Transcript Antioxidants

Antioxidants
Presented by
Janice Hermann, PhD, RD/LD
OCES Adult and Older Adult Nutrition Specialist
Free Radicals
 Body uses oxygen in metabolic reactions.
 Sometimes oxygen reacts with body
compounds and forms unstable molecules
called free radicals.
 Free radicals can also be formed by
environmental factors:
 Ultraviolet radiation
 Air pollution
 Tobacco smoke.
Free Radicals
 A free radical has one or more unpaired
electrons.
 An electron without a partner is unstable and
very reactive.
 To gain stability, a free radical attacks another
stable but vulnerable compound and steals an
electron.
Free Radicals
 After losing an electron, the previously stable
molecule becomes a free radical.
 It then it attacks another molecule stealing an
electron.
 This process results in an electron-stealing
chain reaction with one free radical producing
another free radical.
Free Radicals
 Sometimes free radical attacks can be
beneficial.
 For example, the immune system uses free
radicals as an “oxidative burst” to destroy
disease causing viruses and bacteria.
Free Radicals and Disease
 However, free radical attacks can also cause
extensive damage.
 Free radicals especially damage
polyunsaturated fatty acids in lipoproteins
and in cell membranes.
 Free radicals also damage cell proteins
(altering functions) and DNA (creating
mutations).
Free Radicals and Disease
 If free radical damage becomes extensive,
health problems can develop.
 Oxidative stress has been identified as a
causative factor in:
 Cognitive performance
 Aging process
 Development of diseases such as cancer, arthritis,
cataracts, and heart disease
Defending Against Free Radicals
 The body has several lines of defense against
free radical damage.
 The body’s natural immune system tries to
control the free radical damage, but these
systems are not 100 percent efficient.
 This system become less efficient with age and
free radical damage accumulates.
Defending Against Free Radicals
 The immune system utilizes enzymes to
disable the damaging effect of free radicals.
 The enzymes depends on selenium, copper,
manganese, and zinc.
 If the diet provides inadequate amounts of
these minerals, this weakens this line of
defense.
Defending Against Free Radicals
 The body also uses antioxidants to protect
the body against oxidative damage.
 Antioxidants can end the chain reaction of
forming new free radicals by donating one of
their own electrons.
 When antioxidants donate an electron they
do not become a free radical because they
are stable in either form.
Defending Against Free Radicals
 Two antioxidant vitamins the body uses are in
defense of free radicals are vitamin E and
vitamin C.
 Vitamin E protects body lipids (cell
membranes and lipoproteins) by stopping the
free-radical chain reaction.
Defending Against Free Radicals
 Vitamin C protects watery components in the
body (fluid in the blood) against free radical
damage.
 Vitamin C also is especially good at stopping
free radicals air pollution and cigarette
smoke.
 In addition, vitamin C may also restore
oxidized vitamin E to its active state.
Defending Against Free Radicals
 Dietary antioxidants also non-nutrients
including some phytochemicals.
Defending Against Free Radicals
 Together, vitamin and mineral nutrients and
phytochemicals with antioxidant activity
protect against certain diseases and decrease
free radical damage by:
 Limiting free-radical formation
 Destroying free radicals or their precursors
 Stimulating antioxidant enzyme activity
 Repairing oxidative damage
 Stimulating repair enzyme activity
Defending Against Cancer
 Cancers occur when cellular DNA is damage
causing mutations.
 Sometimes this damage is caused by free-radical
attacks.
 Antioxidants may reduce cancer risk by
protecting DNA from oxidative damage.
 Many studies report lower cancer rates
among people who consume abundant fruits
and vegetables rich in antioxidants.
Defending Against Cancer
 Diets rich in vitamin C correlated with lower
cancer rates, especially cancer of the mouth,
larynx, esophagus, and stomach.
 Such correlations reflect the benefit of
consuming a diet rich in fruits and vegetables
and low in fat, but it does not necessarily
support taking vitamin C supplements to treat
or prevent cancer.
Defending Against Cancer
 Protective effect of vitamin E against cancer
is less consistent than that for vitamin C.
However, people with low vitamin E blood
levels E have higher rates of certain types of
cancer.
 Several studies also report a cancer
protective effect of fruits and vegetables rich
in beta-carotene and the other carotenoids.
