Vitamin D and eye health


Vitamin D is crucial for healthy bones and teeth due to the fact that it helps the body absorb calcium and phosphorus. However, there is significant evidence that the sunshine vitamin is also actively involved in regulating immunity. Thus, it helps your body to fight infectious disease, reduces the severity of asthma and allergies, and lowers the risk of autoimmune disorders.

Emerging research has also found a close link between vitamin D deficiency and conditions like cardiovascular disease, cancer, diabetes, and complications associated with diabetes.

In this blog, we discuss why and how Vitamin D is an important factor in eye health.

Vitamin D’s anti-inflammatory properties, along with many other benefits, may help in reducing the risk of all kinds of eye diseases such as age-related macular degeneration, diabetic retinopathy, myopia (near-sightedness) and dry eye syndrome.More importantly, Vitamin D deficiency and eye problems are closely related, as low D levels have been implicated with a higher risk of developing the aforementioned conditions.

The big questions remain: what exactly is the connection between Vitamin D and eye health? Can a lack of vitamin D cause eye problems?

Let’s find out.

1. Vitamin D and macular degeneration

Macular degeneration is the leading cause of vision loss in the elderly. In this condition, the macula – a small spot in the centre of the retina – is damaged. It is also called age-related macular degeneration (AMD).

The macula is made of millions of light-sensitive cells (rods and cones), which are responsible for sharp, detailed vision along with central vision. Damaged macula results in blurry or distorted central vision. This impacts your ability to perform simple day to day activities like reading, writing, driving, cooking, and recognizing faces. AMD also reduces your ability to see colors.

In order to understand the connection between Vitamin D and eye health, it is important to understand various stages of AMD:

Early AMD
  • Marked by the presence of small or medium-sized drusen – round yellow. deposits of fats and proteins that build up in the eye.
  • Does not cause any symptoms or vision loss.
  • If left undiagnosed and untreated, it progresses into a more advanced form, leading to blurred or distorted vision.
Intermediate AMD
  • Number and size of drusen increases.
  • Symptoms are noticeable and include blurred spots in the central vision and a need for more light.
  • Larger drusen size increases the risk of developing Wet Macular Degeneration, a more advanced form that can lead to a sudden loss of central vision.
Drusen clog the supply of oxygen and nutrients to the macula. These spots also interfere with the elimination of waste products, causing deterioration and death of Retinal Pigment Epithelial Cells.

Late AMD
  • Marked by a gradual breakdown of the light-sensitive cells in the macula and supporting tissue. The blurred spot in the central vision becomes bigger and darker, potentially leading to loss of vision over time. This is called Dry AMD and is what the majority of patients are diagnosed with.
  • For some people, Dry AMD may progress into a more advanced form of AMD, which is marked by the growth of new blood vessels (angiogenesis) and scarring of retinal tissue (fibrosis). This is called Wet AMD. Vision loss caused by such damage is permanent and can no longer be reversed with surgery or injections. Symptoms include blurred vision and the presence of grey spots in the central field of view. People with Wet AMD also find that straight lines seem wavy or curvy.
In an attempt to improve the supply of oxygen and nutrient-rich blood to the retina, new blood vessels begin to grow. However, these fragile new blood vessels leak blood and fluid, causing severe damage to the retinal cells. This process also causes scarring of the retinal tissue. Also, the fluid build-up causes the macula to raise and bulge, which is why sudden and more severe changes in vision are often experienced.

While age, genetics, and environmental factors like smoking are involved in the development of AMD, recent research suggests that inflammation may play a big role in its development. Inflammatory molecules have been found within drusen, supporting the central role of inflammation.

Studies show that low levels of vitamin D increase one’s risk of early and/or late AMD. [1] [2] Also, vitamin D is believed to play a tremendous role in fighting inflammation, oxidative damage, angiogenesis (growth of new blood vessels), and fibrosis. These properties may help in preventing the development and progression of AMD. [3] [4] [5]. Further, a 2015 study suggested that maintaining healthy vitamin D levels may help to reduce some of the risk in those who are genetically prone to develop macular degeneration. [6]

Unfortunately, AMD is incurable. Since people typically don’t experience any vision loss initially, it is important to follow a regular eye exam schedule. This is especially important if you are at risk.

2. Vitamin D and diabetic retinopathy

People with diabetes are at an increased risk of developing microvascular complications, such as diabetic retinopathy (DR). In fact, DR is one of the most common complications associated with diabetic patients with poorly controlled blood glucose levels.

If not treated well and in time, it can even lead to blindness.

High blood sugar levels are known to damage tiny blood vessels in the retina. These vessels are responsible for providing retina with oxygen and nutrients.

