Alcohol consumption affects risk of cataracts
Critique (28.09.2013) 021 25
October 2010
Kanthan GL, Mitchell P, Burlutsky G,
Wang JJ. Alcohol Consumption and the Long-Term Incidence of Cataract and
Cataract Surgery: The Blue Mountains Eye Study. Am J Ophthalmol
2010;150:434440.
Authors Abstract
(http://www.bu.edu/alcohol-forum/alcohol-consumption-affects-risk-of-cataracts/)
(www.karmayog.org)
? PURPOSE: To assess whether
alcohol consumption is associated with the long-term incidence of cataract or
cataract surgery.
? DESIGN: Population-based
prospective cohort study.
? METHODS: A total of 3,654
persons aged 49+ years were examined at baseline and 2,564 were re-examined
after 5 and/or 10 years. Lens photographs were taken at each visit and
assessed using the Wisconsin Cataract Grading System by masked graders.
An interviewer-administered questionnaire was used to collect information
on alcohol consumption.
? RESULTS: No significant
associations were observed between alcohol consumption and long-term risk of
nuclear, cortical, and posterior subcapsular cataract. However, after
adjusting for age, gender, smoking, diabetes, myopia, socioeconomic status, and
steroid use, total alcohol consumption of over 2 standard drinks per day was
associated with a significantly increased likelihood of cataract surgery, when
compared to total daily alcohol consumption of 1 to 2 standard drinks (adjusted
odds ratio [OR] 2.10, 95% confidence interval [CI] 1.16-3.81). Abstinence
from alcohol was also associated with increased likelihood of cataract surgery
when compared to a total alcohol consumption of 1 to 2 standard drinks per day
(adjusted OR 2.36, 95% CI 1.254.46).
? CONCLUSION: A U-shaped
association of alcohol consumption with the long-term risk of cataract surgery
was found in this older cohort: moderate consumption was associated with 50%
lower cataract surgery incidence, compared either to abstinence or heavy
alcohol consumption.
Forum Comments
This is an interesting paper that
deals with a common medical condition that will continue to be of great
importance with the ageing of the population.
Background: Few longitudinal studies have dealt with cataracts,
with the Beaver Dam Eye Study (BDES)1 the only one prior to the
present one that has been population based. BDES found little
relationship between alcohol and cataracts, although there was some evidence
for a U-shaped curve with posterior subcapsular cataracts.
Among other cohort studies, the
Nurses Health Study2 found little evidence of an effect of alcohol
intake on the risk of surgery for cataracts. Their data are compatible
with a slight decrease in risk of total cataracts with light drinking (up to
14.9 g/day) and an increased risk for certain types of cataract with greater
amounts of alcohol. An earlier report from the Physicians Health Study3
reported no significant effect of alcohol, although there was a trend towards
increased risk of certain types of cataracts with greater alcohol intake.
Comments on the Present Study: The strengths include the analyses being based on a
population-based cohort with excellent recruitment and good retention of
subjects, and repeated eye examinations with excellent ascertainment of
cataracts. The investigators had blinded assessments of lens photographs
for the objective diagnosis of cataracts. Weaknesses that limit the information
presented relate to the choice of the category with 1-2 drinks/day as the
referent group, as there were very few subjects reporting consumption at this
level. (For example, there were only 4 subjects with posterior
subcapsular cataracts in the referent group consuming wine and 8 in the
referent group for beer.) The paper does include in the text the
associations between alcohol and cataract surgery using nondrinkers as the
referent group, and state that persons reporting moderate alcohol consumption
(1-2 drinks/day) had a significantly reduced incidence of cataract surgery (OR
0.47, 95% CI 0.26-0.85), but data are not presented for the lighter
drinkers.
One would assume that data on the development
of cataracts would be more objective and informative than on the occurrence of
cataract surgery, as the latter may be related to many other socio-economic
factors. (On the other hand, the associations generally changed very
little when the age-gender-adjusted rates are compared with the fully adjusted models
that included socio-economic status.)
It is unfortunate that the authors
chose to not include in their paper the results of multivariable-adjusted
analyses for many categories, since the dose-response pattern is often more
informative than the statistical significance of any one cell. In other
words, if odds ratios of cataracts are lower in both the non-drinkers and the
heavier drinkers than among the moderate drinkers, it would suggest a
U-shaped association. The conclusions of the authors are apparently
based exclusively on statistical results and tend to not describe the pattern
of effect for each beverage and total alcohol
Of the results in the categories of
alcohol intake reported, there was a clear pattern suggesting a U-shaped
relation only for cortical cataracts for beer and red wine intake, and
suggestions of an increase in risk with spirits intake. Also, the shape
of the relation suggested a potential increase in risk of posterior subcapsular
cataracts for beer and spirits. For cataract surgery, there was a
step-wise decrease (not statistically significant) for red wine going from no
alcohol to >2 drinks/day, but there was a suggestion of a U-shaped curve for
other beverages and total alcohol. (The total alcohol category is difficult
to interpret due to different patterns of effect with different beverages).
Potential mechanisms of an effect of
alcohol on risk of cataracts:
Potential mechanisms for both beneficial and adverse effects of alcohol on
cataract formation have been identified, making the effects of alcohol, and
especially wine, on the risk of developing cataracts biologically
plausible. As stated by the authors, Alcohol has been shown to disrupt
calcium homeostasis in the lens, augment processes such as membrane damage, alter
protein-protein interactions, and produce pro-oxidant molecules when
metabolized in the liver.
Forum members state that cataracts
in diabetics can be due to an oxidative process; polyphenols in wine and
certain other beverages may play a role in decreasing risk of cataracts.