Defending Against Heart Disease
 High LDL cholesterol is a major risk factor for
cardiovascular disease.
 One way LDL cholesterol increases the risk of
cardiovascular disease is that free radicals in
the arteries oxidize LDL cholesterol.
 Oxidized LDL cholesterol accelerates the
formation of artery-clogging plaques.
Defending Against Heart Disease
 Free radicals also oxidize polyunsaturated
fatty acids in cell membranes, initiating
additional changes in artery walls which
decrease blood flow.
 Oxidative damage in artery walls is increased
by a diet high in saturated fat or cigarette
smoke.
Defending Against Heart Disease
 On the other hand, diets high in fruits and
vegetables, especially in combination with
low saturated fat, increase antioxidant action
against LDL cholesterol oxidation which can
help decreases the development of
atherosclerosis.
Defending Against Heart Disease
 Antioxidants, especially vitamin E, may
protect against the development of
cardiovascular disease.
 Epidemiological studies have reported that
people who consume diets rich in vitamin E
have lower rates of death from cardiovascular
disease.
Defending Against Heart Disease
 Some studies also suggest that vitamin C
protects against LDL cholesterol oxidation,
raises HDL, lowers total cholesterol, and
improves blood pressure.
 Vitamin C may also decrease free radical
oxidation in the artery wall that typically
follows a high-fat meal.
Foods or Supplements
 As previously mentioned in the process of
stopping free radicals, antioxidants
themselves become oxidized.
 To some extent, antioxidants can be
regenerated, but still, losses occur.
Foods or Supplements
 To maintain free radical defenses, people
need to replenish dietary antioxidants on a
regular basis.
 This raises the question is antioxidants be
replenish from foods or supplements?
Foods or Supplements
 In making recommendations for antioxidant
nutrients, the DRI Committee considered
whether studies supported substantially
higher antioxidant nutrient intakes to help
protect against chronic diseases.
 The DRI Committee raised the DRI
recommendations for vitamins C and E, but
did not support taking vitamin supplements
over eating a healthy diet.
Foods or Supplements
 Isolated supplements are limited.
 Vitamin E supplements, for example, usually
contain alpha-tocopherol, but foods provide
an assortment of tocopherols among other
nutrients, many of which provide protection
against free-radical damage.
Foods or Supplements
 One factor is research is lacking to determine
exactly what component, or combination of
components, in foods may beneficial.
 Foods – especially fruits and vegetables – not
only supply antioxidants, but also fiber and
many other vitamins, minerals, and
phytochemicals.
Foods or Supplements
 Isolated supplements are limited.
 Vitamin E supplements, for example, usually
contain alpha-tocopherol, but foods provide
an assortment of tocopherols among other
nutrients, many of which protect against free
radical damage.
Foods or Supplements
 Furthermore, much more research is needed
to define optimal and dangerous levels of
intake.
 Antioxidants behave differently at various
levels of intake.
Foods or Supplements
 At physiological levels typical of a healthy
diet, act as antioxidants, but at
pharmacological doses typical of
supplements, act as pro-oxidants, stimulating
the production of free radicals.
 This is especially likely in the presence of
other antioxidants or minerals such as iron.
Foods or Supplements
 Demonstrated in two studies investigating
whether beta-carotene supplementation
would reduce the incidence of lung cancer
among smokers.
 Studies found the incidence of lung cancer
was higher among smokers receiving betacarotene supplements than those taking a
placebo, resulting in an early end to the
studies.
Foods or Supplements
 Until optimum intake levels of these nutrients
can be determined, the risks of supplement
use remains unclear.
 The best way to add antioxidants to the diet is
to eat generous servings of fruits and
vegetables daily.
Foods or Supplements
 In addition, it’s important not to try to single
out one particular food for a specific nutrient,
antioxidant, or phytochemcial.
 Recommendations are to consume a wide
variety of fruits and vegetables in generous
amounts daily to get the variety of important
compounds these foods have to offer.
References
 Wadsworth, 2005. Thomson Wadsworth Publishers.
 Understanding Normal and Clinical Nutrition, 7th
edition by Sharon R Rolfes, Kathryn Pinna & Ellie
Whitney, 2006. Thomson Wadsworth Publishers
 International Food Information Council, Functional
Foods Fact Sheet: Antioxidants, 2006. www.ific.org,
accessed January 2007.