The Role of Vitamin D: A Foundation for Eye Health and Well-Being

What is Vitamin D?

Vitamin D, also known as the sunshine vitamin, is a fat-soluble nutrient critical not only for strong bones but also for a resilient immune system, healthy nerves, and optimal visual function. For the body to utilise it, vitamin D must first be converted into a hormone (calcitriol, also known as 1,25-dihydroxyvitamin D) through metabolic processes carried out by the liver and kidneys.

There are two primary forms of Vitamin D:

• Vitamin D2 (ergocalciferol): Found mainly in plant-based foods, fortified products, and vitamin D vegetables and fruits, such as mushrooms exposed to sunlight. However, vitamin D2 is less effective at raising and maintaining vitamin D levels in the body compared to D3.
• Vitamin D3 (cholecalciferol): Produced naturally in the skin through sunlight exposure and present in foods like fatty fish, eggs, and liver. D3 is more bioavailable and effective at increasing vitamin D levels than D2. D3 is typically derived from animal sources like lanolin (from sheep’s wool).

Why Vitamin D Matters for Overall Health

Vitamin D is more than just a vitamin—it’s a powerhouse that supports your body in countless ways. Here’s why getting enough of it is essential for your health and well-being:

• Bone Health and Calcium Absorption: Vitamin D plays a critical role in helping the body absorb calcium and phosphorus from the gut, which strengthens bones and prevents conditions like osteoporosis. Without adequate vitamin D, bones can become brittle and weak, increasing the risk of fractures with age.
• Muscle and Nervous System Function: Vitamin D supports smooth nerve communication by protecting the myelin sheath, which insulates nerve fibres and ensures efficient signal transmission. It also helps regulate muscle contractions, promoting better coordination and preventing muscle weakness.
• Immune System Support: Vitamin D is essential for a well-functioning immune system. It activates key immune cells, like T-cells, which help your body recognize and fight off infections. At the same time, it helps regulate inflammation, ensuring your immune response doesn’t go into overdrive and cause unnecessary harm. Studies suggest that maintaining adequate vitamin D levels may lower your risk of respiratory infections, improve recovery from illnesses, and support long-term immune health.
• Mood and Emotional Well-Being: Vitamin D influences the production of serotonin, a neurotransmitter that promotes emotional well-being and reduces feelings of stress and anxiety. By supporting a balanced emotional state, vitamin D contributes to a calmer, more resilient mindset during challenging times.
• Blood Glucose Regulation: Vitamin D plays a critical role in blood glucose management by improving insulin sensitivity and supporting the function of beta cells in the pancreas, which produce insulin. Research suggests that adequate levels of vitamin D may help lower the risk of type 2 diabetes and improve glucose control in individuals with diabetes. By maintaining balanced blood sugar levels, vitamin D contributes to sustained energy and reduces the risk of complications associated with chronic high blood sugar.
• Cellular Metabolism: Vitamin D supports cellular metabolism by regulating the expression of genes involved in energy production and repair processes. By aiding mitochondrial function, it helps the body maintain optimal energy levels and cellular resilience against stress.

The Impact of Vitamin D Deficiency on Eye Health

Vitamin D deficiency is surprisingly common in Australia. According to the Australian Bureau of Statistics, about 1 in 4 Australians (23%) are deficient in vitamin D, and this number jumps to 1 in 3 (36%) during the winter months when sunlight is scarce. 

Vitamin D deficiency has been linked to several eye conditions, underscoring the importance of vitamin D and eye health. Studies suggest that low levels of vitamin D may contribute to the following common eye problems:

1. Age-Related Macular Degeneration

Age-related macular degeneration affects the macula, the part of the retina responsible for central vision, leading to significant vision decline.

Research shows that vitamin D reduces oxidative stress and inflammation in the retina, potentially protecting against abnormal blood vessel growth, a common cause of macular degeneration.

2. Glaucoma and Optic Nerve Health

Increased eye pressure causes stress to the optic nerve cells, eventually causing vision loss from glaucoma. Although a lack of vitamin D does not cause the eye pressure to increase, vitamin D deficiency has been linked with glaucoma.

When taken with vitamins to reduce eye pressure, the anti-inflammatory effects and cell metabolism support from vitamin D may help to increase the resilience of the optic nerve cells against elevated eye pressure and reduce glaucoma risk.