  • In the initial stages of diabetic retinopathy, these tiny blood vessels develop small areas of swelling, making them prone to leaking fluid in the retina.
  • As the disease progresses, the blood vessels begin to swell and lose their ability to supply oxygen-rich blood to the retina.
  • In the later stages, the retina releases growth factors that trigger the formation of abnormal blood vessels. This process is called neovascularization and it is the body’s way of restoring oxygen supply to the retina. However, these fragile new vessels often rupture, leaking blood into the vitreous gel, the fluid that fills the middle of the eye. These dangerous changes within the eye can lead to blurred vision and even complete vision loss if left untreated. This situation can be prevented by controlling blood sugar levels and having your eyes regularly screened.
Growth of new blood vessels and chronic inflammation are two of the most important factors associated with the development of diabetic retinopathy. Vitamin D plays an important role in controlling both inflammation and angiogenesis and appears to be protective against diabetic retinopathy (DR).

What’s more, emerging research shows that low vitamin D status is closely related to DR. [7] A 2017 meta-analysis found that vitamin D deficiency may increase the risk of diabetic retinopathy in patients with type 2 diabetes. [8]

Another study concluded that “A low serum 25-OHD level was an independent predictor of HbA1c, diabetic neuropathy, and diabetic retinopathy in patients with DM2.” [9]

3. Vitamin D and diabetes

Poorly controlled blood glucose levels and high blood pressure are strong risk factors for retinopathy. It is well established that Vitamin D for eye health extends to controlling blood glucose and blood pressure.

A study published in Cardiovascular Diabetology concluded that a healthy vitamin D status (=75 nmol/L) may be effective in reducing the risk of diabetic retinopathy. The researchers speculated that vit D’s ability to regulate blood glucose may be the reason for this effect. [10]

A more recent study suggested that the higher the levels of vitamin D in the blood, the lower the risk of developing diabetes. [11] While this is not the first study to present this association, researchers believe more studies are needed to confirm the role of vitamin D in reducing the risk of diabetes.

A 2018 study found that lower vitamin D levels are associated with higher blood glucose levels in Asian Indian women with pre-diabetes. People with pre-diabetes – with abdominal obesity, insulin resistance, and metabolic syndrome – are at an increased risk of developing type 2 diabetes as well as cardiovascular disease. [12]

Another 2018 meta-analysis concluded that “Vitamin D supplementation and improved vitamin D status improved glycemic measures and insulin sensitivity and may be useful as part of a preventive strategy for type 2 diabetes.” [13]

Diabetic retinopathy may not produce any noticeable symptoms in the early stages. It is, therefore, all the more important to detect the condition early, before it leads to complete loss of vision. Judging by the link between low vitamin D levels and increased risk of DR, screening for D levels may be a useful tool in catching the problem early enough to warrant treatment.

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4. Vitamin D and myopia

People with myopia can see close objects clearly, meaning they can read things up close like a book or computer screen, while further objects appear blurred. Myopia is also known as near-sightedness or short-sightedness.

In this condition, the eye grows too long from front to back. As a result, the rays of light can’t focus properly on the retina – a thin layer of light-sensitive tissue in the back of the eye. Normally, the cornea and lens focus rays of light on the retina, which senses the light and converts it into signals that are carried to the brain. Your brain then interprets these signals as the images you finally see. In myopia, as the eye is too long, the lens focuses light in front of the retina instead of focusing it on the retina.

This results in a blurry image.

Genetics play a major role in myopia. However, certain factors like spending too much time indoors and doing near work can also increase the risk. Therefore, people who read a lot and spend a lot of time on computers or phones are likely to develop myopia.

How is vitamin D deficiency related to myopia?

Low vitamin D levels are associated with an increased risk of myopia, as shown by several studies. [14] So, can playing outdoors help reduce myopia risk?

New research suggests that increased outdoor time can prevent the onset of myopia in young children. There are many theories on why playing outdoors may help. For example, playing in the sunlight helps the body make more vitamin D, which may play a role in preventing abnormal eye growth in children.

Another theory suggests that brighter light is the key element. Brighter light outdoors stimulates the cells in the retina to release dopamine, helping with slower, more normal eye growth. [15]

Another study showed that myopic children spent more time indoors, had lower D status, had a higher body mass index, and played fewer sports than children who didn’t have myopia. [16]

This 2016 study showed that low vitamin D levels in the blood were linked with longer axial length and increased risk of myopia in a group of 6-year-old children. Interestingly, this effect was found to be unrelated to outdoor exposure, suggesting that a lack of vitamin D may have a direct role in the development of myopia. [17]

5. Vitamin D and dry eye

Dry eye is a condition where your eyes do not produce sufficient moisture or tears as normally, when you blink, a layer of tears spreads over the cornea – the surface of your eye. Tears keep the eye’s surface moist and also wash away any dust or micro-organisms that could increase the risk of eye infections. You need a healthy layer of tears at all times to ensure healthy eyes and clear vision.

