This document discusses two antioxidants - vitamin C and lutein. Vitamin C is found naturally in fruits and vegetables and helps prevent oxidative damage associated with diseases. The average vitamin C intake in the US meets recommended levels. Lutein is a carotenoid found in green leafy vegetables, fruits, and eggs that is absorbed with fat. Clinical trials found that lutein supplements enhanced macular pigment and improved vision in older adults with early macular degeneration. Another study found lutein and DHA supplements improved cognitive test performance in seniors. Due to these benefits for vision and cognition, lutein supplements or diets high in lutein may be beneficial for older adults.

1. Antioxidant Research: Vitamin C and Lutein
NHM454 Section 901: Experimental & Functional Food
Due date: November 8, 2013
Kayoko Zahn

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Introduction
Oxidative stress is caused by excessively produced reactive oxygen species
(ROS) in the body due to various stressors such as UV radiation, pollutants and
smoking.1 Abnormal ROS activity is known to be associated with heart disease and
cardiovascular disease (CVD).2 The human body fights against ROS through an
antioxidant defense system that uses both endogenous and exogenous antioxidants.1
They inhibit oxidation of cellular targets by neutralizing free radicals.1 Endogenous
antioxidants including enzymatic and non-enzymatic antioxidants are synthesized in the
body.1,2 Exogenous antioxidants are dietary antioxidants commonly found in fruits,
vegetables and grains.1,2 They include vitamins and minerals that are essential
nutrients, and a variety of phytochemicals that are considered non-essential nutrients
such as flavonoids, phenolic acids, and certain carotenoids.1,2
In this report, the functions of antioxidants are reviewed by featuring vitamin C
and the phytochemical lutein. First, vitamin C is discussed including statistical data on
consumption in the US, its functions for homeostasis and disease conditions,
differences of bioavailability, and influence on shelf-life and storage. Secondly, lutein, a
type of carotenoid, possessing antioxidant properties3 is discussed regarding its
functions in the human body. Finally, two primary intervention research articles are
highlighted in which the therapeutic value of lutein is evaluated.
The Science Behind Vitamin C
Vitamin C, also known as ascorbic acid, is a water soluble vitamin naturally found
in fruits and vegetables, especially citrus fruits.4,5 Vitamin C is an essential nutrient
because, unlike most animals, humans lack the enzyme which synthesizes ascorbic

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acid.4 Ascorbic acid, the reduced form of the vitamin existing in the body, works as an
effective antioxidant by neutralizing toxic free radicals due to its potent reducing
activity.4,6 Excessive ROS due to low serum vitamin C levels leads to oxidative damage
which is associated with degenerative diseases such as cancer and CVD.4,6 Vitamin C
is an essential nutrient for collagen, hormone, amino acid and carnitine biosynthesis
and for dopamine conversion in the nervous system.4,6 Historically, the observation of
scurvy led to the discovery of vitamin C in 1932.4,6 The symptoms of scurvy include
bleeding gums, follicular hyperkeratosis, joint effusions, and ultimately sudden death.6.7
Scurvy is a severe vitamin C deficiency with the plasma ascorbic concentration being
less than 12 µM while a normal healthy level is 70 µM.4,6,7 Bioavailability of ascorbic
acid depends on both absorption from the intestines and excretion from the kidneys.4
When 30-180 mg of dietary vitamin C is ingested, the rate of absorption is about 7090 %.6 A randomized bioavailability study of vitamin C in young male adults indicated
that bioavailability of vitamin C derived from kiwifruit was not significantly different from
synthetic vitamin C. However this contradicted the results of animal studies.5 The
serum ascorbate level increased after the intervention of 50 mg vitamin C for 6 weeks in
the kiwifruit and vitamin C tablet groups from 23 to 46 µM and 24 to 51 µM
respectively.5
The current recommended daily allowances (RDAs) for vitamin C are 75 mg and
90mg daily for adult females and males respectively.6,7,8 The tolerable upper intake
level (UL) for vitamin C is 2,000 mg per day in adults.6,8,9 This UL was set due to the
adverse effects of osmotic diarrhea and gastrointestinal disturbances which may be
caused by high dosages.6,9 Vitamin C is thought to have low toxicity based on its

