The retina is the site for the capturing of visual images in
the eye and it is often likened to the camera film of the eye. The central part
of the retina is called the macula. It is a tiny spot of about 1.4 millimeters
and is yellow in colour due to the high concentration of the pigment, lutein.
Although it is tiny, the macula contains the largest concentration of cone
cells, which are responsible for central high-resolution vision. With aging,
the macula becomes prone to damage and this age-related macular degeneration
(ARMD) is the major cause of loss of central vision in older persons.
Effectively, the central field of vision becomes dysfunctional while the
peripheral vision remains unaffected. Reading or using a computer, becomes
impossible while other activities of daily life remain unaffected. Some types
of ARMD are amenable to treatment with drugs while for others there is no
treatment and thus there has been a drive to seek out preventative measures.
In 2001, researchers from the US National Eye Institute were
the lead authors on a paper which reported that a daily oral supplement with
certain minerals and vitamins, reduced the risk of developing advanced ARMD by
25% over a 5 year period[1].
The research was prompted by several small studies, which suggested a role for
certain antioxidant micronutrients in preventing ARMD. However whereas these
small studies were insufficient to build up a solid base of evidence, they
spurned a phenomenal growth in the sales of food supplements with very
questionable claims. Thus the study, known as The Age Related Eye Disease Study
(AREDS), enrolled 3,640 subjects with ARMD to test the hypothesis that certain
micronutrients might reduce the progressions of the disease. The results showed
a reduction in ARMD progression with daily supplements of vitamin C, vitamin E,
beta-carotene, zinc and copper.
In May of this year, a second AREDS paper was reported in the
Journal of the American Medical Association[2].
This study sought to further explore whether additional micronutrients might
enhance the effects of the first AREDS micronutrient cocktail. The first of the
micronutrients was lutein, which is found in high concentration in the macula.
It is synthesised only by plants, particularly green leafy plants and in the
eye, serves to protect the retina from damage arising through the high-energy
photons of blue light. Zeaxanthin, the
second micronutrient is also involved in photo quenching in the macula and,
again, it is a plant derived compound. The final two additional compounds examined
were the very long chain polyunsaturated fatty acids found in high
concentration in oily fish and which also form a main element of the
surrounding of nerve calls (the myelin sheath). The eye is a very heavily
innervated organ. The outcome of this second AREDS study was that there was no
additional benefit to be had over and above what had been achieved with the
original AREDS cocktail (vitamin C, vitamin E, beta-carotene, zinc and copper).
Yet another paper[3]
recently focused on other micronutrients and their role in ARMD, specifically
two B vitamins, folic acid and vitamin B12. Volunteers had retinal photographs taken 5 to 10
years apart and the incidence of ARMD was ascertained using these retinal
photographs. At entry into the study, subjects complete a food frequency
questionnaire, which was used to ascertain habitual folic acid and B12 intakes. Blood samples were
taken to ascertain the biochemical status of the vitamins. The use of
nutritional supplements was also recorded. After statistical adjustment for
such confounding factors as age, smoking, gender, and so on, those deemed to be
deficient in folic acid status using blood measures, had an 89% increased risk
of ARMD. B12 deficiency
increased the 10-year risk of ARMD by about 60%. Those subjects who were
regular users of food supplements had a 47% lower risk of macular degeneration.
This study was observational and cannot prove cause and effect for which a
long-term intervention study (such as AREDS 1 and 2) is needed.
ARMD accounts for more
than 50% of all blindness in the US and the numbers affected will grow from
about 2 to 4 million by 2025. Clearly, ARMD will continue to be a major area of
public health nutrition. And once again, all this research shows that the old adage
that all your nutrients can be had derived entirely from a health diet isn’t true.
No doubt it is true for some but not all and nutrigenetics will soon reveal who
is most sensitive to low micronutrient intakes in relation to ARMD.
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