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Journal of Pakistan Association of Dermatologists. 2020; 30(3): 412-417.
412
Address for correspondence
Dr. Adawiyah Jamil,
Department of Medicine,
University Kebangsaan Malaysia Medical Center,
Bandar Tun Razak, Cheras, 56000 Kuala Lumpur,
Malaysia.
PH: +060391456074
Email: adda_jamil@yahoo.com
Original Article
Photoprotection and skin whitening effect of dietary
soy milk in healthy young female adults
Introduction
Ultraviolet (UV) radiation from the sun has
multiple potentially detrimental effects on the
skin including skin cancers, photodermatoses,
photoaggravated diseases, photodamage and
photoaging. Photoprotective measures are
required for prevention and treatment of these
conditions. Midday sun avoidance, seeking
shade, topical sunscreens, protective clothing
and headgears are recommended sun protection
measures.1 However, sun-protective practices
are still largely inadequate2-4 despite sun safety
education due to the inconvenience of these
measures.3 A safe and effective oral sunscreen
would be ideal.
Soy (Glycemic max) is a legume that is high in
protein and fiber. Soy milk contains 3.5%
protein, 2.0% fat, 0.5% ash, 2.9%
carbohydrates5 and a high amount of isoflavone
that scavenger free radicals released by UV
exposure to prevent skin aging and protect
against UV induced skin damage.6 Genistein,
daidzein and glycitein are 3 major types of
isoflavone, soy milk contain mostly genistein. In
addition to UV protection, genistein lightens the
skin as it interferes with melanin synthesis
pathway by inhibiting melanin production.7-9
H Haron, A Jamil*, NA Awang Besar
Nutritional Sciences Programme, School of Healthcare Sciences, Faculty of Health Sciences
Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia.
* Department of Medicine, University Kebangsaan Malaysia Medical Center, Bandar Tun Razak,
Cheras, Kuala Lumpur, Malaysia.
Abstract
Background Topical soy formulations improve signs of aging and protects against ultraviolet light.
We aimed to determine photoprotective and whitening effects of oral soy.
Methods Healthy volunteers drank commercial soy milk containing 20mg isoflavones twice daily
for 8 weeks, and avoided consumption of isoflavone-rich food, sunscreen and lightening products.
Phototest and skin colour measurement was performed at baseline and at the end of study.
Results Thirty healthy females aged 21(19-22) years with Fitzpatrick skin type III and IV
participated. Soy milk significantly increased whiteness at the cheek and gluteal regions. Minimal
erythema dose (MED) to UVA increased in 60% subjects, MED to UVB increased in 87%.
Significant reduction in UVB induced erythema was observed with all UVB doses, UVA induced
erythema decreased with higher doses.
Conclusion Short term regular consumption of soymilk showed photoprotection and skin whitening
effects.
Key words
Soy milk, photoprotection, whitening, minimal erythema dose, ultraviolet light.
Journal of Pakistan Association of Dermatologists. 2020; 30(3): 412-417.
413
Oral genistein has been shown to protect mice’s
skin from UV10 but its effect on human’s skin
has not been investigated. We conducted a study
to determine the effect of dietary soy milk in UV
protection and skin whitening in healthy young
females.
Methods
This was a prospective, open label interventional
cohort study performed over 8 weeks at the
Faculty of Health Science, Universiti
Kebangsaan Malaysia (UKM). Subjects were
recruited by convenience sampling among
students of the faculty. Inclusion criteria were
females aged 18-35 years old with no chronic
disease such as hypertension and diabetes,
individuals who like soy products and able to
fulfil the study requirements. Exclusion criteria
were known allergy to soy products,
photosensitivity or having skin that is sensitive
to sunlight, routine excessive exposure to the
sun (e.g. athletes), on any medicine or
supplements, and smokers.
Informed consent was obtained from volunteers
who fulfilled the inclusion and exclusion
criteria. Subjects completed a food frequent
questionnaire (FFQ)11 to determine their usual
dietary intake of soy products in the last 1
month. The FFQ consisted of 24 types of foods,
portions were determined using standard
measurements from Atlas of Food Exchange and
Portion Size.12 Subjects then underwent a 2
weeks washout period where they were asked to
avoid soy products, other photoprotective foods
and use of sunscreens. Baseline phototest and
skin colour assessments were then performed.
Subjects were instructed to consume 250mls of a
commercial soy milk in the morning with
breakfast (between 7-9am) and at noon with
lunch (between 12noon to 2pm) and to continue
avoiding other soy products, photoprotective
foods and use of sunscreens for the next 6
weeks. At the end of the study, phototest and
skin colour assessments were repeated.
