INTRODUCTION
- Acne is the most prevalent skin condition, affecting to some
degree 85% of the population aged 11 to 30 years.
- It is not a life-threatening condition; however, it lasts
for years and can cause physical and emotional scars
- Several studies found that overall knowledge about the
causes, natural course, and therapy was very low, not only among patients but
also among final year medical students and even among family physicians and
nurses
- In an attempt to advise patients knowledgeably on the
subject of nutrition, one is inundated with and confused by the mountains of
epidemiologic studies that appear in the scientific, pseudoscientific, and non-scientific
literature.
- Unfortunately, convincing trials are lacking, because it
turns out that no meta-analyses, randomized controlled clinical studies, or
well-designed scientific trials have followed evidence-based guidelines for
providing solid proof in dealing with this issue
ECOLOGIC STUDIES
- An ecologic study is an observational study on risk factors
and disease prevalence in which different population groups are compared to
identify associations.
- Because all data are aggregate at the group level,
relationships at the individual level cannot be empirically determined. This type
of study provides weak empiric evidence
From ecologic studies,
- A difference in the prevalence of acne between non-Westernized and
fully modernized societies has been noted, and diet has been suspected to be
the reason.
i) Acne was absent in the Inuit (Eskimo) population when they were still living and eating in
their traditional manner. The prevalence of acne became similar to that in
Western societies after their acculturation.
ii) Surveys of disease in some rural African villages in Kenya, Zambia, and the Bantu in South Africa
report far less acne than is found in the descendants of people in these areas
who now live in the United Kingdom or the United States
iii) A study of schoolchildren from Purus Valley, a rural region in Brazil found: of 9955 children aged
6 to 16 years, only 2.7% had acne vulgaris
iv) Two non-Westernized isolated population: the Kitavan Islanders of Papua New Guinea,
and the Ache hunter-gatherers of Paraguay,
had diet that includes mainly traditional foods that are locally cultivated. An
analysis of 1200 Kitavan individuals, including 300 aged 15 to 25 years, and
115 Ache individuals including 15 aged 15 to 25, found not a single case of acne of any grade.
[The authors suggested that the absence of acne in
non-Westernized societies is attributable to environmental factors, mainly
local diets, which have a substantially lower glycemic index than the Western
diet. Even they admit that an alternative explanation of the low prevalence of
acne in these non-Westernized populations is that of genetic susceptibility to
acne, especially given that the people in these isolated regions live in
close-knit and closed communities.]
- In epidemiology it is called the “ecological fallacy,” meaning that even if such a link is supported
by biologically plausible hypotheses of mechanism of causation, it does not provide proof of a causal
relationship, because the individual diet of the individuals who develop
acne is not known and confounders cannot be assessed.
- It can even be postulated for the purpose of discussion
that the dietary restrictions that Western adolescents with acne adopt in
managing their condition are trivial
compared with the differences between their diets and those of hunter-gatherers
ACNE AND DAIRY
PRODUCTS
- A 1949 study reported 1925 patients who kept food diaries
and found that milk was the most common food implicated in acne flares.
- A more recent report also supporting an association
between milk consumption and acne was based on the Nurses Health Study II
cohort
- Intake of milk
during adolescence was associated with history of teenage acne. This
association was more marked for skim milk than for other forms of milk,
suggesting that the finding is unlikely
to be caused by the fat content of milk.
Biological
Plausibility
- The authors hypothesize
that this association may be caused by
the presence of hormones and bioactive molecules in milk. Acne in teenagers
was correlated with hormonal activity
- Milk contains placenta-derived progesterone and other dihydrotestosterone
(DHT) precursors, including 5α-pregnanedione and 5α-androstanedione. These
compounds are only a few enzymatic steps away from DHT, the main acne stimulator, and the enzymes required to mediate
the change are present in the human pilosebaceous unit
- Milk also contains a multitude of growth-stimulating
hormones
- The most likely of
all candidates for costimulation with the steroid hormones of pilosebaceous
function and dysfunction is insulin like growth factor-1 (IGF-1), which is
present in ordinary milk. IGF-1 stimulates the synthesis of androgens in the
ovary, adrenals, and testicles. Insulin
itself and, even more so, IGF-1 have been demonstrated to stimulate hair follicle
growth and sebocyte growth
- Accordingly, the blood
level of IGF-1 in prepubertal, pubertal, adolescent, and early adult humans
resembles accurately the prevalence curve of acne in this population. Human and bovine IGF-1 share the same amino
acid sequences, and several milk proteins protect IGF-1 from digestion in the
gut. Therefore, it is likely that IGF-1 may mediate some of the effects of
comedogenic factors, such as androgens, growth hormone, and glucocorticoids
- An alternative hypothesis explaining the association between
milk and acne suggested that the iodine
content of milk might also have an effect in the development of acne.
