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Vitamin D and Eyesight: What You Need to Know

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You’ve probably heard that you can get vitamin D by going out into the sun. And that during the winter months, you may have to take a vitamin D supplement.

But is vitamin D good for the eyes? And if yes, just how good?

In this post, we explore the link between vitamin D and eye health. We’ll see how vitamin D was discovered and review Vitamin D deficiency and eye problems.

We’ll also look at the recommended vitamin D daily dose and whether you need to take a supplement.

Let’s start with the story of vitamin D’s discovery.

How Was Vitamin D Discovered?

The discovery of vitamin D began with the quest to cure rickets. Rickets is a disease that affects bone development in children, causing bone pain, stunted growth, and weak bones that can lead to deformities. It can also affect adults in the form of osteomalacia.

It was a rare condition in the 1600s, but by the late 1700s, it became a major problem in Europe. It was especially common in large cities, where people were living mostly indoors.

In the late 19th century, scientists began searching for foods that could prevent the disease. By then, citrus fruits rich in vitamin C and rice bran rich in vitamin B1 had been found to cure scurvy and beriberi respectively. Scientists supposed that rickets too may be a deficiency disease.

In the 1920s, American researcher Elmer McCollum, who had previously discovered vitamin A, found that rats fed a plain cereal diet went on to develop rickets. Meanwhile, British doctor Edward Mellanby realized that dogs fed cod liver oil didn’t develop the condition, and he assumed vitamin A could prevent the disease.

But in 1922, when McCollum gave sick dogs cod liver oil from which he had destroyed the vitamin A content, it cured their rickets. He identified a compound in the modified cod liver oil that cured the dogs and named it vitamin D because by then three other vitamins had been discovered, vitamins A, B1, and C.

In the following years, researchers realized that exposure to sunlight could also cure rickets. When exposed to the sun, the body produces vitamin D from cholesterol in the skin. No wonder that today vitamin D is called the sunshine vitamin.

What Is Vitamin D?

Vitamin D is a fat-soluble steroid hormone that the body produces from cholesterol when you are exposed to the sun and then stores it in adipose tissue. It’s also available through a few foods. Dietary vitamin D comes in two main forms:

  • Vitamin D2 or ergocalciferol – It occurs in mushrooms exposed to UV light, yeasts, and some plants.
  • Vitamin D3 or cholecalciferol – The more potent version of the vitamin, it occurs in fatty fish, eggs, and a few other animal foods.

brown mushrooms growing in the sun among grass

In the body, the liver converts the vitamin into a form suitable for storage, after which the kidneys help the liver to convert it into an active form. The active form of the vitamin binds to receptors found throughout body cells, activating or deactivating genes.

Your body needs vitamin D to build and maintain bone. It can only absorb calcium, the main constituent of bone, if there is enough vitamin D.

Vitamin D regulates many cellular functions and has antioxidant, neuroprotective, and anti-inflammatory effects. Your muscles, immune system, and brain all need vitamin D to function normally.

Vitamin D and Eyesight

Vitamin D is an important vitamin for the eyes. Its cell-regulating functions, together with its antioxidant and anti-inflammatory benefits, sustain the normal functioning of the eyes. Vitamin D deficiency and vision problems are well established.

A 2014 study found that myopia is more prevalent in individuals with lower vitamin D serum levels. More research is needed to understand why this happens, but time spent outdoors in the sun protects children against myopia, possibly through the effects of vitamin D.

Vitamin D deficiency has been associated with retinopathy in young people with type 1 diabetes. It may also be a risk factor for dry eye disease, according to a 2020 review and meta-analysis. Studies indicate that patients with lower-than-normal levels of vitamin D have worse eye symptoms and lower tear production.

If you have dry eyes, taking a vitamin D supplement may reduce eye inflammation according to a 2020 study. A previous study found that participants who took vitamin D orally saw an improvement in dry eye symptoms and tear quality. However, more research is needed to determine how much vitamin D someone with dry eyes should take, or what is the best mode of delivering it.

Vitamin D may protect against age-related macular degeneration, a major cause of vision loss in both Canada and the United States. This may occur because of the vitamin’s anti-inflammatory benefits.

closeup of woman's brown eye with lighted iris and shadows on the skin

There may also be a link between vitamin D and eye pressure. A 2016 study on 123,331 subjects older than 20 years associated low vitamin D levels with a higher risk of glaucoma in females. Glaucoma occurs because of fluid buildup in the eye, which increases eye pressure and damages the optic nerve.

Other studies found no clear link between vitamin D and eye pressure. More research is needed to understand whether this vitamin can help prevent or treat glaucoma.

In addition to its potential to ward off eye disease, an adequate intake of vitamin D may reduce the risk of diabetes, cardiovascular disease, inflammatory diseases, and other conditions that may result in complications affecting the eyes.

