Eggs and Eye Health

Position Statement for Healthcare Professionals

Eggs and Eye Health

 

Updated June 2016

In recent years, age-related eye disorders have been reported as the leading causes of vision impairment and blindness in Australia. These disorders include cataracts, age-related macular degeneration (AMD), diabetic retinopathy and glaucoma, with age-related macular degeneration being the most common cause of blindness. The major risk factors for age-related eye disorders include smoking, family history and increasing age. AMD also appears to be more likely in men than women although this differs between  countries. Given Australia’s ageing population, eye health will become an increasingly important health issue to address. However, eye disorders are not only a problem for older adults. For example, eye disorders are among the most common long-term health problems experienced by Australian children. Evidence indicates that several dietary factors such as antioxidant intake, fat types, omega-3 intake, glycemic index and adequate intake of key vitamins and minerals play an important role in the development and progression of some of these disorders including AMD and cataracts. People with diabetes, in particular, have an increased risk of developing eye disease. The 2003  Australian Diabetes, Obesity and Lifestyle Study found that 15.3% of people with known diabetes and newly diagnosed diabetes had developed retinopathy. This is similar to findings from a 2015 Australian study which found evidence of diabetic retinopathy in 16% of study participants. Improved diabetes control, which ideally involves dietary and lifestyle modification, reduces the risk of developing, and the progression of, diabetic retinopathy.

Antioxidants and Eye Disease –

Lutein and zeaxanthin (with their isomer meso-zeaxanthin) are the primary carotenoids found in the macular region of the retina. Numerous studies have suggested lutein and zeaxanthin, (along with other nutrients such as omega-3), are essential components for eye health. As the retina suffers progressive oxidative damage with age, it is thought that lutein and zeaxanthin play a protective role in the prevention of eye disease. Lutein accumulates in the front of the macula and macular pigment density is inversely associated with AMD. In reviews of human studies, evidence suggests dietary intake of lutein and zeaxanthin can lead to their accumulation in the retina, and as a result may provide protection against retinal degeneration. Furthermore, a review of population studies has shown that lutein and zeaxanthin (from plant sources) may also provide protection against age-related cataracts and AMD.

The Blue Mountains Eye Study (BMES) showed that for dietary lutein and zeaxanthin, elderly participants in the top tertile of intake had a reduced risk of developing late AMD (RR 0.35) and research has also found that nearly 80% of those with wet AMD have a deficient intake of lutein and zeaxanthin. In 2012, a systematic review found that while dietary lutein and zeaxanthin were not significantly associated with a reduced risk of early AMD, these important antioxidants may protect against late AMD. Studies published since then have also suggested that the benefits of lutein and zeaxanthin for AMD may be limited to advanced AMD.

Furthermore in the AREDS (Age-Related Eye Disease Study) 1 study, investigating the effectiveness of a nutritional supplement on eye health, investigators found the dietary information pointed to lutein and zeaxanthin as being protective against developing AMD. Given this, a further study (AREDS2) was conducted which incorporated lutein (10mg) and zeaxanthin (2mg) into the supplement being used in the study. In secondary analysis, lutein and zeaxanthin supplements on top of the AREDS supplement lowered the progression to advanced AMD in persons with low dietary lutein and zeaxanthin. A reduction in risk was seen for individuals in Quintile 1 (median of 696ug lutein and zeaxanthin per day). For those with a median intake of 1134ug per day the HR was 0.94 showing that the supplement lost its effect if the background diet was sufficient enough in lutein and zeaxanthin. 

Furthermore data from the BMES and the Rotterdam Study indicates that individuals at high risk of AMD (ie, those genetically susceptible to AMD) appear to benefit from a high lutein and zeaxanthin intake. Among participants with high genetic risk, the highest intake of lutein and zeaxanthin was associated with a >20% reduced risk of early AMD. No similar association was evident among participants with low genetic risk.

Several mechanisms have been proposed as to how lutein and zeaxanthin may protect the eye including through the absorption of damaging blue light and via the antioxidant properties of these compounds which protect the retina and photoreceptors in the eye against free radical damage. One study showed that retinal lutein and zeaxanthin reduce glare disability and discomfort, reduce photostress recovery times, and enhance contrast.  Other evidence suggests that lutein plays a systemic anti-inflammatory role which may help protect against AMD. Although it is unclear why some people develop AMD it has been suggested there may be a problem with the uptake of lutein and zeaxanthin by the eye likely caused by a variation in genes related to carotenoid transport, uptake and metabolism.

