Sticking to the theme of eye health I wanted to briefly write about cataracts today.  Cataracts are cloudy areas that develop in the lens of the eye, the cloudiness reduces the amount of light transmitted to the retina and this causes poor vision.  In the UK about 1 in 3 people over the age of 65 develop a cataract, which gradually forms over many years.  Initially vision may only be very mildly affected and this may not progress, however, in some individuals the vision will get worse over time. 

Treatment is an option when a cataract becomes bad enough to interfere with normal life e.g. if vision starts to interfere with reading, driving, watching TV etc or stops an individual from doing anything that they would normally do.  Before making a decision about treatment it is recommended to make sure your glasses are giving you maximum benefit.  Treatment involves the removal of the cloudy lens and replacement with an artificial plastic lens (an intraocular implant).

Cataracts seem to occur due to the breakdown and subsequent clumping of proteins in the lens.  Obviously, prevention is always better than cure!  Lifestyle factors that may increase the risk of cataract development include a poor diet low in antioxidant nutrients (found in fruits and vegetables), smoking and prolonged sunlight exposure.  Again, as with AMD, free radicals appear to play a causal role and hence dietary antioxidants may be protective.

I would like to highlight three (1,2,3) very recent research studies.  The first study(1) looked at the association between cataracts and dietary lutein and zeaxanthin, caroteinoids found in spinach, collard greens and kale.  The study involved 1802 women aged 50 to 79 years.  Women with high dietary levels of lutein and zeaxanthin had a 23% lower prevalence of cataract compared to those with low levels.  Women with the highest dietary intakes or highest blood serum levels of lutein and zeaxanthin as compared with those with the lowest were 32% less likely to have cataract.  For more information on these carotenoids and potential supplements please refer to Monday's post which looked at AMD.

The researchers involved in the second study(2) wanted to investigate the relationship between antioxidant nutrient intakes and incidence of age-related cataract over a 10 year period.  The study involved 2464 individuals (aged 49 or over at the start of the study) for 5-10 years.  Eye health was observed using lens photography and dietary intakes of various antioxidants, including zinc, beta carotene, vitamins A, C and E, was assessed.  Individuals with the highest total intake, from diet and supplements, of vitamin C had a 45% reduced risk of cataract.  An above average intake of combined antioxidants -vitamins C and E, beta-carotene, and zinc - was associated with a 49% reduced risk of cataract.  The authors of the study conclude that “Higher intakes of vitamin C or the combined intake of antioxidants had long-term protective associations against development of nuclear cataract in this older population”.

Both of these studies, as in the studies I highlighted in relation to eye health on Monday, re-iterate the importance of a diet rich in vegetables and fruits, which are fabulous sources of antioxidants.  As yet the role for supplementation in the prevention of cataract is unclear (and cannot, of course, substitute diet) but many individuals are taking multivitamin and mineral supplements to help keep their eyes, and bodies, healthy.  Future large supplementation trials are planned and I look forward to seeing the results.

The third study(3) involved around 2000 individuals aged 49 or over (at the start of a 5 year investigatory period).  The researchers found that higher dietary intakes of omega-3 polyunsaturated fatty acids were associated with a significantly reduced risk (42% compared to those with the lowest intakes) of developing cataract over 5 years.   For more information regarding omega 3 fatty acids and eye health please refer to the piece that I posted on Monday which looked at AMD.

(1)Moeller SM et al.  2008.  Associations between age-related nuclear cataract and lutein and zeaxanthin in the diet and serum in the carotenoids in the age related eye disease study, an ancillary study of the women’s health initiative.  Arch Opthalmol.  126:354-364
(2)Tan AG et al.  2008.  Antioxidant intake and the long-term incidence of age-related cataract: the blue mountains eye study.  Am J Clin Nutr.  87:1899-1905
(3)Townend BS et al.  2007.  Dietary macronutrient intake and five year incident cataract: the blue mountains eye study.  Am J Opthalmol.  143:932-939.

Written by Ani Kowal

My eyesight is something that I value very highly.  Without my spec's or contact lenses I have very limited vision.  Looking after my eyes, in order to prevent further long-sightedness in later life, is certainly high on my agenda.  Age Related Macular Degeneration (AMD) is the most common cause of blindness in people over the age of 50 in the UK and I feel that it deserves a little attention! 

The macular is the light sensitive area in the centre of the retina that controls visual field and the ability to see colours.  AMD is caused by the deterioration of the macular.  As this happens the peripheral, outer, vision remains intact as the centre field of vision becomes slowly blurry, grey or filled with a large black spot.  Two forms of AMD exists: the dry form which develops slowly, accounting for 90% of all cases; and the wet form which causes rapid deterioration of central vision.

The exact causes of AMD are unknown although free radical damage, where unstable oxygen molecules damage the eye cells, is strongly implicated.  Tobacco smoke and sun exposure can increase the level of free radicals in the body and both are a risk for AMD.  High blood pressure and diabetes are also risk factors as these conditions can limit blood flow to the eyes.

Evidence for diet and nutrition in the prevention, and to a certain extent treatment, of the condition is growing yearly.  The latest study was published in the August volume of the American Journal of Clinical Nutrition(1) and adds to the growing body of research(2,3,4,5,6,7,8) suggesting that oily fish and the long chain omega 3 fatty acids they provide, EPA and DHA (eicosapentaenoic acid and docosahexaenoic acid), may be preventative. 

