Salt Damages Vision

Loss of vision and blindness in older Americans is due primarily to macular degeneration, diabetic retinopathy, glaucoma and cataract formation. A diet high in fruits and vegetables, particularly those rich in carotenoids, has been associated with a reduced risk of macular degeneration and cataracts. Cardiovascular risk factors like diabetes, hypercholesterolemia, smoking and hypertension may increase the risk of vision loss due to damage to the eye’s macular and retina.

Diabetic retinopathy progresses much more slowly when blood sugar and blood pressure levels are kept low.1 It seems likely that a DASH-style diet low in salt should help prevent or slow the progression of retinopathy and macular degeneration, the major causes of irreversible blindness of adult Americans.

Cataracts are the most important cause of blindness worldwide but in the US cataract surgery is quite successful at restoring lost vision. Research in animals has shown that a high-salt intake speeds up the formation of cataracts.2 A recent population study conducted in Australia found that those who consumed more salt were twice as likely to have posterior subscapular cataracts, which are the visually most disabling type of cataract.3 The results of this study confirm those of an earlier epidemiological study done in Italy.4

How does too much salt promote cataract formation? Excessive dietary salt, particularly when accompanied by low intakes of potassium, calcium and magnesium creates an electrolyte imbalance in the body. Patients with cataracts have been shown to have higher serum sodium levels control subjects.5 This makes it more difficult for the sodium pumps in cellular membranes to remove excess sodium from inside the cells. A low sodium level is required to maintain the eye lens transparency.

The bottom line: People interested in maintaining their vision into old age should be advised to consume a diet rich in fruits, vegetables, whole grains and nonfat dairy products which is also low in salt.

By Dr. James J Kenney, PhD, FACN

References:

1. Janka HU, et al. IDDM. Diabetes 1989;38:460-4

2. Rodriguez-Sargent C, et al. Invest Opthalmol Vis Sci 1989;30:2356-60

3. Cumming RG, Am J Epidemiol 2000;151:624-6

4. Tanani A, Negri E, La Vecchia C. Ann Epidemiol 1996;6:41-6

5. Miglior S, Marighi PE, Musicco M, et al. Opthalmic Epidemiol 1994;1:93-105

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