Eggs contain both of the antioxidants lutein and zeaxanthin, with one serve* of eggs containing around 530ug. While this is lower than some plant sources, it has been shown that a number of factors effect the bioavailability of carotenoids. For example, the consumption of fat (in the form of a salad dressing, cooking oil or whole eggs) at the same meal as carotenoid intake (eg, a raw vegetable salad or cooked vegetables) has been shown to effectively increase the absorption of some carotenoids. Bioavailability of carotenoids may be decreased due to competition for absorption between carotenoids when consumed within the same meal.  Furthermore dietary fibre from plant sources, such as pectin and guar gum, has been shown to reduce carotenoid absorption and the localisation of carotenoids within the chloroplasts and chromoplasts of plants may decrease bioavailability.  

Regular egg consumption (between 1 and 3 eggs per day for 4-12 weeks) has been shown to effectively increase plasma lutein concentrations by 21-50% and zeaxanthin concentrations by between 48-100%. In contrast, spinach and corn, although having a high content of zeaxanthin, do not raise plasma zeaxanthin concentrations.  

Currently there is insufficient research to indicate an exact optimal level of intake of lutein and zeaxanthin for protecting against eye disease, although some researchers have recommended levels as high as 6mg per day. However evidence from both the AREDS2 study and the BMES suggest levels of intake of lutein and zeaxanthin considerably less than 6mg are associated with a decreased likelihood of AMD indicating lower levels of intake may be sufficient to provide some protection from progression of the disease, although further intervention studies to ascertain an appropriate target level, particularly for individuals at high risk of AMD are needed. However data from the BMES indicates that in older Australians, those with a dietary lutein and zeaxanthin intake of more than 942ug/day, along with the highest intake of vegetables, were less likely to develop AMD. Furthermore, in the AREDS 2 study, the quartile with a median intake of 1134ug lutein and zeaxanthin from dietary sources, had a HR of 0.94 indicating this dietary amount was sufficient to reduce the effects of the supplement that were shown when individuals consumed less lutein and zeaxanthin in their diet.

Earlier reports from the BMES showed that women had slightly higher intakes of lutein and zeaxanthin compared to men. The main contributors to lutein and zeaxanthin intakes were broccoli, green beans and oranges. No other Australian studies have assessed the intake of these antioxidants in other population sub-groups however current intakes in older adults are lower than ideal.

Due to both their high bioavailabilty and not being subject to seasonal variation, the consumption of eggs is a favourable source of lutein and zeaxanthin in the diet.

Antioxidants and Eggs

No studies have specifically investigated the association between antioxidants from eggs and eye disease risk. However, in the Beaver Dam Eye Study, egg consumption was inversely associated with nuclear cataract risk among members of the cohort who were less than 65 years of age at baseline. Persons in the highest quintile of egg consumption had a 60% lower risk of developing cataract compared to those in the lowest quintile of intake after adjustments for age and energy intake. 

A number of studies have assessed egg consumption as a vehicle for increased uptake of the antioxidants lutein and zeaxanthin, with results showing egg consumption effectively raises blood carotenoid levels and in some studies macular pigment optical density (MPOD). The level of increase differed in the studies dependent on level of egg consumption (1 to 4 eggs per day), duration of study and type of eggs used (regular verses lutein enriched). Furthermore, LDL cholesterol levels were not found to increase despite the increases in carotenoid levels with egg consumption.

In one 2014 study conducted using lutein and/or zeaxanthin enriched eggs, feeding healthy individuals eggs (lutein content (920-970ug); zeaxanthin content (340-487ug)) lead to significant increases in blood levels of both lutein and zeaxanthin. The increases were comparable to the daily use of a 5mg supplement. Despite these increases, no increases in lutein/zeaxanthin levels in the macular were detected, although the researchers suggested this was most likely due to the length of the study rather than the ineffectiveness of the intervention.

Overall, the research to date suggests that eggs are a highly bioavailable source of dietary carotenoids (lutein and zeaxanthin)  and that they are an effective vehicle for increased and site-specific antioxidant uptake. This in turn may have benefits for long term eye health given the data supporting the role of lutein and zeaxanthin. 

