Nutrition Diet: Can We Get Vitamin D Through a Glass Window?

November 10, 2025 •

4 min read

Did you know that over one in three Australian adults may have a vitamin D deficiency? This raises a very common question: Can we get vitamin D through a glass window? The definitive answer is no, a fact that reveals a critical misunderstanding about how our bodies produce this vital nutrient.

Quick Summary

Standard window glass effectively blocks the specific ultraviolet B (UVB) rays required for the body to synthesize vitamin D. While sun exposure through a window provides warmth and light, it does not contribute to vitamin D production. To maintain adequate levels, one must rely on direct sun exposure, dietary sources, or supplementation.

Key Points

Glass blocks UVB rays: Standard window glass prevents the ultraviolet B (UVB) rays required for vitamin D production from reaching your skin.
UVA vs. UVB: Glass lets through UVA rays, which contribute to skin aging and cancer risk, but not the UVB rays needed for vitamin D synthesis.
In-car exposure is ineffective: You will not produce vitamin D while driving or sitting in a car with the windows up, as the glass blocks UVB radiation.
Supplements are a reliable alternative: For those with limited sun exposure, dietary supplements, particularly vitamin D3, are an effective way to maintain adequate levels.
Dietary sources include fatty fish: Foods like salmon, tuna, mackerel, and fortified dairy or plant-based milks and cereals can help you meet your vitamin D needs.
Sun exposure must be direct: To produce vitamin D, skin needs to be exposed to direct, unfiltered sunlight, generally for 5-30 minutes, depending on various factors.
Deficiency symptoms are subtle: Many people with a deficiency experience fatigue, muscle weakness, or bone pain, so awareness is key.

The Science Behind Vitamin D Synthesis

Your body's primary method for producing vitamin D is through exposure to sunlight. When your bare skin is exposed to the sun's ultraviolet B (UVB) rays, it triggers a reaction that converts a form of cholesterol in your skin cells into previtamin D3. This previtamin D3 is then further converted into the usable form of vitamin D. However, not all sunlight is created equal when it comes to this process. The process is dependent specifically on UVB radiation, which is a particular wavelength of sunlight.

The Glass Barrier: Why Windows Fail

The reason you cannot absorb vitamin D through a closed window comes down to the properties of glass. Standard glass, including what is found in homes and cars, acts as an effective filter. While it allows ultraviolet A (UVA) rays to pass through, it blocks virtually all UVB rays. This means that while you might feel warmth and even get a tan or experience skin aging from the UVA rays, your body's vitamin D synthesis process is not being activated. Laminated glass, often used in car windshields, is even more effective at blocking UV radiation.

Why the Distinction Matters

Understanding the difference between UVA and UVB is key to grasping why windows are an ineffective source of vitamin D. UVA rays, which pass through glass, penetrate deeper into the skin and contribute to aging and a higher risk of skin cancer. In contrast, the UVB rays, which are blocked by glass, primarily affect the skin's surface and are responsible for both sunburn and vitamin D production. This is why you can still experience sun-related skin damage (caused by UVA) while indoors, but receive no vitamin D benefits. This nuance highlights the importance of safe, direct sun exposure outdoors for a short duration, or seeking alternative sources for adequate intake. For those who spend significant time indoors, especially during winter months, relying on sunlight through a window is a flawed strategy for maintaining healthy vitamin D levels.

Comparison: Direct Sun vs. Through a Window


Feature	Direct Sun Exposure (Outdoors)	Through a Glass Window (Indoors)
Exposure to UVB Rays	Yes	No, glass blocks them
Exposure to UVA Rays	Yes	Yes, most pass through glass
Vitamin D Synthesis	Yes, body produces vitamin D3	No, no production occurs
Risk of Sunburn	Yes, if prolonged and unprotected	Very unlikely, as glass blocks most UVB
Risk of Skin Aging	Yes	Yes, due to UVA exposure

Alternative and Reliable Ways to Get Vitamin D

Since relying on sunlight through glass is not an option, you must explore other methods to ensure you get enough of this crucial nutrient. These alternatives are particularly important for those with limited outdoor access, specific skin tones that require longer sun exposure, or during winter when UVB is less intense.