There are a number of studies showing that cataract and macular degeneration
appear when the diet is low in antioxidants. Vitamin C (highly
concentrated in the crystalline lens) seems to have a protective effect4,5.
Some antioxidants have been explored with this disease, from melatonin (able to
reduce oxidative markers), to vitamin C or quercetin, that have been found to
be protective with enzymatic markers in crystalline lens. Possibly the
phenolics and metabolites (from wine) could play a role in the economy of
vitamin C in the crystalline lens or act directly as protective compounds
against the oxidative process, as has been demonstrated by Yamakoshi et al6.
Red wine procyanidins and their antioxidative metabolites can prevent the
progression of cataract formation by their antioxidative action against NADPH
oxidase and other oxidative enzymes. The larger molecular procyanidins in
wine might contribute to this anti-cataract activity.
Pathophysiological mechanisms of
cataract formation may also include deficient glutathione levels contributing
to a faulty antioxidant defense system within the lens of the eye.
Moreover, diabetic cataracts are mainly caused by an elevation of polyols
within the lens of the eye catalyzed by the enzyme aldose reductase.
Flavonoids, quercetin and its derivatives for example, are potent inhibitors of
aldose reductase.
However, one should be aware that
from a drug-delivery perspective, ocular bioavailability depends on the
physicochemical and biopharmaceutical characteristics of the selected compound
and more importantly the route of administration. Indeed, in order to
trigger an effect, bioactive compounds should be found at the site of the
problem (i.e., the eye) and therefore need to cross the blood brain
barrier. This is possible as several line of evidence place some
polyphenols and their metabolite within the brain.
It is also important to stress that
upon consumption, bioactives will undergo metabolism by phase 1 and 2 enzymes,
therefore decreasing their antioxidant potential. Thus, it is more likely
that the bioactive compounds may induce xeno-hormetic actions leading to
increases in GSH though the Keap1-Nrf2-ARE pathway, for example. Another
possible mechanism is the direct inhibition of some enzymes responsible for
increased levels of free radicals such as the NADPH oxidase (act as
apocynin-like inhibitors) or the decrease of the plasma glucose level as
observed in a study dealing with the impact of astaxanthin on cataract in
salmon7.
Increased risk of cataracts with
heavy alcohol consumption:
One Forum member emphasizes that excessive alcohol intake may be associated
with an increase in some types of cataracts. He states that in his
practice in Scandinavia, about 25% of patients younger than age 65 years who
present with cataract are found to be heavy alcohol consumers. He adds:
It has been my experience that if the opacities are incipient and if the
consumption of alcohol is stopped completely, the posterior subcapsular changes
may reverse and even disappear.
References from Forum Comments
1. Klein BE, Klein R, Lee KE,
Meuer SM. Socioeconomic and lifestyle factors and the 10-year incidence
of age-related cataracts. Am J Ophthalmol 2003;136(3):506 512.
2. Chasan-Taber L, Willett WC,
Seddon JM, et al. A prospective study of alcohol consumption and cataract
extraction among U.S. women. Ann Epidemiol 2000;10(6):347353.
3. Manson JE, Christen WG,
Seddon JM, Glynn RJ, Hennekens CH. A prospective study of alcohol
consumption and risk of cataract. Am J Prev Med 1994;10(3):156 161.
4. Simon JA, Hudes ED.
Serum ascorbic acid and other correlates of self-reported cataract among older
Americans. J Clin Epidemiol 1999;52:1207-1211.
5. Mares-Perlman JA, Lyle BJ,
Klein R, et al. Vitamin supplement use and incident cataracts in a
population-based study. Arch Ophthalmol 2000;118:1556-1563.
6. Yamakoshi J, Saito M,
Kataoka S, Tokutake S. Procyanidin-rich extract from grape seeds prevents
cataract formation in hereditary cataractous (ICR/f) rats. J Agric Food
Chem 2002;50:49834988.
7. Waagbø R, Hamre K, Bjerkås
E, Berge R, Wathne E, Lie O, Torstensen B. Cataract formation in Atlantic
salmon, Salmo salar L., smolt relative to dietary pro- and antioxidants and
lipid level. J Fish Dis 2003;26:213-229.
Forum Summary
This population-based prospective
study from Australia utilized repeated lens photographs over a period of 5 to
10 years to diagnose cataracts, relating their development to the reported
alcohol intake of subjects. They also related alcohol to the occurrence
of surgery for cataracts. Previous research has provided some biological
mechanisms that make an association between alcohol and cataracts
plausible.
Overall, the present study showed
little relation between alcohol and cataracts, although adjusted results
suggested a U-shaped association between total alcohol intake and development
of cataract and especially with cataract surgery. These results are
consistent with previous cohort studies. On inspection of the data
presented, the potential reduction in risk of cataract was primarily for wine
and beer. Larger intake of alcohol may be associated with an increased
risk of some types of cataracts.
*
*
*
Comments included in this critique
by the International Scientific Forum on Alcohol Research were provided by the
following:
Andrew L. Waterhouse, PhD, Marvin
Sands Professor, Department of Viticulture and Enology, University of
California, Davis.
David Vauzour, PhD, Dept. of Food
and Nutritional Sciences, The University of Reading, UK.
Pierre-Louis Teissedre, PhD, Faculty
of Oenology ISVV, University Victor Segalen Bordeaux 2, Bordeaux, France.
Erik Skovenborg, MD, Scandinavian
Medical Alcohol Board, Practitioner, Aarhus, Denmark.
Harvey Finkel, MD,
Hematology/Oncology, Boston University Medical Center, Boston, MA, USA.
R. Curtis Ellison, MD, Section of
Preventive Medicine & Epidemiology, Boston University School of Medicine,
Boston, MA, USA.
Links
to other resources
Forum
Archives
Categories
in this forum