- However, whether iodine in any concentration causes true
acne is debatable. Acneiform eruption can be triggered by halides, and iodine
was also recognized as causing an acneiform eruption. The comedo, as the
initial lesion in acne, is not part of this eruption
Limitation
- Although the biologic explanation seems plausible, the study
is not innocent from pitfalls in methodology
- First, the validity of the data collected by distantly recalled eating habits and vaguely
defined disease is questionable.
- The study was cross-sectional:
a causal relationship cannot be determined and a temporal correlation cannot be
established.
- Thus, the direction of the association between the alleged
cause and the effect cannot be defined. As a consequence, a reverse causation cannot be rule out.
- Therefore, the association between acne and milk found in
this study should be treated with caution
So, can milk cause acne?
- The association between dietary dairy intake and the
pathogenesis of acne is slim.
ACNE, CHOCOLATE
AND FATTY FOODS
- Chocolate, oily or fatty foods, and foods with high sugar content
have been repeatedly nominated as causing or exacerbating acne. Is there
convincing evidence for such a link?
- The effect of dietary
fat content on insulin resistance has been a subject of controversy
- In human studies, although some studies indicate a link between
dietary fat intake and insulin resistance, most show no such relationship.
- The general consensus among the experts today is that the
available valid scientific data are
insufficient to prove such a correlation
- It is proposed that high glycemic indexes lead to hyperinsulinemia and a resulting cascade
of endocrine consequences, including increased androgens, increased IGF-1, and
altered retinoid signaling pathways, that mediate acne
- Several animal studies demonstrated an inverse correlation
between a high glycemic index, hyperinsulinemia, and insulin resistance, but few
studies on humans have yielded inconsistent results or failed to show such an effect
- Most experts have taken the position that not enough valid scientific data are
available to support such a link.
- Because it is generally accepted that the severity of acne
is correlated with facial sebum secretion, it has been hypothesized that foods high in fat or carbohydrates may exacerbate
acne by production of more comedogenic sebum—by increasing blood lipid levels
or by producing sebum that is less fluid, and thence greater obstruction of pilosebaceous
follicles—thus setting the stage for follicle rupture and secondary
inflammatory changes
- Several human studies have also demonstrated that diet may
change the amount and composition of excreted sebum, that is, an increase in lipid secretion when either excess
carbohydrates or fats were given.
- An important study showed that sebaceous glands can and do
use fatty acids from the bloodstream for the synthesis of sebum.
So, can chocolate or
oily foods cause or exacerbate acne?
- Two studies of acne and chocolate have considerable methodologic
shortcomings
- In a methodologically stronger trial, a single-blind, placebo-controlled,
crossover study performed in American hospital acne clinic attendees and male
prisoners found no effect of chocolate on acne or on sebum production or composition
- A small study of 16 patients with acne and 13 matched controls
found no difference in sugar consumption between the 2 groups, although
patients with seborrheic dermatitis had higher levels of sugar consumption.
- No effect was established between acne and chocolate, dairy
products, shellfish, or fatty foods in another study
- A study with several methodologic limitations, as
explained before, found that high-fat and high-carbohydrate foods such as
sweets, pizza, and French fries did not cause acne
CONCLUSIONS
- At present, we are
bereft of reliable answers based on scientific evidence.
- We hope that the day when we will be able to knowledgeably
advise our acne patients on the role of nutrition in relation to acne etiology
is not too far away.
[Upcoming: The role of MNT in Acne]
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