How Much Vitamin D3 Should I Take Daily?

The US National Institutes of Health recommend the following daily vitamin D intake from all sources:

  • Adult males and females between 18 and 70 years, including pregnant women – 600 IU (15 mcg)
  • Senior citizens over 70 years – 800 IU (20 mcg)
  • Children between 1 and 13 years – 400 IU (10 mcg)
  • Infants – 400 IU (10 mcg)

Claims that vitamin D improves eyesight if you take it in large quantities are unfounded. Stick to the recommended vitamin D daily dose to avoid toxicity symptoms.

How Much Vitamin D Is Too Much?

According to most sources, 4,000 IU per day is the upper limit for vitamin D intake. The body doesn’t easily flush out vitamin D, which can accumulate in the body. Too much vitamin D causes in turn a buildup of calcium. Known as hypercalcemia, this causes a host of unpleasant symptoms:

  • Loss of appetite
  • Thirst
  • Dizziness
  • Fatigue
  • Nausea
  • Headaches
  • Depression
  • Memory problems
  • Tiredness

Other symptoms of vitamin D toxicity can include dehydration, constipation, disorientation, frequent urination, high blood pressure, muscle weakness, bone problems, kidney stones, and irritability. If you take a vitamin D overdose, blurry vision may also follow.

Good to know: Vitamin D supplementation may interact with cholesterol-lowering drugs, weight-loss drugs, and stimulant laxatives, reducing the absorption of the vitamin. Also, taking blood pressure drugs with vitamin D may increase the risk of hypercalcemia.

Foods Rich in Vitamin D

Unlike other vitamins, vitamin D is not present in substantial quantities in many foods. The best food sources of this vitamin are:

  • Cod liver oil
  • Rainbow trout
  • Sockeye salmon
  • White mushrooms exposed to UV light
  • Milk and other plant-based drinks fortified with vitamin D
  • Cereals fortified with vitamin D

fish oil capsules scattered on lightly colored background

Sardines, eggs, liver beef, tuna, and cheese have only negligible amounts of vitamin D.

Should You Take a Vitamin D Supplement?

The body can store vitamin D for weeks or months at a time. However, you have to expose a large part of your body to the sun to generate it. Sunscreen will limit how much vitamin D your body can produce, though it’s recommended if you expose yourself to the sun for longer than 10 to 30 minutes.

Getting your vitamin D levels checked is a safe approach to understanding whether you need to take vitamin D supplements. The test can also be an indicator of osteoporosis.

During a vitamin D test, doctors take a blood sample and measure the levels of 25-hydroxyvitamin D or calcidiol, the active form of vitamin D in your body.

Readings of calcidiol below 50 nmol/L (20 ng/mL) may indicate a vitamin D deficiency while readings above 125 nmol/L (50 ng/mL) show higher levels than normal. Note that vitamin D levels may drop during the colder months due to limited sun exposure, so it may be necessary to repeat the test come winter.

overcast old city center street with blurry people in foreground and old buildings to the sides

Vitamin D deficiency is a major problem even in developed countries. Urbanization, long hours at the office, and high digital screen time, which limits time spent outdoors only contribute to the problem. A 2010 study suggests that up to 41.6% of Americans don’t get enough vitamin D.

Post-menopausal women, people with limited sun exposure, people with dark skin, obese people, older adults, and breastfed infants are especially at risk of not getting in enough vitamin D. All these groups may need to take a supplement to meet the recommended dose of vitamin D.

If you belong to one of these groups, discuss with your doctor vitamin D supplementation especially during the winter months when you may not get enough sun exposure.

Good to know: Vitamin D supplements often also include calcium since this vitamin helps your body absorb calcium. A 2021 study found that calcium supplements increase by around 15% the risk of cardiovascular disease in healthy postmenopausal women. It appears to be safer to get your calcium through your diet and take a standalone vitamin D supplement unless advised otherwise by your doctor.

Keeping Your Eyes Healthy

Ensuring that you get enough vitamin D through your diet or, if necessary, through supplements, helps keep your eyes healthy. Vitamin D and eyesight are closely connected. But don’t forget about the other essential vitamins and nutrients your eyes need to work at their best.

Another way to support eye health is to take a full-spectrum vision supplement like SightC. SightC is packed with antioxidants and phytonutrients that protect your eyes against oxidative damage, inflammation, and common eye diseases. It’s a natural supplement that brings together the wisdom of goji berries, turmeric, Cherokee rose, and other plants.

Through its lutein, zeaxanthin, and other nutrient content, SightC can help relieve dry eyes and provide nutritional support for age-related macular degeneration, glaucoma, and other eye illnesses.

Keep your eyes heathy and happy with SightC.

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