“Eat your carrots – they’re good for your eyes.” You probably heard that more than once as a child. Maybe you even ate extra servings - trusting they’d keep you from needing glasses.
Actually, it’s not just a ploy to get stubborn kids to eat their vegetables. Carrots may not guarantee 20/20 vision, but they do have nutrients like beta-carotene, which is converted by the body into vitamin A – essential to eye health (1). Beta-carotene is also in other orange foods: yams, papayas, mangoes, etc (2) and green leafy produce including spinach and kale (2). Vitamin A and other “antioxidant” vitamins including C and E and minerals such as selenium and zinc, help counteract the processes that lead to vision impairment and other medical issues. That’s why nutritionists champion these fruits and vegetables as part of a healthy diet (2).
Now vitamin supplements containing high concentrations of antioxidants are increasingly being marketed for their benefits in preventing age-related eye disease, specifically cataract and macular degeneration (AMD) (6;7). These eye diseases commonly develop with age and can lead to serious consequences, including vision loss (2;3).
While we’d like it to be true, do these vitamins really help prevent or slow the progress of aging-related vision problems or are they a waste of money?
Fortunately, researchers wanted answers to these same questions and carried out studies to find out if consumption of antioxidant vitamins have any impact on the development of cataracts or AMD. Some of those studies were included in three well-done systematic reviews: one on cataracts including nine randomized controlled trials and more than 117,000 participants (6); and another two on AMD including a combined 24 randomized controlled trials and more than 80,000 participants (7;8). Those in the study groups were given antioxidant vitamin supplements including beta-carotene, vitamin C, vitamin E, lutein, and zinc. Researchers measured the number of people who developed cataracts or AMD and compared this to control groups who were given placebos or no supplements. These trials ranged from six months to 12 years in duration (6-8).
What the research tells us
The results were consistent and conclusive: taking antioxidant vitamins – single vitamins or in combination – does not help prevent either age-related cataracts or AMD (6;7). However, in those with AMD, antioxidant vitamin and mineral supplementation may slow down the progression of the disease, particularly in people at high risk of having progression occur—like those with moderately severe AMD. It’s important to note that this potentially positive outcome was seen in an American population that was considered to be well-nourished. So, whether this finding can be applied to various populations still requires more precise and direct research (8).
There were no serious vision-related side effects from taking supplements, but a significant percentage (7% to 16%) of people taking beta-carotene as part of the cataract studies experienced “hypercarotenodermia,” yellowing of the skin (6). The AMD review cautioned against high dose supplements as not enough is known about their impact; for example two of the included trials noted a slightly higher risk of lung cancer in the study participants (7).
So there we have it: vitamin supplements likely won’t help you avoid these eye diseases and may possibly cause harm. But as the review authors hasten to add: keep eating your coloured vegetables! The recommended daily allowances of antioxidant vitamins and minerals that we get through healthy foods can still help to keep our eyes – and the rest of our bodies – functioning well for as long as possible (6).