Omega-3 Fats and Eye Health

The essential long chain omega-3 fatty acid docosahexaenoic acid (DHA) is a major structural lipid found in the photoreceptors of the retina, affecting the permeability, fluidity and thickness functions of the photoreceptor membranes. Deficiency of DHA is associated with alterations in the functioning of the retina and visual processing. Adequate intake of long-chain omega-3 can protect the eye from retinal damage caused by ischemia, oxidation, light, inflammation and age-associated diseases. Some research has shown that lower intakes of saturated fat and higher intakes of omega-3 fatty acids are protective against the development of certain eye diseases, while vegetable fats and monounsaturated fats are associated with a greater risk of developing advanced AMD. However, the Blue Mountains Eye Study of 3654 persons aged 49 years and over, found no association between incident AMD and butter, margarine, or nut consumption.

Overall, research in the area of fats and eye disease is somewhat limited and the results mixed, however there is some consistency in the finding that higher intakes of fish and/or omega-3 fats may be protective. While individuals studies have found associations between the consumption of omega-3 and/or omega-3 status and a reduced risk of AMD, a 2015 Cochrane review found that omega 3 supplementation in people with AMD who have had the disease for periods of up to five years, does not reduce the risk of progression to advanced AMD or the development of moderate to severe visual loss.  The review concluded that currently available evidence does not support increasing dietary intake of omega 3 LCPUFA for the explicit purpose of preventing or slowing the progression of AMD.

Of note, in 2010, the European Food Safety Authority (EFSA) asserted that consuming 250mg of DHA per day (in one or more servings), can make an important contribution towards maintaining vision in the general population.

Other Nutrients in Eggs 

In addition to lutein and zeaxanthin, adequate intakes of vitamin A, other antioxidants and zinc are thought to reduce the amount of visual degeneration in the elderly. For example, results from the BMES showed that those consuming the highest amount of zinc per day (>15.8mg/day) were significantly less likely to develop AMD than the remaining population. For people aged 51 years and over, one serve of eggs* provides bioavailable vitamin A (34% RDI for women, 27% RDI for men), vitamin E (34% AI for women, 24% AI for men), selenium (68% RDI for women, 59% RDI for men), and zinc (6% RDI for women, 4% RDI for men). 

Dietary and lifestyle effects on eye health

Studies have linked diet quality, glycemic index (GI) and body mass index (BMI) with eye health. Studies using data from the BMES have shown older adults with higher diet quality (better compliance with dietary guidelines) also had healthier retinal vessels and a decreased long term risk of visual impairment. With respect to glycemic index, despite older research showing no evidence of a high glycemic index diet increasing the risk of cataracts, a 2006 study indicated that people with the highest GI diets were 1.29 times more likely to have nuclear opacities (cataracts) than those with lower GI diets. Results from a 2007 study also found that those consuming a diet with a high GI (>77.9 for women and 79.3 for men) had a 49% increase in the risk of AMD, and that 20% of prevalent cases of AMD would have been eliminated if participants had a dietary GI below these values. Results from the Nurse’s Health Study and the BMES also indicated a high GI diet is associated with the development of AMD

BMI is another modifiable lifestyle factor associated with AMD. The Age-Related Eye Disease Study (AREDS) showed obese people with early or intermediate AMD were almost twice as likely to develop central geographic atrophy (lesions associated with dry AMD), and thus progress to advanced AMD, when compared to non-obese people. In addition, the impact of egg consumption on plasma lutein levels appears to be influenced by body mass index and waist circumference. Increased abdominal fat has also been significantly associated with age-related macular degeneration.

Given the nutritional composition of eggs, they can make a valuable contribution to improved diet quality, help lower the GI of a meal and may have a role to play in assisting weight management through appetite control. 

Conclusion

Eggs contain a range of nutrients and antioxidants that have been shown to contribute to long-term eye health. Eggs can therefore be enjoyed regularly as part of a healthy lifestyle that also includes the following:

  • Smoking avoidance
  • Enjoying 1-2 fish meals per week
  • Eating other foods rich in carotenoids such as dark green and orange/yellow fruit and vegetables daily
  • Reducing dietary sources of saturated fat
  • Exercising regularly to control body weight and blood pressure
  • Reducing the glycaemic index of the diet
  • If overweight, aiming for weight loss to assist with controlling blood glucose levels and fat loss
  • For people with type 2 diabetes, achieving and maintaining optimal blood glucose and plasma lipid levels.

 

This statement is for healthcare professionals only.

*One serve = 2x60g eggs (104g edible portion)

 

RDI: Recommended Dietary Intake

AI: Adequate Intake

 

Useful links:

http://www.mdfoundation.com.au/

http://www.visionaustralia.org/eye-health/eye-conditions/age-related-macular-degeneration

 

 

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