Extra supplements don’t slow macular degeneration
Additional supplements containing lutein, zeaxanthin, and omega-3 fatty acids don’t seem to slow the progress of age-related macular degeneration, a new study finds.
BMJ Group News
What do we know already?
Age-related macular degeneration (AMD) is a major cause of poor sight in older people. AMD damages the macula, a tiny spot of nerve tissue at the back of the eye, which is responsible for central vision. When AMD becomes serious or ‘advanced’ it can cause complete loss of vision.
We don’t know exactly what causes AMD and there are no known cures. However, giving up smoking and taking certain supplements can slow the rate at which the disease progresses.
For example, an earlier study showed that people with AMD who take a supplement of vitamin C, vitamin E, beta carotene, zinc, and copper could reduce by a quarter their chance of the condition becoming advanced over the next five years. Other studies have suggested that diets high in lutein and zeaxanthin (substances found in vegetables such as broccoli, Brussels sprouts, and spinach) and omega-3 fatty acids might help slow the progress of AMD. However, those studies only suggested a possible link, and couldn’t say for sure whether that link was real.
The researchers in the new study conducted a more accurate type of trial to see if lutein, zeaxanthin (pronounced zee-ah-zan-thin), and omega-3 fatty acids really do slow the progress of AMD. To do this, they followed a group of 4,203 people with AMD who were thought to be at high risk of the condition becoming advanced.
The people were randomly allocated to one of four groups. All of the groups were also given a daily supplement containing vitamin C, vitamin E, beta carotene, zinc, and copper, because this combination of vitamins and minerals has already been shown to slow the progress of AMD. In addition, each group had to take a daily supplement of either:
- lutein and zeaxanthin
- omega-3 fatty acids
- lutein, zeaxanthin, and omega-3 fatty acids
- placebo (dummy pill)
In each group, the researchers recorded the number of eyes (not all people get AMD in both eyes) that developed advanced AMD over a five-year period.
The researchers were trying to discover if lutein, zeaxanthin, and omega-3 fatty acids provided extra protection.
What does the new study say?
The researchers found that people in all the groups had just under a one-in-three chance of developing advanced AMD over five years. So, regardless of whether people took an additional placebo or an additional combination of supplements, the risk of developing advanced AMD remained the same. In other words, the additional supplements didn’t seem to have any effect on the disease. One analysis suggested people who might benefit from the supplements were those whose diet usually contained very little lutein and zeaxanthin.
How reliable is the research?
This is a well-designed study where a large group of people were randomly given different treatments. Neither the researchers nor people in the study knew which supplements they were getting, so their expectations about which supplements might work, and which might not, couldn’t affect the results.
These sorts of studies (randomised controlled trials) are the best way to find out if one thing causes another. A weakness of the trial is that the people in the study were not very diverse (96% were white). It is not clear whether the results would be the same for different ethnic groups.