This recent study(1) assessed the dietary intake data and photographic eye evidence of 105 individuals with AMD and compared it to 2170 control individuals (without any features of AMD).  All participants were aged 65 or over.  The researchers found that eating oily fish at least once per week compared with less than that was associated with a 50% reduced likelihood of having AMD.  There was no benefit from eating non-oily, white fish.  There was also a strong significant association between intake levels of DHA and EPA and AMD.  Individuals eating around 300mg or more of these fatty acids per day were 70% less likely to have AMD.  Two (75g) servings of oily fish, such as salmon, mackerel, sardines or trout, provides around 500mg of DHA and EPA 

The scientists are not yet recommending omega 3 supplements as the study did not investigate whether supplements would have the same benefit as dietary sources.  However, evidence for the potential benefits of fish oil (long chain omega 3 fatty acid) supplements is beginning to emerge, with one very recent study(5) finding that 800mg of DHA per day over 2-4 months was associated with beneficial changes in the macular. 

Omega 3 fatty acids are incredibly important for many aspects of health (and I have mentioned them throughout my blog postings).  Including at least two portions of oily fish per week is certainly recommended, however, many individuals in the UK do not achieve these intakes for various reasons.  A daily fish oil supplement providing around 250mg of EPA and 250mg DHA may be something worth considering (for general health).  For vegetarians and vegans a flaxseed oil supplement providing around 500-800mg of alpha-linolenic acid (a short chain omega 3 fatty acid which the body can convert to the longer chain forms) daily is a good way of ensuring a daily supply of these essential fats.

The other important nutrients worth discussing in relation to AMD prevention are the antioxidant carotenoids lutein and zeaxanthin, naturally found in foods such as spinach, collard greens and kale.  Research data(9,10,11,12) suggests that individuals with high dietary intakes of lutein and zeaxanthin, and high body levels of the carotenoids, have a reduced risk of developing AMD.  Supplements of these nutrients are now widely sold and targeted at eye health.  The supportive evidence for supplementation is not yet solid.  A small study(13) has shown benefit and paves the way for larger studies.  A very recent review(14) of the currently available evidence, published last month, concluded that “A definite association between lutein and zeaxanthin supplementation and clinical benefit has yet to be hown; however, it may still be an appropriate cautionary measure for patients at high risk for developing AMD”

Available ‘eye health’ supplements often contain vitamins C, E, beta carotene and the mineral zinc in addition to lutein and zeaxanthin.  The rationale behind this comes from dietary association studies and some research evidence.  If you are considering supplements remember that they are not a substitute (more of a bonus) for nutritious daily meals!  A healthy diet, rich in a variety of vegetables and fruits, will provide an array of antioxidant nutrients to keep the whole body healthy, including the eyes.

(1)Augood C et al.  2008.  Oily fish consumption, dietary docosahexaenoic acid and eicosapentaenoid acid intakes, and associations with neovascular age related macular degeneration.  American Journal of Clinical Nutrition.  88:398-406
(2)Chong EW et al.  2008.  Dietary omega-3 fatty acid and fish intake in the primary prevention of age-related macular degeneration: a systematic review and meta-analysis.  Arch Ophthalmol.  126:826-833.
(3)SanGiovanni JP et al.  2007.  The relationship of dietary lipid intake and age-related macular degeneration in a case-control study: AREDS Report No. 20.  Arch Opthalmol.  125:671-679
(4)Seddon JM et al.  2006.  Cigarette smoking, fish consumption, omega-3 fatty acid intake, and associations with age-related macular degeneration: the US Twin Study of Age-Related Macular Degeneration.  Arch Opthalmol.  124:995-1001
(5)Johnson EJ et al.  2008.  The influence of supplemental lutein and docosahexaenoic acid on serum, lipoproteins, and macular pigmentation.  Am J Clin Nutr.  87:1521-1529
(6)Cho E et al.  2001.  Prospective study of dietary fat and the risk of age-related macular degeneration.  Am J Clin Nutr.  73:209-218
(7)Seddon JM et al.  2001.  Dietary fat and risk for advanced age related macular degeneration.  Arch Opthalmol.  119:1191-1199
(8)Smith W et al.  2000.  Dietary fat and fish intake and age related maculopathy.  Arch Opthalmol.  112:222-227
(9)Seddon JM et al.  1994.  Dietary carotenoids, vitamin A, C and E and advanced age-related macular degeneration.  JAMA.  272:1413-1420
(10)Bone RA et al.  2000.  Lutein and zeaxanthin in the eyesm serum and diet of human subjects.  Experimental Eye Research.  71:239-245
(11)Bone RA et al.  2001.  Macular pigment in donor eyes with and without AMD:A case-control study.  Invest Opthalmol Vis Sci.  42:234-240
(12)Gale CR et al.  2003.  Lutein and zeaxanthin status and risk of age-related macular degeneration.  Invest Opthalmol Vis Sci.  44:2661-2465
(13)Richer S et al.  2004.  Double-masked, placebo-controlled, randomised trial of lutein and antioxidant supplementation in the intervention of atropic age related macular degeneration: the Veterans LAST study (Lutein Antioxidant Supplementation Trial).  Optometry.  75:216-230)
(14)Zhao L & Sweet BV.  2008.  Lutein and Zeaxanthin for macular degeneration.  Am J Health Syst Pharm.  65:1232-1238

Written by Ani Kowal