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Nutrition and eye health: A clearer view

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Clare Barrett
Accredited Practising Dietitian, Accredited Nutritionist, Marie-Claire O'Shea Dietitians Gold Coast

 

At a time when patients are becoming more proactive about their own health issues and enjoy internet access to myriad nutritional tips, optometrists are facing the same challenge encountered by all health practitioners: sorting the fact from the fiction to provide their patients with clear and
accurate nutrition messages.

I have compiled a few of the most common eye health issues below and offer a brief discussion on their relation to the current understanding of nutrition management. As anyone committed to staying informed of the rapidly-changing field of nutrition knows, certainty is often elusive. The aim of this article is to inspire discussion on the topic of ocular nutrition, not to offer a list of final, irrevocable pronouncements.

Diabetes

It is estimated that about 150,000 Australians suffer from diabetic retinopathy.1 Vascular damage puts a further 850,000 diabetic patients at risk of glaucoma. Dietary advice for diabetes is a broad topic that extends beyond the scope of the optometrist. While the key messages of regular, low-GI food choices can be reinforced, the most effective message that can be given to patients with questions about nutrition is for them to seek advice from a dietitian.

Hypertension

Due to increases in vascular pressure and damage, hypertension increases risk of retinopathy and glaucoma. A reduction in salt intake can improve blood pressure.2 While patients are often conscious of the need to limit added salts, they may be unaware of hidden salts in processed foods.

Encouraging patients to avoid added salt and to limit their intake of processed foods, particularly high-salt savoury snacks, take-away foods and processed meats, is sound advice for optometrists to pass on to patients.

Alcohol excess

In addition to contributing to overall dietary calories, long-term excessive alcohol intake results in the body's reliance on its microsomal ethanol oxidising system (MEOS) for alcohol breakdown. The resultant by-products of this system prevent vitamin A utilisation, leading to night blindness and xerophthalmia. How much alcohol is too much? The National Health and Medical Research Council recommends limiting intake to one or two standard drinks a day.

AMD

Australian supermarket margarines are generally not high in trans fats due to the interesterification processing which does not result in trans fat production. Although butter is considered more `natural' by some, it is high in saturated fat which is associated with coronary heart disease3 and increased progression to advanced AMD.4 The suggestion to choose margarine and use all added fats sparingly is the most sound advice to give to your patients.

A higher intake of omega-3 fatty acids, particularly from oily fish, combined with a lower omega-6 intake may reduce the risk of progression of AMD.4,5,6 The safest message to give to your patients may be to limit overall fat intake, enjoy oily fish regularly and consider the possibly detrimental effects of high omega-6 supplements—including evening primrose oil, black current oil and spirulina.

Clear messages from AMD research indicate that high intake of processed baked goods is associated with a worsening progression, and that fish and nuts in the diet may be protective.5,7 Ginkgo biloba has shown promise in reducing progression in small trials but there is not yet enough evidence for recommendation to patients.8

In 2001, the National Eye Institute's AREDS study showed significant benefits in specific supplements in slowing the progression of AMD.9 As others have shown in this issue of Pharma, the results of the AREDS2 trial, published this year, were surprising and often contentious, leaving room for future studies to provide greater clarification and guidance for the use of ocular nutrition supplements for the prevention of AMD.

Dry eye syndrome (DES)

Omega-3 supplementation has been proposed to reduce symptoms of dry eye, with results of one trial noting improvement in tear production and symptoms in patients.10 These participants received the equivalent of three standard 1,000 mg fish oil capsules, and one standard 1,000 mg flaxseed oil capsule daily.

Higher dietary omega-3 intake has been shown to decrease DES incidence in women and increased risks associated with a high ratio of omega-6 to omega-3.11,12

Cataracts

Currently, there is no good evidence to support any specific nutritional supplements to assist with cataract risk or progression. As well, there are no trials successfully demonstrating improvements in cataracts in either high dose antioxidant supplements or multivitamin supplements.

Conclusion

The evidence is limited on regular supplement use for eye health. Advising the inclusion of dietary omega-3 and nuts, in line with the recommendations of the Heart Foundation may be the most beneficial guidance the optometrist can offer the patient.

The NHMRC's `Australian Guide to Healthy Eating' can easily be accessed by patients on www.eatforhealth.gov.au. Directing patients towards these simple messages is a way for optometrists to feel confident that they are providing sound advice.

In the final analysis, advice on overall healthy eating, with an aim to limit dietary fats, salt and processed items will yield the greatest benefits for your patients.

  1. Australian Institute of Health and Welfare. Eye health facts. http://www.aihw.gov.au/eye-health-facts/.
  2. National Heart Foundation Australia. Salt and Hypertension (Professional Paper): Summary of recommendations for patients with hypertension.  May 2007; PP-555.
  3. National Heart Foundation Australia. Position statement Dietary fats and dietary sterols for cardiovascular health. 2009.
  4. Seddon JM, Cote J, Rosner B. Progression of age-related macular degeneration: association with dietary fat, transunsaturated fat, nuts, and fish intake. Arch Ophthalmol 2003; 121: 12: 1728-1737.
  5. Chong EW et al. Fat consumption and its association with age-related macular degeneration. Arch Ophthalmol 2009; 127: 5: 674-680.
  6. Seddon JM et al. Dietary fat and risk for advanced age-related macular degeneration. Arch Ophthalmol 2001; 119: 8: 1191-1199.
  7. Montgomery MP et al. Overall diet quality and age-related macular degeneration. Ophthalmic Epidemiology 2010; 17: 1: 58-65.
  8. Evans JR. Ginkgo biloba extract for age-related macular degeneration. Cochrane Database Syst Rev 2013; 1.
  9. National Eye Institute. Press Release: NIH study provides clarity on supplements for protection against blinding eye disease. May 2013.
  10. Wojtowicz JC, Butovich I, Uchiyama E et al. Pilot, prospective, randomized, double-masked, placebo-controlled clinical trial of an omega-3 supplement for dry eye. Cornea 2011; 30: 3: 308-314.
  11. Biljana Miljanovic et al. Relation between dietary n3 and n6 fatty acids and clinically diagnosed dry eye syndrome in women. Am J Clin Nutr 2005; 82: 887-893.
  12. Kokke KH, Morris JA, Lawreson JG. Oral omega-6 essential fatty acid treatment in contact lens associated dry eye. Cont Lens Anterior Eye 2008; 31: 3: 141-146.


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