Vitamin D and Its Effects on Eyesight

It has been estimated that the complex system that enables eyesight requires about 30 percent of a person's oxygen intake and 25 percent of their nutritional intake. Thus, healthy eyesight depends on essential nutrients, such as vitamins. Vitamins A, C and E are antioxidants that have been well-established as preserving eyesight and promoting healthy eyes, but evidence suggests vitamin D is associated with reduced risks of macular degeneration.

An eye doctor trying glasses on a patient. (Image: Jose Luis Pelaez Inc/Blend Images/Getty Images)

Macular Degeneration

Macular degeneration is a condition that leads to the loss of a person's central field of vision as a result of a degenerating macula, the small region within the retina where vision is sharpest. It is widely recognized as the leading cause of adult irreversible vision loss in developed countries. Macular degeneration doesn't lead to complete blindness, as peripheral vision is unaffected. The National Eye Institute states about 9 million Americans over the age of 40 suffer from macular degeneration.

Vitamin D and Macular Degeneration

A study published in April 2011 in the "Archives of Ophthalmology" found that people who ate more foods with vitamin D, or who took vitamin D supplements, were less likely to develop age-related macular degeneration. Specifically, researchers measured blood levels of vitamin D in 1,313 women under the age of 75 and found that higher levels of vitamin D were associated with a 59 percent reduced risk of developing early macular degeneration.

Vitamin D Deficiency

According to the Office of Dietary Supplements, serum concentration of calcidiol is the best indication of vitamin D status, and levels below 37.5 nanomoles per liter are considered deficient. The recommended daily amounts for vitamin D are 400 international units for infants, whereas most adults require 600 to 700 IU depending on age. Vitamin D is fat soluble and stored in the body for long periods, so deficiency symptoms can take many months to manifest, or years, as is the case with macular degeneration.

Deficiency Symptoms

Common initial vitamin D deficiency symptoms include severe fatigue, profuse sweating, muscle aches, bone pain and depression. Muscle weakness eventually develops with long-term deficiency, which can affect the small muscles of the eye responsible for focusing the lens, as cited in "Vitamins: Fundamental Aspects in Nutrition and Health." Consequently, blurry vision is possible with chronic lack of vitamin D. Other deficiency-related symptoms that could affect eyesight include reduced immunity and higher risks of infection, hypertension and Type 2 diabetes, which could both lead to blood vessel damage to the small arteries supplying blood to the eye.

Vitamin D Sources

The best source of vitamin D is the sun, which triggers the synthesis of it within skin. Certain frequencies of UVB radiation are required, though, which occur only seasonally in most regions in the United States. Vitamin D is not especially prevalent in foods, but good sources include milk, fish and fortified margarines, cereals and juices.

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