Dietary Sources: Few foods naturally contain high levels of vitamin D. However, some excellent sources include fatty fish like salmon, tuna, mackerel, and trout. Beef liver, cheese, and egg yolks also contain smaller amounts.
Fortified Foods: To combat widespread deficiency, many food products are fortified with vitamin D. Check the nutrition labels on products like milk (dairy and plant-based), certain breakfast cereals, and orange juice.
Supplements: Vitamin D supplements are a highly reliable way to maintain adequate levels, especially for those in northern latitudes or with other risk factors. Vitamin D3 supplements are generally considered more effective at raising blood levels than D2. It's best to consult a healthcare provider to determine the right dosage for you.
UV-Exposed Mushrooms: Some mushrooms, when grown under ultraviolet light, have a higher vitamin D content.

Symptoms of Vitamin D Deficiency

A lack of sufficient vitamin D can lead to various health complications. In children, it can cause rickets, while in adults, it can result in osteomalacia, a softening of the bones. Being aware of the symptoms can prompt you to get tested and address a potential deficiency.

Fatigue and a general sense of tiredness
Bone and muscle pain, particularly in the back and joints
Muscle weakness, aches, or cramps
Depressed mood or seasonal affective disorder
Impaired wound healing
Frequent infections or a weakened immune system
Bone loss or increased risk of fractures

Conclusion

While a sunny window seat might feel pleasant, it is completely ineffective for getting your daily dose of vitamin D. The glass barrier prevents the necessary UVB rays from reaching your skin, effectively halting the vitamin D synthesis process. This fundamental fact underscores the need for a balanced approach to maintaining healthy vitamin D levels. For most people, a combination of sensible, direct sun exposure, a diet rich in vitamin D sources, and—when necessary—high-quality supplements is the best strategy. Prioritizing safe and effective methods over the myth of window-filtered sun is essential for your overall health and well-being. For more detailed information on vitamin D, consult reputable health resources like the NIH Office of Dietary Supplements.

Frequently Asked Questions

You cannot get vitamin D from the sun through a window because standard glass blocks the ultraviolet B (UVB) rays needed for your skin to produce vitamin D. Only the UVA rays, which don't stimulate vitamin D production, can pass through.

While it's unlikely you will get a traditional sunburn through a standard glass window, you can still experience skin damage. This is because glass allows UVA rays to pass through, which penetrate deeply into the skin and contribute to premature aging and an increased risk of skin cancer.

If you cannot get enough direct sunlight, you can obtain vitamin D through diet and supplements. Good dietary sources include fatty fish like salmon and fortified foods such as milk and cereals. Taking a vitamin D3 supplement is also a very effective method.

Yes, some foods are naturally high in vitamin D, though they are limited. Fatty fish like salmon, tuna, and mackerel are excellent sources. Other foods with smaller amounts include beef liver, egg yolks, and certain mushrooms grown under UV light.

Symptoms of vitamin D deficiency can be subtle and include fatigue, bone pain, muscle weakness, and a depressed mood. In severe cases, it can lead to conditions like rickets in children and osteomalacia in adults.

The use of tanning beds for vitamin D is not recommended by health experts. While some tanning beds emit UVB rays, they also expose you to high levels of UV radiation, significantly increasing your risk of skin cancer.

The amount of sun exposure needed varies based on factors like time of day, season, location, and skin tone. Generally, 5 to 30 minutes of midday sun exposure to the face, arms, and legs, a couple of times per week, can be sufficient. However, it's crucial to balance this with safe sun practices to prevent skin damage.

Vitamin D2 (ergocalciferol) is derived from plant sources, while vitamin D3 (cholecalciferol) typically comes from animal sources or lichen. Most evidence suggests that D3 is more effective at raising and maintaining blood vitamin D levels than D2.