The isofalvone dose required for its
photoprotective effect was estimated based on
an animal study performed by Wei et al.10 About
40mg of isoflavone per day was given to our
subjects by consuming a commercial soy milk
containing 6g of protein/ 250mls. The estimation
of isoflavone content in soy milk was based on
protein calculation proposed by Nagata et al.13
Photoprotective effects were measured by
phototest with UVB and UVA to determine the
degree of erythema induced on the skin by
multiple doses of UV. The minimal erythema
dose (MED) which is the lowest dose of UV
required to induce erythema were also
documented. Lower values of the degree of
erythema and higher MED indicates
photoprotective effects. The degree of erythema
was objectively measured using a mexameter.
Skin color was assessed at the right cheek to
represent a sun exposed area and the right
gluteal region to represent a covered area.
Chromameter measured the lightness or
whiteness of the skin while mexameter
measured melanin or darkness.
Calculated sample size was 30, based on results
from Heinrich et al.13 and adjusted for 10%
missing data. Ethical approval was obtained
from the UKM Research Ethics Committee
(UKMREC).
Results
Thirty healthy female subjects with median age
of 21 (19-22) years and Fitzpatrick skin type III
and IV participated in the study. The average
soy products intake based on FFQ was
66.66±111.50 g/day, while the average intake of
isoflavone was 22.82±39.40 mg/day. The most
common types of dietary soy products and the
amount consumed were commercial soy milk,
Journal of Pakistan Association of Dermatologists. 2020; 30(3): 412-417.
414
Table 1 The effect of soy milk on skin whiteness and darkness
Site
Whiteness (N=30)
Darkness (N=30)
Week 0
Median (IQR)
Week 6
Median (IQR)
p value
Week 0
Median (IQR)
Week 6
Median (Q1,Q3)
p value
Face
30.00
(2.89)
30.80
(3.61)
0.01
42.73
(3.78)
40.41
(4.63)
0.01
Gluteal
28.07
(8.52)
29.93
(8.22)
0.00
44.81
(9.63)
43.53
(9.72)
0.00
Figure 1 Type and amount of dietary soy products
Figure 2 Source and amount of dietary isoflavones
soy bean sprout, soft tofu pudding and fried tofu.
(Figure 1). Soy milk was the most consumed
soy product (30.20 g/day) and the highest source
of dietary isoflavone (7.01mg/day). The source
and amount of dietary isoflavones are
summarised in Figure 2.
Table 2 and 3 show changes in UVA and UVB
induced erythema on the skin before and after
soy milk consumption. Erythema was reduced
with all doses of UVA and UVB. The reductions
were significant with higher doses UVA at 4.5
and 5.0 J/cm2. Erythema with all doses of UVB
ranging from 32 to 130 mJ/cm2 were
significantly reduced.
1.73
2.26
2.62
3.98
5.77
6.1
6.32
30.2
0 5 10 15 20 25 30 35
Sambal Jawa
Sambal tempe
Japanese tofu
Fried tempe
Fried tofu
Soft tofu pudding
Soybean sprouts
Soy milk
Intake of soy products (g/day)
Type of soy products
0.74
1.65
1.89
2.17
2.48
3.58
7.01
012345678
Samabal Jawa
Soft tofu pudding
Sambal tempe
Soybean sprouts
Fried tofu
Fried tempe
Soy milk
Intake of isoflavones mg/day
Source of isoflavones
Journal of Pakistan Association of Dermatologists. 2020; 30(3): 412-417.
415
Table 2 Erythema induced by phototest with multiple
doses of UVA before and after soy milk consumption
UVA
dose
(J/cm2)
Erythema N=30
Week 0
Median (IQR)
Week 6
Median (IQR)
p
value
2.0
14.10(2.65)
13.43 (2.61)
0.09
2.8
14.99 (3.35)
14.15 ( 3.20)
0.05
3.5
14.88 (3.81)
14.35 (3.71)
0.74
4.3
14.77 (3.43)
14.30 (2.34)
0.02
5.0
15.91 (3.74)
14.07 (2.18)
0.00
Table 3 Erythema induced by phototest with multiple
doses of UVB before and after soy milk consumption
UVB
dose
(mJ/cm2)
Erythema (N=30)
Week 0
Median (IQR)
Week 6
Median (IQR)
p
value
32
14.92(3.81)
14.41(3.76)
0.03
44
15.45(3.15)
14.40(2.24)
0.03
56
15.66(3.33)
14.47(3.30)
0.05
68
15.87(3.42)
15.03(2.32)
0.01
80
16.51(3.68)
14.99(3.09)
0.00
52
15.81(4.71)
14.42(3.44)
0.01
72
16.41(4.92)
15.43(2.40)
0.04
91
16.85(4.22)
15.63(3.18)
0.00
111
17.55(3.47)
15.20(2.75)
0.00
130
17.63(3.54)
16.19(2.27)
0.00
The MED to UVA increased in 18(60%) of
subjects, while the MED to UVB increased in 26
(87%). Skin color measurements on the cheek
and gluteal region showed a significant increase
in whitening and reduction in darkness at both
sun exposed and covered areas. Whiteness of
face increased from 30.00 to 30.80 unit, p=0.01
while at the gluteal region, increment from 28.07
to 29.93 unit, (p=0.00) was observed (Table 1).
