Consumption of polyunsaturated fatty acids (PUFAs) had mixed effects on the risk of glaucoma, data from a national survey showed.
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), members of the omega-3 group, had a protective effect whereas increased total consumption of PUFAs was associated with a higher risk of glaucoma. The apparent contradictory impact might have resulted from confounding factors, including the relative intake of omega-6 and omega-3 fatty acids and comorbid conditions, researchers said in JAMA Ophthalmology.
“This study also hypothesizes that increasing the proportion of dietary omega-3 consumption levels while controlling overall daily PUFA intake may be protective against glaucoma,” Anne L. Coleman, MD, PhD, of the UCLA David Geffen School of Medicine in Los Angeles, and co-authors concluded.
“Because a causal association between daily omega-3 fatty acid (or PUFA intake in general) and the risk of glaucoma could not be drawn in this observational study, additional longitudinal studies or randomized clinical trials are warranted to extend these findings. The role of the dietary consumption of omega-3 relative to omega-6 fatty acid levels also need further elucidation.”
Essential nutrients for human development and health, EPA and DHA occur in large concentrations in certain tissues, including the retina. Clinical studies showed reduced levels of omega-3 fatty acids in patients with glaucoma compared with individuals without the eye disease. Other clinical research showed a lower prevalence of glaucoma in people with a high intake ratio of omega-3 to omega-6 fatty acids.
To continue investigation of PUFAs and glaucoma, Coleman and colleagues analyzed data from the 2005-2008 National Health and Nutrition Examination Survey (NHANES). Examinations performed during the 2005-2008 survey included a standard eye exam, visual field testing, and optic disc photography. A dietary component of the survey provided information about survey participants’ food consumption.
Data analysis included 3,865 NHANES participants ≥40 with complete nutrition interview, laboratory, eye-exam results (which, said the authors, translated to a weighted 83.6 million people in the general population). The primary outcome was prevalence of glaucoma, as defined by the Rotterdam criteria (a combination of optic nerve appearance and visual field defects), as determined by logistic regression analysis. The primary exposure was daily dietary PUFA consumption, estimated from survey participants’ dietary recall interviews and data from U.S. Department of Agriculture resources.
The analysis found a 3.7% prevalence of glaucoma. As compared with people who did not have glaucoma, the glaucoma subgroup was significantly older (mean age 61.4 versus 53.7, P<0.001) and had a higher proportion of non-Hispanic black individuals (23.0% versus 5.2%, P<0.001).
NHANES participants with glaucoma had significantly lower consumption of saturated fatty acids (23.60 versus 26.94 g, P=0.003) and numerically lower consumption of monounsaturated fatty acids (27.52 versus 30.05 g, P=0.07). Dietary consumption of PUFAs did not differ significantly between participants with and without glaucoma (17.22 versus 17.67, P=0.67).
Analysis of PUFA subtypes revealed small but statistically significant differences in consumption of EPA and DHA. The raw-data analysis showed that NHANES participants with glaucoma had mean daily EPA consumption of 8.54 mg compared with 8.50 mg for the participants without glaucoma (P=0.002). The glaucoma subgroup also consumed an average of 34.4 mg of DHA daily versus 33.8 mg for the participants without glaucoma (P=0.04).
However, logistic regression analysis, showed a significant association between mean daily dietary intake of EPA and DHA and a lower risk of glaucoma (OR 0.06, 95% CI 0.00 to 0.73 for EPA; OR 0.06, 95% CI 0.01 to 0.87 for DHA). Intake of other PUFAs assessed by NHANES neither increased nor decreased the risk of glaucoma.
Logistic regression analysis of total PUFA intake and glaucoma risk produced a different statistical picture. NHANES with total daily dietary PUFA intake in the second or third quartile had an increased likelihood of developing glaucoma (OR 2.84, 95% CI 1.39 to 5.79 for second quartile; OR 2.97, 95% CI 1.08 to 8.15 for third quartile), but participants with the highest total PUFA consumption did not have an increased risk of glaucoma (OR 2.03, 95% CI 0.74 to 5.52).
“This finding, although apparently contradicting our finding that increased consumption of EPA and DHA was associated with glaucoma, suggests that even though certain subtypes of PUFAs may reduce the risk of glaucoma, excess PUFA consumption may not,” the authors noted in the discussion of their findings. “Alternatively, the apparently discrepant finding may be secondarily associated with the ratio between omega-3 and omega-6 fatty acid intake.”
A previous large study showed an increased risk of glaucoma in individuals with an omega-3 to omega-6 intake ratio in the highest quintile, they added. The NHANES survey did not capture all omega-3 and omega-6 subtypes, precluding calculation of the ratio.
The authors disclosed no relevant relationships with industry.
F. Perry Wilson, MD, MSCE Assistant Professor, Section of Nephrology, Yale School of Medicine and Dorothy Caputo, MA, BSN, RN, Nurse Planner