E supplementation with increased mortality

13.

Thus, the overall conclusion that can be drawn from these
studies is that the general population should not be advised to
take supplements with vitamin E. This, however, does not
mean that vitamin E supplements should not be indicated in
cases of vitamin E deficiency, or prevention of deficiency.
As mentioned previously, Sano

et al. published a seminal

paper in which the efficacy of vitamin E in delaying the physical
deterioration associated with advanced forms of Alzheimer’s
disease was shown

7. Our research group reported that high

doses of vitamin C and E prevented muscle damage associated
with the intake of anti-retroviral drugs which are commonly
used to treat AIDS

11. There is also a report that supplementation

with vitamin E, but not other antioxidants, was effective in reducing
pulmonary viral titres and preventing an influenzamediated
decrease in food intake and weight loss in mice

10.

The fact that other antioxidants were not effective led to the conclusion
that, in addition to its effect as an antioxidant, vitamin E
might be acting via other mechanisms which might not be related
to its antioxidant properties.


The concept of micronutrient malnutrition and deficiency


Micronutrient malnutrition is a term commonly used to refer
to vitamin and mineral nutritional deficiency diseases. Diets
which lack adequate amounts of essential vitamins and minerals
lead to such diseases. Vitamin A deficiency, iron
deficiency anaemia and iodine deficiency disorders are
among the most common forms of micronutrient malnutrition.
Other micronutrients found in food, including vitamins such as
thiamine, niacin, riboflavin, folate, vitamins C and D, and
minerals such as calcium, selenium and zinc can also significantly
affect health when dietary deficiencies exist. As stated,
these deficiencies cause diseases. Well-known human vitamin
deficiencies involve thiamine (beriberi), niacin (pellagra), vitamin
C (scurvy) and vitamin D (rickets). In much of the developed
world, such deficiencies are rare; this is due to (1) an
adequate supply of food; and (2) the addition of vitamins
and minerals, often called fortification, to common foods

38,39.

Micronutrient deficiency is a term used to refer to the situation
where the levels of micronutrients are lower than
requirements, but are high enough to prevent the development
of diseases mentioned.
Ames stated, “our daily intake of the 40 essential micronutrients
is commonly thought to be adequate” but “the optimum
amount of vitamins, minerals, and essential biochemicals is
the amount that maximizes a healthy life span, and is likely
to be higher than the amount needed to prevent acute
deficiency disease”

40.

Micronutrient deficiency diseases


Micronutrients participate in the body in almost all metabolic
and developmental processes

41. Inadequate intakes may result

in chronic metabolic disruption. Several micronutrient
deficiencies are associated with mitochondrial decay,
oxidant leakage and cellular aging

42, which can be responsible

for degenerative disease such as vascular dementia

43, DNA

damage (chromosome breaks) in cultured human cells or

in

vivo

44, or late onset diseases such as cancer.

It is crucial for the understanding of micronutrient deficiency
diseases to distinguish them from micronutrient malnutrition.
The former occurs when the micronutrient intake is lower than
the levels we need for metabolic processes, but are high
enough to prevent the development of the diseases that result
from the latter (e.g. rickets, scurvy, etc.).
Diseases related to micronutrient deficiency, such as degenerative
diseases or cancer, are caused mainly by the chronic
metabolic disruption which is translated into a mitochondrial
decay.
Simple preventive measures like increasing the uptake of
relatively low doses of multivitamin and multimineral supplements
may be instrumental in lowering the incidence of
age-associated degenerative diseases. These ideas are summarised
in the Fig. 1.


Increasing endogenous antioxidant defences versus
increasing the uptake of antioxidant vitamins


The cell possesses a number of extremely powerful mechanisms
to counteract the harmful effects of the inevitable free
radicals which are formed as a consequence of aerobic
metabolism. Of critical importance among these are the enzymatic
systems which catalytically detoxify free radicals and
other reactive oxygen species. For instance, the superoxide
dismutase – glutathione peroxidase system serves to detoxify
superoxide which is formed in the mitochondrial respiratory
chain and to convert it to water via the intermediary formation
of hydrogen peroxide. Other critically important
enzymes exist, for instance catalase which is present in peroxisomes
and which detoxifies hydrogen peroxide very effectively,
converting it to water. Moreover, the importance of
other enzyme systems, such as thioredoxin, glutaredoxin
or sestrins amongst other has been emphasised. From a


Fig. 1.

Summary of the effects of vitamin deficiencies and supplementation.

S38 Jose Vin˜a

et al.

British Journal of Nutrition


nutritional and physiological standpoint, it may be advisable
to increase the expression and activity of these antioxidant
enzyme systems as a way to improve the overall antioxidant
defence capacity of the cells. Thus, we, as well as other laboratories,
have searched for mechanisms which could
increase the activity of critical antioxidant enzymes. In
recent times, we have been considering the observation that
females in many species including humans, live longer than
males

45. We concluded that this is due to the beneficial

effect of oestradiol which is effective at up-regulating the
expression of the genes coding for antioxidant enzymes
such as glutathione peroxidase and superoxide dismutase

45.

Obviously, oestrogens cannot be used as nutritional supplements
because they have many disadvantages, particularly
in males where they are powerfully feminising. Phytoestrogens,
on the other hand, lend themselves as possible candidates
for supplementation to increase the endogenous
antioxidant defences of cells, animals, and eventually
human beings. Phytoestrogens are not feminising (because
they bind quite specifically to oestrogen

b receptors and

the feminising effects are usually associated with the oestrogen
receptor

a activation)46. Moreover, no reports of the carcinogenic

effect of phytoestrogens have been published. They
also have a number of beneficial effects like increasing bone
density, lowering hot flushes associated with menopause and
even partially preventing the incidence of breast cancers

47.

We have found that genistein has beneficial effects in that
it increases the expression and activity of longevity-associated
genes particularly superoxide dismutase and glutathione
peroxidase in a human cell line

48. Moreover, in in vivo experiments,

in which blood pressure was measured in rats using
telemetric methods, administration of phytoestrogens in the
form of a soya-enriched diet lowered blood pressure

49 We

found that this was due to the up-regulation of the expression
of genes such as the endothelial nitric oxide synthase. Therefore,
evidence is gathering that increasing the expression of
antioxidant and other longevity-related genes by the ingestion
(in the form of dietary modifications or of supplementation)
of phytoestrogens or by increased physical activity in the
form of leisurely sport activities that do not cause exhaustion,
increases the expression and activity of longevity-related
genes and may be the ideal ways of improving endogenous
antioxidant defences rather than trying to increase them by
supplementation with antioxidant vitamins.


Conflict of interest statement


The authors work was supported by grants SAF 2004-03 755
and BFU2007-65 803/BFI to J. V., GV06/289 to M. C. G-C
and by grant (ISCIII2006-RED13-027) from the “Red Tema´-
tica de investigacio´n cooperativa en envejecimiento y fragilidad
(RETICEF). Instituto de Salud Carlos III” The authors
have no conflict of interests to declare.


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