3. Diabetic Retinopathy

This condition arises from damaged retinal blood vessels due to high blood sugar levels. Vitamin D supports vascular health, reducing inflammation and improving blood sugar regulation. Low levels of vitamin D have been shown to increase the risk of diabetes.

4. Dry Eye Syndrome

Vitamin D deficiency has been linked to reduced tear film stability and tear production, leading to discomfort and dry eyes. Regular vitamin D intake supports tear production by supporting the meibomian glands and reducing inflammation of the ocular surface, helping to stabilise the tear film.

5. Uveitis (Inflammation of the Uvea)

Uveitis, a painful eye condition caused by inflammation, can impair vision if untreated. Vitamin D regulates immune responses, and according to Australian researchers, can reduce the frequency and severity of uveitis flare-ups by preventing excessive inflammation.

How Much Vitamin D Do You Need?

Vitamin D requirements vary by age, with the following daily recommendations:

• Children and adults (19–50 years): 5 micrograms
• Adults (51–70 years): 10 micrograms
• Adults over 70 years: 15 micrograms

These guidelines ensure optimal bone, immune, and nerve health, as well as support for visual health.

Getting Enough Vitamin D

Vitamin D levels are measured in nanomoles per liter (nmol/L) in your blood. Here's a quick guide:

• Optimal: 50–125 nmol/L – This is the sweet spot for maintaining strong bones, a healthy immune system, and overall well-being
• Insufficient: 30–49 nmol/L – Your levels are low, and you may not be getting enough sun exposure, dietary vitamin D, or supplementation
• Deficient: Below 30 nmol/L – This indicates a serious deficiency that can lead to issues like weak bones, muscle pain, and fatigue

A balanced diet, regular sun exposure, and supplements can help keep your vitamin D at optimal levels.

Dietary Sources

Although food can provide some vitamin D, most people struggle to get enough from diet alone. Here are a few sources worth incorporating into your diet:

• Fatty Fish: Salmon, mackerel, and sardines are excellent sources.
• Egg Yolks: A nutritious addition to breakfast.
• Fortified Foods: Many plant-based milks and yogurts are enriched with vitamin D.
• Sun-Exposed Mushrooms: Leaving mushrooms in sunlight for 15 minutes boosts their vitamin D content.

Sunlight Exposure

Since food alone isn’t enough, sunlight is a natural and powerful way to increase vitamin D levels. When ultraviolet B (UVB) rays hit the skin, they trigger production of vitamin D3. However, how much you produce depends on various factors:

• Skin Tone: Darker skin requires more exposure to produce adequate vitamin D.
• Amount of Skin Exposed: The more skin you expose, the better the absorption.
• Season and Location: Sun exposure and UV intensity vary throughout the year. In southern Australia, midday sun exposure during winter is essential to maintain levels.
• Recommended Time: Aim for 10–30 minutes of unprotected sun exposure several times a week, but avoid prolonged unprotected exposure during peak UV hours to prevent skin damage. Be cautious if the UV index is above 3 because this is when the risk of skin damage is higher and protection is recommended.
  
  The UV index is a measure of ultraviolet radiation from the sun that can affect your skin and eyes. A UV index of 0 to 2 is generally considered safe for outdoor activities with minimal precautions.
  
  Important: Spending more time in the sun without protection does not necessarily increase your vitamin D levels significantly beyond the body's natural limit. In fact, prolonged UVB exposure causes the vitamin D in your skin to degrade into an inactive form. This is a natural process that acts as a safeguard to prevent vitamin D toxicity.

Supplements

For individuals with limited sun exposure or higher needs, daily vitamin D supplements are recommended. A maintenance dose of 800–1,000 IU per day is typical, though higher doses may be required for deficiencies.

Pro tips:

• Always pair your vitamin D with magnesium. Why? Magnesium activates the vitamin D in your body, ensuring optimal absorption and making it work effectively. Without enough magnesium, you’re not getting the full benefit, no matter how much vitamin D you take.
• Take your vitamin D supplement after a meal containing healthy fats. Vitamin D is fat-soluble, so it is better absorbed when taken with or after food
• Remember to choose a supplement with vitamin D3 (cholecalciferol) over D2 (ergocalciferol). D3 is more effective than D2 at raising and maintaining your vitamin D levels.