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chemical properties as a water-soluble vitamin and the physiological mechanism
controlling its concentration in the body.6,9 According to the 2009-2010 National Health
and Nutrition Examination Survey (NHANES) data, the average vitamin C intake of 82
mg for females and 96 mg for males in adults mostly met the RDAs.10
Besides its role as a vitamin, ascorbic acid is often added to commercial food
products as a preservative.11 A study of ascorbic acid degradation using an ultraviolet
(UV) light food processing model was conducted to evaluate UV effects on vitamin C
content and shelf-life in ascorbic acid fortified apple juice.12 The result indicated that
ascorbic acid concentration decreased with longer UV treatment and higher pH. Malic
acid and fructose also affected the rate of degradation. The concentration of ascorbic
acid also decreased during prolonged storage at high temperatures.12
The Science behind Lutein
Lutein and zeaxanthin are xanthophylls known to have strong antioxidant
properties similar to β-carotene.13,14 Zeaxanthin is an isomer of lutein.14 The major
difference of lutein and zeaxanthin compared to other carotenoids is the presence of
hydroxyl groups at both sides of the long carbon chain backbone.13 The nine double
bonds in the structure are responsible for the property of blue light absorbance at 450
nm which makes the color of lutein yellow or orange.13
The dietary sources of lutein and zeaxanthin include green leafy vegetables,
bright colored fruits, and eggs.3,13,15 The solubility of lutein increases with fat containing
diets. The bioavailability of lutein is more sensitive to a diet rich in fat than other
carotenoids such as β-carotene.13 Lutein in plants is esterified while lutein in eggs
exists as a free alcohol form. Lutein supplements derived from plants are saponified to

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remove esters.13 The bioavailability of lutein depends on the esterification and the fat
contents of the diet which affects the formation of micelles for uptake in the
gastrointestinal tract.13 A recent study showed the absorption of free lutein was
improved with esterified lutein supplements.13 The RDA for lutein has not been set due
to insufficient evidence.16 According to the data from 2009-2010 NHANES, the average
daily intakes of lutein and zeaxanthin from food are about 1.6 mg for adult females and
1.5 mg for males in the US.10 One study showed a protective association against agerelated macular degeneration (AMD) at an intake level of 6 mg of lutein per day while
another study showed marked deficiency of these xanthophylls at an intake level of 1 to
2 mg per day.13 There is no data indicating any adverse effects of lutein and zeaxanthin
intake.14 No side-effects were observed at a lutein supplementation level of 26 mg lutein
per day in a study which showed a protective effect against lung-cancer.14
Lutein and zeaxanthin are the only carotenoids found in the human retina and
they are precursors to macular pigment (MP). They are therefore hypothesized to be
beneficial for eye health and protective against AMD.3,13,14,16 Lutein and zeaxanthin's
influence in improving cognitive function in older adults is another area of research due
to their localization as the dominant carotenoids accumulated in human brain and their
protective nature.3,15 Following are two recent studies about the effects of lutein and
zeaxanthin on retinal function and cognitive function.
Highlighting Primary Intervention Research on Lutein - Article 117
The effect of lutein supplementation in patients with early stage AMD was
investigated by measuring macular pigment optical density (MPOD) and visual acuity
(VA). A randomized, double-blind, placebo-controlled clinical trial was conducted in

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Manchester, UK and in Maastricht, the Netherlands over 12 months. Inclusion criteria
for study participants were males and females from 50 to 80 years of age with AMD
grade 0 to 4 in one eye, best correlated visual acuity (BCVA) of LogMar higher than 0.5,
and minimal cataract. Criteria of exclusion were ophthalmic disorders, optic atrophy,
pigmentary abnormarities, history of glaucoma, and recent lutein supplementation.17
Out of 84 patients randomly assigned to take either lutein (L) (10 mg esterified
lutein) or placebo (P) supplement, 73 patients, 37 (L: n=17, P: n=20) in Manchester and
36 (L: n=19, P: n=17) in Maastricht, completed the trial. Blood serum lutein, BCVA,
fundus photographs and MPOD were measured before treatment and in the 4th month,
8th month, and 12th month of treatment.17
No statistical differences were found before treatment, but the MPOD data
indicated substantial effects at the 8 and 12th month in the L group. No significant
change was observed in the P group. MPOD level for the L group increased from 0.38
± 0.19 to 0.53 ± 0.22 which was about a 40 % increase over the baseline. In the L
group, substantial increase of serum lutein level (average increase 300%) was
observed in both locations. The VA data showed nonsignificant improvement in L group
from 0.1 ± 0.17 to 0.09 ±0.14 in VA while statistically significant deterioration was seen
in P group from 0.05 ± 0.13 to 0.09 ± 0.13 at the 12th month period from the baseline.
The mean change in VA increased by + 0.01 logMAR for L group and decreased by 0.04 logMar for P group.17 This was the first study which showed lutein
supplementation for one year had functional and MPOD effects and clearly suggests
lutein supplementation is beneficial in enhancing MP.17
Highlighting Primary Intervention Research on Lutein - Article 218

