Cataracts are a clouding of the lens in the eye that affects vision. They are very common, especially in older adults. Cataracts develop slowly over time and can eventually lead to blindness if left untreated. While cataracts are mostly caused by aging, there are some vitamin deficiencies that can contribute to their formation. The main vitamins that have been implicated in cataract development are vitamins A, C, and E. Deficiencies in these antioxidants allow free radicals to damage lens proteins, leading to clouding and cataracts.
What are cataracts?
Cataracts are a clouding or opacity of the lens in the eye. The lens is normally clear and allows light to pass through it and focus on the retina, allowing us to see. With cataracts, the lens becomes cloudy and prevents light from adequately passing through. This leads to blurred vision, sensitivity to light and glare, double vision in one eye, faded colors, and poor night vision. Cataracts typically develop slowly over a number of years. As they worsen, they can cause vision loss that impairs daily activities and cannot be corrected with prescription glasses or contacts. While they mostly occur in older adults, cataracts can develop in younger people as well, especially if certain risk factors are present.
Types of cataracts
There are several different types of cataracts:
– Nuclear cataracts: Cloudiness forms in the center of the lens, causing yellowing/browning of the lens. This is the most common type of age-related cataract.
– Cortical cataracts: Cloudy streaks develop in the lens cortex (outer edges).
– Posterior subcapsular cataracts: Cloudiness forms at the back of the lens near the capsule. These interfere with near and reading vision.
– Congenital cataracts: Present at birth or develop in early childhood, often requiring surgery.
– Secondary cataracts: Caused by other eye conditions like glaucoma or an injury. Also can be caused by radiation or long-term steroid use.
Causes and risk factors
Age is the most significant risk factor, with most cataracts occurring after age 60. However, there are several other factors that can raise risk for developing cataracts at a younger age, including:
– Ultraviolet light exposure
– Smoking
– Alcohol use
– High blood pressure
– Obesity
– Diabetes
– Prolonged steroid use
– Radiation exposure
– Eye injury or inflammation
– Genetic disorders like Down syndrome
Vitamin deficiencies have also been shown to contribute to cataract formation. The main nutritional risk factors are low levels of vitamin A, C, and E.
How do vitamins A, C, and E prevent cataracts?
Vitamins A, C, and E are all important antioxidants that help prevent cataracts by stopping oxidative damage to the lens. Oxidative stress caused by factors like UV light, smoking, and diabetes generate free radicals that can impair lens proteins. Antioxidants neutralize these free radicals before they can harm the eye.
Vitamin A
Vitamin A (retinol) is essential for eye health and vision. In the eye, vitamin A is converted to retinaldehyde which combines with proteins to form rhodopsin – a pigment necessary for low light and night vision. Retinaldehyde also supports the cornea. Vitamin A deficiency causes dry eyes and blindness from corneal damage, as well as night blindness. Additionally, Vitamin A protects the lens by neutralizing free radicals before they can form cataracts. Low vitamin A status is associated with an increased risk of cataracts. Good food sources of vitamin A include eggs, milk, liver, carrots, spinach, broccoli, and red peppers.
Vitamin C
Vitamin C (ascorbic acid) is a powerful antioxidant that scavenges free radicals and reactive oxygen species (ROS) throughout the body, including in the eye. The lens contains high concentrations of vitamin C which supports redox reactions that prevent oxidative damage to lens proteins. Vitamin C also helps recycle and regenerate other antioxidants like vitamin E. Low levels of vitamin C are linked to a higher risk of cataracts. Fruits and vegetables are excellent sources of vitamin C, including citrus fruits, berries, tomatoes, bell peppers, broccoli, potatoes, and leafy greens.
Vitamin E
Vitamin E refers to several fat-soluble compounds known as tocopherols and tocotrienols which have strong antioxidant abilities. Vitamin E protects cell membranes from peroxidation and oxidative damage caused by free radicals. It is the main antioxidant located in the lipid-rich cell membranes of the eye which protects the lens from oxidation. Low plasma levels of vitamin E are associated with increased cataract risk. Good dietary sources of vitamin E include nuts, seeds, wheat germ oil, sunflower oil, spinach, broccoli, avocado, shrimp, rainbow trout, and olive oil.