If you have symptoms like dryness, redness, a burning sensation in the eyes, increased sensitivity to light, and blurred vision, chances are you may have dry eyes. Another important symptom of dry eye syndrome (which you should pay attention to) is if your eyes are becoming tired at a faster pace than previously.

Many recent studies have suggested that vit D deficiency may cause dry eye syndrome. [18] [19] [20] [21] Since inflammation is often the underlying cause of dry eyes, this association makes sense. Studies show that low D levels may cause dry eye and impaired tear function [22]. Plus, this same study further reported that vitamin D may play a protective role against dry eye syndrome due to its ability to reduce inflammation as well as enhance tear film functions. [23]

A 2016 study concluded that vitamin D supplementation is an effective strategy for patients with dry eye syndrome who are not responding to conventional treatment. [24]

The study reported that vitamin D supplementation:

  • Stimulated the secretion of tears
  • Reduced tear instability
  • Lowered inflammation
  • Improved the symptoms of dry eye syndrome

References:
  1. Millen et al. Vitamin D status and early age-related macular degeneration in postmenopausal women. Arch Ophthalmol. 2011
  2. Morrison et al. Systems biology-based analysis implicates a novel role for vitamin D metabolism in the pathogenesis of age-related macular degeneration. Hum Genomics. 2011
  3. Layana et al. Vitamin D and Age-Related Macular Degeneration. Nutrients. 2017
  4. Lee et al. Vitamin D rejuvenates aging eyes by reducing inflammation, clearing amyloid beta and improving visual function. Neurobiology of Aging. 2012
  5. Jin et al. Chapter 34 - Vitamin D and Age-Related Macular Degeneration. Handbook of Nutrition, Diet and the Eye. 2014.
  6. Millen et al. Association between vitamin D status and age-related macular degeneration by genetic risk. JAMA Ophthalmol. 2015
  7. Zhang et al. Relationship between vitamin D deficiency and diabetic retinopathy: a meta-analysis. Can J Ophthalmol. 2017
  8. Luo et al. The Association between Vitamin D Deficiency and Diabetic Retinopathy in Type 2 Diabetes: A Meta-Analysis of Observational Studies. Nutrients. 2017
  9. Ahmadieh et al. Hypovitaminosis D in Patients with Type 2 Diabetes Mellitus: A Relation to Disease Control and Complications. ISRN Endocrinol. 2013
  10. Millen et al. Adequate vitamin D status is associated with the reduced odds of prevalent diabetic retinopathy in African Americans and Caucasians. Cardiovascular Diabetology 2016
  11. Park et al. Plasma 25-hydroxyvitamin D concentration and risk of type 2 diabetes and pre-diabetes: 12-year cohort study. PloS One. 2018.
  12. Bhatt et al. Lower vitamin D levels are associated with higher blood glucose levels in Asian Indian women with pre-diabetes: a population-based cross-sectional study in North India. BMJ Open Diabetes Research & Care. 2018.
  13. Mirhosseini et al. Vitamin D Supplementation, Glycemic Control, and Insulin Resistance in Prediabetics: A Meta-Analysis. Journal of the Endocrine Society, Volume 2, Issue 7, 2018.
  14. Choi et al. Low serum 25-hydroxyvitamin D is associated with myopia in Korean adolescents. Invest Ophthalmol Vis Sci. 2014
  15. Kwon et al. Serum 25-hydroxyvitamin D level is associated with myopia in the Korea national health and nutrition examination survey. Medicine (Baltimore). 2016
  16. K.M Williams et al. Association Between Myopia, Ultraviolet B Radiation Exposure, Serum Vitamin D Concentrations, and Genetic Polymorphisms in Vitamin D Metabolic Pathways in a Multicountry European Study. JAMA Ophthalmol. 2017
  17. Tideman et al. Low serum vitamin D is associated with axial length and risk of myopia in young children. Eur J Epidemiol. 2016
  18. Galor A. et al. . Effect of a Mediterranean dietary pattern and vitamin D levels on Dry Eye syndrome. Cornea. 2014.
  19. Kurtul et al. The association of vitamin D deficiency with tear break-up time and Schirmer testing in non-Sjögrendry eye. Eye (Lond). 2015.
  20. Demirci et al. Patients with vitamin D deficiency may be prone to dry eye. Dry Eye Assessment in Patients With Vitamin D Deficiency. Eye & Contact Lens. 2016.
  21. Yoon S. Y. et al. Low serum 25-hydroxyvitamin D levels are associated with dry eye syndrome. PLoS One. 2016.
  22. JIn et al. Correlation of vitamin D levels with tear film stability and secretion in patients with dry eye syndrome. Acta Ophthalmol. 2017
  23. Yildirim et al. Dry eye in vitamin D deficiency: more than an incidental association. International Journal of Rheumatic Diseases. 2015.
  24. Bae et al. Vitamin D Supplementation for Patients with Dry Eye Syndrome Refractory to Conventional Treatment. Sci Rep. 2016