If you want to preserve your vision as you age, you might consider tossing your vitamin C supplement. According to a study published in the February issue of the American Journal of Clinical Nutrition, high-dose vitamin C supplements - 1,000 milligrams daily - can increase the risk of developing cataracts.
Researchers followed 25,593 women, aged 49 to 83, for eight years and found that those who took 1,000 mg of vitamin C daily were 25 per cent more likely to develop cataracts than those who did not use supplements.
Among women 65 and older, vitamin C use increased the risk of cataract by 38 per cent. Taking vitamin C in combination with hormone replacement therapy or corticosteroid medication was associated with an even greater risk.
However, getting too little vitamin C may also contribute to cataracts, since vitamin C is a potent antioxidant, protecting from free radicals. Previous research has linked higher blood levels and dietary intakes of vitamin C with a lower risk of cataracts.
The new study showed that multivitamins containing a small amount of vitamin C (60 mg) did not increase cataract risk.
A cataract is a clouding of the lens of the eye, which focuses light onto the retina at the back of the eye. When the lens is cloudy, the light is obstructed, affecting vision.
It's thought that free radicals play a role in cataract development by damaging proteins in the lens. Free radicals are produced naturally when we breathe, but ultraviolet light, cigarette smoking and the consumption of alcohol are other sources.
People can develop cataracts in their 40s and 50s, but they're most common after age 65. Family history, diabetes, exposure to sunlight, smoking and alcohol consumption also increase the risk.
This isn't the first study to suggest that high-dose vitamin C supplements may harm your eyes. An earlier, 12-year study of 47,000 U.S. women revealed that long-term vitamin C users aged 60 and older were more likely to have surgery to remove cataracts and were twice as likely to develop cataracts.
It may seem paradoxical that vitamin C, a powerful antioxidant, contributes to cataract. Scientists believe that, under certain conditions, vitamin C can also act as a "pro-oxidant." In other words, the nutrient has antioxidant activity when it reacts with free radicals, but it can also react with other compounds in cells, which leads to the formation of free radicals.
In this study, taking 1,000 mg of vitamin C daily increased the risk of cataract. But the risk was even higher in older women, those using hormone replacement therapy, and those taking corticosteroids (used to treat many conditions including allergy, asthma, arthritis, and inflammatory bowel disease). It's thought that the combination of these factors may increase inflammation in the body and free radical production.
These findings should not be translated to vitamin C from foods. Eating at least seven daily servings of fruit and vegetables - about 3.5 cups worth - is an important way to meet daily vitamin C requirements. Women and men require 75 and 90 mg respectively; smokers need an additional 35 mg a day because smoking creates free-radical damage.
When it comes to nutrition, evidence suggests the following strategies may shield your eyes from cataracts.
Control your weight
People who are overweight, even moderately, have a higher risk of cataracts. Excess body fat around the abdomen may contribute to cataract formation by increasing inflammation in the body. Carrying excess weight also increases the risk of type 2 diabetes, a condition strongly related to early cataract formation.
Choose low-glycemic carbs
A diet of predominantly high-glycemic carbohydrates (e.g. white bread, white rice, sugary foods) is thought to increase the risk of developing cataracts by elevating blood glucose. Prolonged high blood glucose levels in the lens may increase cataract risk by causing free radical damage to lens proteins.
Choose foods that have a low glycemic index such as whole-grain breads, brown rice, pasta, steel-cut oats, legumes, nuts, citrus fruit, yogurt, milk and soy beverages.
A handful of studies suggest omega-3s from fish oil, called DHA and EPA, protect from cataracts by helping fight inflammation in the body.
To increase your intake of omega-3 fatty acids, eat oily fish such as salmon, trout, sardines and herring at least twice a week. If you don't like fish, consider taking a fish oil capsule that supplies 500 to 600 mg of DHA and EPA (combined).
Increase fruits and vegetables
These foods contain two natural compounds called lutein and zeaxanthin. Once consumed, they make their way to the eyes where they act as antioxidants and protect the lens from oxidative damage. Studies show that people who consume the most lutein have a 20-per-cent to 50-per-cent lower risk of developing cataracts or having cataract surgery compared to those who consume the least. Scientists speculate that an intake of six to 15 mg of lutein plus zeaxanthin per day is optimal for eye health. The best sources include kale, Swiss chard, collard greens, green peas, broccoli, romaine lettuce, Brussels sprouts, nectarines and oranges.
Research suggests that a high-sodium diet can increase the risk of cataracts by as much as twofold. Adults require 1,200 to 1,500 mg of sodium a day, half the amount most of us consume. The daily upper limit is 2,300 mg a day. Read nutrition labels and limit your intake of salty snacks and processed meats. Rely less on convenience foods and cook most of your own meals.
Limit or avoid alcohol
Studies show that compared to non-drinkers, daily drinkers have a significantly higher likelihood of cataracts. Alcohol increases free radicals that damage proteins in the lens and may also affect absorption of nutrients.
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.