Age-related macular degeneration and dietary supplements

Age-related macular degeneration (AMD) is the leading cause of severe central vision loss and legal blindness in the population over 60 years of age.

It is a disease that arises from a complex interaction between several factors, first and foremost age, as the risk of developing the disease increases significantly in people over 65.

In addition to age, there are other risk factors: demographic (ethnic factor, gender), genetic and environmental (family history, smoking, alcohol consumption, diet high in saturated fat and low in fish, fruit and vegetables, obesity, low physical activity, prolonged exposure to sunlight.

An additional risk factor is the presence of pre-existing diseases, such as diabetes.

Classification

AMD (Age-Related Macular Degeneration) is a chronic degenerative disease, progressive and tending to become bilateral, affecting the macula, the central region of the retina responsible for distinct vision of image details.

Two forms of AMD are recognised:

- the 'dry' form, which affects approximately 90% of all macular degeneration, characterised by the accumulation below the macula of deposits of yellowish material, the drusenwhich progressively alter the functionality of photoreceptors, cells responsible for the perception of light stimuli;

- the 'wet' form, fortunately less frequent than the dry form, but with a more disabling outcome, characterised by the formation of small abnormal blood vessels below the macula. These vessels, with very fragile walls, can easily ooze fluid, or they can rupture, causing haemorrhages in the retina.

Late AMD is the pathological condition most associated with the risk of blindness and occurs in two forms: geographic atrophy (GA) and neovascular AMD.

Symptoms

AMD initially manifests as a gradual reduction in visual acuity associated with an altered and distorted perception of images (lines appear wavy). One may need more light to read and may have difficulty recognising people unless they are very close. It is sometimes manifested by the presence of opaque spots (scotomas) in the centre of the visual field, but often the symptoms are masked by the fact that the problem only affects one eye.

In the 'dry' form, the loss of central vision occurs slowly and progressively and it is possible to see a black spot in the centre of the visual field. When suffering from the 'wet' form of the disease, the loss of central vision is unfortunately very rapid.

If any of the described symptoms appear, an eye examination should be carried out as soon as possible.

Laser photocoagulation and photodynamic therapy

For the treatment of the wet form, there are now numerous treatment options, from traditional ones such as laser photocoagulation and photodynamic therapy (PDT) to the more recent anti-angiogenic drug therapy.

Laser photocoagulation involves focusing a particularly powerful laser beam to destroy abnormal vessels that form in the retina.

In some cases, it is then possible to use photodynamic therapy (PDT), which selectively destroys abnormal blood vessels through the intravenous injection of a photosensitive pharmacological substance that is activated by laser treatment.

Intravitreal therapy with anti-VEGF drugs

The important and revolutionary therapeutic innovation is the administration by intravitreal injection of certain anti-angiogenic substances, which are able to counteract the formation of neovases (pegaptanib, ranibizumab, bevacizumab, aflibercept).

Neovascular AMD is today mainly treated with intravitreal injections, which have to be repeated over time, of anti-VEGF drugs, whereas no treatment is currently available for GA. Precisely for this reason, preventive approaches can be very useful for both late disease subtypes.

Medical therapy

It is known that taking food supplements with specific combinations of antioxidants and minerals can decrease the risk of progression from intermediate to late age-related macular degeneration, particularly in the case of the neovascular form.

In addition, observational studies have shown that a higher intake of specific nutrients is associated with a change in the risk of developing AMD.

In particular, it has been observed that a reduced risk of progression of age-related macular degeneration is associated with a higher intake of omega-3 fatty acids and carotenoids (lutein and zeaxanthin), taken either through diet or supplements.

Two recent studies, conducted on more than 8,000 patients, have shown that the adoption of a Mediterranean diet, and in particular its fish component, is strongly associated with a decrease in progression to late AMD, particularly to geographic atrophy.

Foods that reduce the risk of ELM progression

Several nutrients have been associated with a lower risk of AMD progression.

These include long-chain polyunsaturated fatty acids (LC-PUFA), omega-3, minerals (e.g. copper, magnesium and selenium), B vitamins and antioxidant carotenoids (e.g, β-carotene and lutein/zeaxanthin).

It seems, therefore, that a Mediterranean-type diet or the intake of certain individual food components may play an important part in counteracting the progression of this disease.

LC-PUFA and omega-3

Fish consumption is thought to play a key role. Intake of LC-PUFA and omega-3 has, in fact, been correlated with a lower risk of AMD progression, as has also been found in many studies published in the literature.

The reason is that these two types of nutrients produce anti-inflammatory and anti-angiogenic metabolites.

Prevention through nutrition

Fish also contains large amounts of B vitamins, the intake of which has been associated with a 34% reduction in the incidence of AMD.

One possible mechanism by which an adequate intake of folic acid and vitamins B6 and B12 would protect against AMD could be the prevention of increased serum homocysteine. The latter, in high amounts, is in fact an independent risk factor for neurodegenerative and cardiovascular diseases and has also been associated with AMD.

Certain minerals contained in fish, including copper, iron, magnesium and selenium, may also reduce the risk of ELD progression.

Not only fish, but also fruit and vegetables contain abundant amounts of antioxidant nutrients, which are associated with a decreased risk of ELM progression. These include vitamin C, pro-vitamin A carotenoids (α-carotene, β-carotene and β-cryptoxanthin) and lutein/zeaxanthin.

Foods that may increase the risk of ELM progression

A higher intake of certain nutrients seems, on the other hand, to be associated with an increased risk of late AMD progression. These are, in particular, unsaturated and monounsaturated fats and oleic acid. The primary sources of unsaturated and monounsaturated fats are meat, dairy products and sugary, high-fat, low-nutrient-density foods.

Conclusions

In conclusion, increased dietary intake of certain types of nutrients is associated with a reduced risk of AMD progression, including: minerals, vitamins and carotenoids. This positive association applies to both subtypes of late-stage AMD, but is particularly evident for geographic atrophy, for which no treatment is currently available. These nutrients can also be taken through dietary supplementation. Diet and oral supplementation may, therefore, play complementary roles in reducing the risk of progression of age-related macular degeneration.

Elvira Agrón et al, Dietary Nutrient Intake and Progression to Late Age-Related Macular Degeneration in the Age-Related Eye Disease Studies 1 and 2, VOLUME 128, ISSUE 3, P425-442, MARCH 01, 2021, DOI:https://doi.org/10.1016/j.ophtha.2020.08.018