Foods to stop you going blind

Tuesday September 11 2007

Two nutrients found in green vegetables and eggs have been found to protect against developing age related macular degeneration (ARMD), a condition that can lead to blindness, Reuters news agency reported. The two nutrients, lutein and zeaxanthin, which are found in eggs and leafy vegetables such as spinach, are thought to work partly by helping eyes to filter out short wavelength light, which can damage the retina at the back of the eye.

This news story is based on a case-control study; further trials are needed to test whether these nutrients can truly reduce the risk of developing ARMD before we can draw any firm conclusions.

It is still recommended that a balanced diet, with fruit and vegetables, is one of the best ways to stay healthy.

Where did the story come from?

Doctors belonging to the Age Related Eye Disease Study research group (Areds) from research centres in the US, carried out this research. The study was funded by the National Eye Institute, National Institutes of Health, US Department of Health and Human Services, and Bausch and Lomb, New York.

The study was published in the peer-reviewed medical journal Archives of Opthalmology .

What kind of scientific study was this?

This was a case control study.

Over a six-year period, researchers enrolled around 4,800 volunteers aged 55 to 80 years old, who had at least a certain level of vision in one eye, which did not have advanced ARMD or any other eye disease that could interfere with the assessment of ARMD.

Researchers gave the volunteers detailed eye examinations, and divided them into five groups: one group had no signs of ARMD in either eye (the control group), and the other four groups had increasingly severe eye defects that indicated that they were developing ARMD (the case groups). The group with the most severe signs was classified as having neovascular ARMD (where there is development of new, fragile blood vessels over the affected retina).

The volunteers then completed questionnaires, asking their medical history, use of prescription medication and vitamin and mineral supplements and whether they smoked. They also answered 90 questions about their food consumption, which asked them to estimate how often they had eaten particular foods or drinks in the previous year, and how big the portions that they ate or drank were.

Researchers, who were unaware whether participants had ARMD or not, used computer software, to estimate how much of seven different nutrients each person had consumed. Statistical analysis was then carried out to assess whether the risk of developing signs of ARMD differed with different intakes of these nutrients.

When analysing the results, efforts were made to ensure that the age, gender and overall energy intake of the case and control volunteers were as similar as possible. As a result, only the data from 4,519 people aged 60 to 88 years old was used in the analysis.

What were the results of the study?

The researchers found that people who had the highest intake of the two nutrients, lutein and zeaxanthin, in their diet were less likely to develop ARMD than those with the lowest consumption of these nutrients. They found no independent differences in the risk of developing ARMD with using any of the other dietary nutrients or supplements.

What interpretations did the researchers draw from these results?

The researchers concluded that a high dietary intake of lutein and zeaxanthin reduced the risk of developing neovascular ARMD, or the more advanced signs of ARMD. They suggest that if these results are confirmed in other studies, these nutrients might be used as supplements or in dietary interventions to prevent ARMD.

What does the NHS Knowledge Service make of this study?

This was a relatively large case-control study, which appears to be reasonably reliable. However, we need to consider the limitations of this type of study when interpreting the results, which the authors acknowledge:

  • People find it difficult to accurately remember what food they have consumed over the past year. They can also be prone to reporting eating more healthy foods than they actually did to avoid feeling guilty about having a poor diet. When contrasting the group with eye disease with the group without, these factors would be particularly problematic as those with eye disease might be generally less healthy.
  • Calculating the amount of nutrients in food is based on a number of assumptions, for example, what size a ‘portion’ might be, or that a standard amount of a nutrient is found in a food. This may also lead to inaccuracies in the nutrient intake calculated for each person.
  • The study does not specifically report which types of food people ate to get these nutrients; therefore we cannot identify the best source for these nutrients in food.
  • Many factors will play a role in the development of ARMD, age itself being by far the greatest risk factor. Although the researchers have attempted to adjust for certain risk factors, we still cannot be sure that it is these specific nutrients that are causing the reduction in ARMD.
  • We cannot be certain how these nutrients might play a role in the development of ARMD, as the biological basis for this improvement was not investigated in this study.

Further trials are needed to test whether these nutrients can truly reduce the risk of developing ARMD before we can draw any firm conclusions.

Regardless of whether or not your diet can effect your risk of developing ARMD, eating a healthy balanced diet which includes plenty of fruit and vegetables, has many benefits and is recommended.

Sir Muir Gray adds…

It is essential to keep testing natural sources for new treatments, and is one of the reasons why we should protect the biodiversity of our planet.

Analysis by Bazian
Edited by NHS Choices