Observational studies on vitamin intake and cataracts
Numerous observational studies have found links between inadequate intake of vitamins A, C, and E and increased risk of cataracts:
– A study in over 50,000 U.S. male health professionals found that men in the highest quintile for vitamin C intake had a 33% lower risk of cataracts compared to men in the lowest quintile. Men with high intakes of vitamins A and E also had lower cataract risk.
– An Australian study of over 900 older adults found that those with the highest plasma concentration of vitamin E had 48% fewer cataracts. Higher plasma vitamin C was also protective.
– In a cohort of Swedish women, high dietary intake of vitamins C and E was associated with significantly decreased incidence and progression of lens opacities and cataracts over 10 years.
– Italian researchers found that older adults with low blood levels of vitamins A and E had 5X higher risk of developing cataracts over 6 years compared to those with adequate status.
– Several studies in India, where vitamin A deficiency is common, indicate low vitamin A intake increases cataract risk.
While these observational studies show strong associations, randomized controlled trials provide more definitive evidence on the efficacy of vitamin supplementation for cataract prevention.
Vitamin trials and cataract treatment
Several randomized controlled trials have tested antioxidant vitamin supplements for preventing or slowing cataract progression with mixed results:
Vitamin A
– A trial in rural Nepal gave 15,000 IU vitamin A weekly for 5 years to school-aged children. Vitamin A supplements reduced the formation of haze and opacity in the eyes by over 50%.
– An Indian trial also found vitamin A deficient children who were supplemented had significantly lower rates of corneal abnormalities and blindness.
Vitamin C and E
– In the Roche European American Cataract Trial (REACT), over 300 adults were randomized to take daily vitamin C (300 mg) and vitamin E (140 IU) supplements or placebo for 3 years. Vitamin supplementation slowed progression of lens opacities by 26% compared to placebo.
– However, other major trials like the Age-Related Eye Disease Study (AREDS) and Physicians’ Health Study did not find a significant effect from vitamin C and E supplementation on cataract risk or progression. The doses used may have been too low.
Multivitamins
– The AREDS trial tested daily antioxidant supplements containing high doses of vitamins C, E, beta-carotene, and zinc. Over 10 years, the supplements reduced cataract surgery by 16%.
– An Italian trial of over 400 adults also found multivitamin supplements containing vitamins A, C, and E significantly slowed cataract progression compared to placebo over 9 years.
Conclusion
In summary, deficiencies in certain key antioxidants like vitamins A, C, and E appear to be linked to increased risk for cataracts, especially age-related cataracts. These vitamins help defend the lens proteins from oxidative damage. However, clinical trials using vitamin supplements to prevent or treat cataracts have had mixed results. High-dose multivitamins may offer modest benefits for slowing cataract progression, but more research is still needed. The best approach is to ensure adequate intake of antioxidant-rich fruits, vegetables, nuts, and seeds to optimize nutritional status. Vitamin supplementation could benefit those at high risk for deficiency. For optimal eye health, make sure your diet provides sufficient vitamins A, C, and E.
| Vitamin | Food sources | RDA |
|---|---|---|
| Vitamin A | Liver, milk, eggs, carrots, spinach | 900 mcg RAE for men 700 mcg RAE for women |
| Vitamin C | Citrus fruits, berries, peppers, broccoli, leafy greens | 90 mg for men 75 mg for women |
| Vitamin E | Nuts, seeds, vegetable oils, spinach, avocado | 15 mg |
Key points
– Vitamin deficiencies, especially vitamins A, C, and E, are linked to increased risk of cataracts. These antioxidant vitamins help prevent oxidative damage to lens proteins.
– While observational studies consistently show people with low vitamin levels are more prone to cataract formation, randomized controlled trials on vitamin supplements have had mixed results.
– High doses of multivitamin supplements may slow progression of existing cataracts. However, research is still ongoing into their efficacy.
– The safest approach to prevent vitamin deficiency cataracts is to eat a diet high in fruits, vegetables, nuts, seeds, eggs, and fish. These provide adequate levels of protective vitamins and antioxidants.
– Individuals at high risk for vitamin deficiencies, such as the elderly, vegetarians, or those with absorption issues, may benefit from a basic multivitamin/mineral supplement.
– If you have cataracts, talk to your eye doctor about options like surgery or prescription eye drops to help improve cloudy vision. Make sure to address any underlying vitamin deficiencies as well.
