Vitamin A beneficial for eyes, just not for preventing myopia

Sorry, carrot proponents-while vitamin A is responsible for myriad ocular health benefits, especially protecting against childhood blindness, it doesn't appear to stem myopia progression in youth.

Published in the journal Translational Vision Science & Technology, a recent Australian study found no evidence that young adults with low vitamin A intake are likely to become myopic by age 20; however, while not linear, there may be a threshold for optimal vitamin A intake and axial elongation. The evidence comes as greater attention is paid to the burgeoning myopia epidemic globally and clinical methods with which to slow or prevent myopia progression.  

A group of antioxidants, vitamin A not only is beneficial to a healthy functioning ocular surface but also is required for the formation of the photoreceptor rhodopsin. This photopigment found in rod cells of the retina is especially helpful in allowing our eyes to see at night. Therefore, night blindness is often one of the first signs of vitamin A deficiency.  

Although rare in the United States due to a sufficient diet and nutrient intake, vitamin A deficiency is the leading cause of preventable blindness in children with an estimated 250,000-500,000 children worldwide going blind every year. While insufficient vitamin A is known to negatively affect eye health, researchers sought to examine any links that implicate vitamin A deficiency with myopia progression.  

Per the study, researchers performed a prospective analysis with data from 642 subjects, including dietary vitamin A intake determined by food questionnaires at ages 14, 17 and 20. That data was then compared to ophthalmic measurements collected when subjects turned 20 years old. A total of 158 subjects had myopia (24.6%) at the start of the study.  

In defining low vitamin A intake as less than 600 µg per day for both males and females, researchers identified 37 subjects (5.8%) with low vitamin A intake at year 14; 107 subjects (16.7%) at year 17; and 445 subjects (69.3%) at year 20. Of those 37 subjects with low vitamin A intake at 14 years, 11 had myopia (29.7%), while of the 107 subjects at year 17, 25 had myopia (23.4%), and of the 445 subjects at year 20, 122 (27.4%) had myopia.  

"Despite our analysis demonstrating no association between myopia and vitamin A intake with data from the selected cohort, we believe that there is a theoretical association between myopia and vitamin A," authors note.  

In supporting that assessment, researchers noted how animal studies suggest dopamine affects eye elongation and dopamine has been shown to be "released by bipolar cells to modulate layers of the retina by a synaptic or volume transmission." Additionally, some genes have been identified in association with myopia and various genetic pathways implicated in refractive errors, prompting researchers to suggest vitamin A insufficiency may be such a pathway. Finally, they posit another potential pathway "supporting the association between vitamin A and myopia is the relationship between retinitis pigmentosa and myopia."  

Authors concluded: "We found no evidence that young adults with low vitamin A intakes are likely to have myopia at 20 years of age. Although the link between myopia and vitamin A does not appear to be linear, a threshold may exist for optimal vitamin A intake and axial elongation."  

Nutrition and eye health  

Regular, comprehensive eye care is often patients' primary entry point into the health care system, emphasizing the influence that doctors of optometry have on overall patient health. However brief, this chair time affords doctors of optometry an opportunity to reinforce proper nutrition for not only reduction of vision loss risk but also prevention of chronic conditions.  

Consider these daily recommended values for eye-friendly nutrient consumption:

Vitamin A
400-700 mcg Retinol Activity Equivalents

Vitamin A supports functioning of the conjunctival membranes and cornea.

Lutein & zeaxanthin
10 mg/day lutein

2 mg/day zeaxanthin Lutein and zeaxanthin, carotenoids, help neutralize oxidative damage as well as filter high-energy blue light reaching the eye, in turn reducing the risk of AMD and cataracts.

Vitamin C
500 mg/day

Vitamin C, ascorbic acid, promotes healthy blood vessels and helps neutralize oxidative damage that can lead to cataract development or AMD progression.

Vitamin E
400 IU/day

Vitamin E helps neutralize oxidative damage, in turn helping reduce AMD progression and cataract formation.

Zinc
11 mg/day for men
8 mg/day for women
80 mg/day for high risk of AMD

Zinc helps vitamin A produce melanin to protect the eye and may help delay AMD progression, while a zinc deficiency also has been linked to poor night vision.

Essential Fatty Acids
1 g/day of EPA + DHA

Omega-3 fatty acids, particularly DHA and EPA, promote visual development and healthy retinal function, while an omega-3 deficiency may be linked to dry eye.

For more about nutrition and the role of supplements in eye care, AOA members can read the "Eating for Your Eyes" feature in the November/December 2019 edition of AOA Focus.