Synchronously, the measurement of skin
darkness/ melanin on the face decreased from
42.73 to 40.41 unit, p=0.0. The gluteal region
showed a decline in the melanin measurement
from 44.81 to 43.53 unit, p= 0.00 (Table 2).
There were no adverse effects reported
throughout the study.
Discussion
The amount of soy isoflavone intake in our
study population was slightly lower to that
reported in Japan,15,16 Hong Kong, Singapore,15
China17 and Korea.18 Asian diets in general are
richer in isoflavones compared to Western diet
and the sources of isoflavones differ as well.19-21
Isoflvones are mainly derived from peas, beans,
coffee, tea, nuts and grains in the west while soy
is the major source of isoflavones in Asia.19 Soy
milk was by far the most favoured product by
our subjects compared to soy prepared by
fermentation or traditional recipes. Most reports
on isoflavone intake in Asia were on middle
aged population that consumed more
concentrated forms of soy like tofu, paste and
curd,16,22,23 this explains the lower value seen in
our younger population that consumed soy
mainly as a drink.
Genistein and daidzein in soy have both
antioxidant and anti- inflammatory effect against
UV induced cell damage that results in skin
aging and predisposes to skin cancer.10,24,25
Genistein inhibits mitogen-activated protein
kinases in keratinocytes and fibroblasts which is
responsible for stimulation of matrix
metalloproteinases to produce collagenase,
gelatinase and stromelysin-1. These enzymes
break down collagen, elastin and other
components of the dermal matrix that results in
skin aging.26-28 Soybean trypsin inhibitor (STI)
and Bowman-Birk protease inhibitor (BBI) are
soy proteins that inhibit activation of
keratinocytes’ protease-activated receptor 2
(PAR-2).8,9 Activation of this receptor will
initiate transfer of melanosomes from
melanocytes to keratinocytes by phagocytosis.
In addition, soy isoflavones are potent inhibitors
of tyrosinase, the crucial enzyme in melanin
synthesis.29 Lightening of skin color occurs due
to reduced melanin production and reduction in
the number of melanosomes in keratinocytes.
Topical soy formulations has been shown to
reduce pigmentation, improve signs of aging like
wrinkling and elasticity of the skin and protects
against UVA and UVB.7,10,27,30,31 Oral
Journal of Pakistan Association of Dermatologists. 2020; 30(3): 412-417.
416
formulations produces the same pigmentary and
aging effects.10,30 The benefit of oral forms of
soy genistein and daidzein against UVA and
UVB have been demonstrated in vivo and in
vitro in mice and human skin cell
culture.10,24,25,30 It has not been documented in
humans to the best of our knowledge. Our
results revealed the photoprotective effect of
dietary soy against UV in healthy young adults.
Better protection was achieved against UVB as
significant reduction in UVB induced erythema
was observed from low doses. Protection against
UVA was observed only at higher doses. Skin
whitening was another effect seen at both sun
exposed and covered areas. A limitation of our
study is, quantity of isoflavone in soy milk was
estimated based on its protein content, it was not
objectively measured. However, our results
illustrate soy isoflavone‘s potential as oral
sunscreen with added benefits of skin lightening
and reduction in skin aging. The optimal dose of
isoflavone or genistein and daidzein, and a
detailed side effect profile in long term use need
to be further determined. In conclusion, dietary
soy milk is protective against UVA and UVB
and whitens the skin. Its potential as oral
sunscreen and skin whitening agent needs to be
further evaluated.
Acknowledgements
The authors would like to thank Pn. Julianah
Ramli and Pn. Nur Arifah Muhd Rafiee for their
technical assistance in performing the
phototests.
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