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The effects of supplementing with lutein or with docosahexaenoic acid (DHA) and
lutein on cognitive function in older women were investigated in a randomized, doubleblind, placebo-controlled trial conducted in Boston, MA with a duration of 4 months. The
inclusion criteria for study participants were healthy female non-smokers of ages 60 to
80. Exclusion criteria were lactose intolerance, diseases in liver, kidney, pancreas, or
blood, diabetes, high cholesterol, alcoholism, or current medications and supplements
that might block fat-soluble vitamin uptake.18
Forty nine women out of 57 recruits were randomly selected to receive lutein
(n=11, 12 mg/day), DHA (n=14, 800 mg/day), lutein and DHA (n=14), and placebo
(n=10). Subjects were asked to take supplements with a fat-containing energy drink to
control lutein uptake. More than 97 % compliance was confirmed by measuring serum
lutein and DHA. Several cognitive tests were conducted at the beginning and the end of
the trial. Outcomes were adjusted by age and education in the statistical analysis.18
In the Verbal Fluency test, all supplement groups named items significantly better
than the baseline. In the Shopping List Memory test, lutein plus DHA supplement group
learned significantly faster than the other groups. Correlation analysis suggests that the
only co-variable associated with Verbal fluency after supplementation was age.
Younger subjects recalled more names after supplementations of lutein, DHA and the
combination. Serum DHA level was correlated with the Verbal Fluency and Shopping
List scores. On the other hand, serum lutein level and cognitive tests were not
consistent. The lutein group showed poorer performance in the Shopping List test after
supplementation. This result may be related to the fact that this group had the highest
baseline. No relationship between serum lutein level and Verbal Fluency scores was

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found.18 This was the first study of the effects of lutein supplementation in combination
with DHA in an older population. It showed positive effects on several cognitive tests.
Further investigation is required to confirm the benefits of lutein supplementation in
cognitive functions.18
Lay Audience Summary
Dietary antioxidants such as vitamin C have important roles protecting against oxidative
stress in the body. Vitamin C, a water soluble vitamin, naturally found in fruits and
vegetables, prevents oxidative damage which is associated with cancer and CVD. The
average vitamin C intake in the US meets the recommended daily allowances (RDA) of
75 mg for female and 90 mg for male in adults. The closely related carotenoids, lutein
and zeaxanthin, are another type of antioxidant, naturally found in green leafy
vegetables, bright colored fruits, and eggs. The RDA for lutein has not been set. The
average dietary lutein intake of adults in the US is about 1.5-1.6 mg. The absorption of
lutein is affected by the fat content in the diet. Lutein and zeaxanthin are converted to
macular pigment (MP) in the human retina. A 12 month clinical trial carried out in older
populations with daily lutein supplementation of 10 mg, suggested beneficial effects of
lutein for enhancing MP and protective effects against age-related macular
degeneration. Lutein and zeaxanthin are known to be accumulated in the human brain.
A 4 month study of the effects of daily supplementing with 12 mg of lutein or combining
with 800 mg of docosahexaenoic acid (DHA) on cognitive function in a population of
seniors showed positive effects on several cognitive tests. Due to the clinical effects on
vision and cognitive functions in older patients, treatment with lutein as a dietary
supplement or diets rich in lutein may be beneficial for older patients.

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References
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4. Li Y, Schellhorn HE. New developments and novel therapeutic perspectives for
vitamin C. J Nutr. 2007;137(10):2171-84.
5. Carr AC, Bozonet SM, Pullar JM, Simcock JW, Vissers MC. A Randomized SteadyState Bioavailability Study of Synthetic versus Natural (Kiwifruit-Derived) Vitamin C.
Nutrients. 2013;5(9):3684-95.
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/DRIs/5_Summary%20Table%20Tables%201-4.pdf. Accessed October 9, 2013.
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10. What We Eat in America, NHANES 2009-2010 Data: individuals 2 years and over
(excluding pregnant and/or lactating females and breast-fed children), day 1 food and
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http://www.ars.usda.gov/SP2UserFiles/Place/12355000/pdf/0910/Table_37_SUP_GEN
_09.pdf. Accessed October 20, 2013.
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12. Tikekar RV, Anantheswaran RC, LaBorde LF. Ascorbic acid degradation in a model
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light. Prog Retin Eye Res. 2012;31(4):303-15.
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Opt. 2004;24(4):339-49.
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Johnson EJ. A possible role for lutein and zeaxanthin in cognitive function in the elderly.
Am J Clin Nutr. 2012;96(5):1161S-5S.
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reference intakes. Nutr Rev. 2008;66(8):459-64.
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Lutein supplementation over a one-year period in early AMD might have a mild
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