Can you get vitamin D from sunshine through the window?

January 9, 2026 •

4 min read

According to the National Institutes of Health, your skin does not produce vitamin D when sunlight is filtered through a window, as the glass blocks the necessary UV rays. This surprising fact debunks the common myth that you can get vitamin D from sunshine through the window, impacting how many people address their vitamin levels and sun protection.

Quick Summary

Standard window glass effectively blocks the ultraviolet B (UVB) rays necessary for your body to synthesize vitamin D. Indoor sun exposure is therefore an ineffective way to get the 'sunshine vitamin,' and alternatives like fortified foods and supplements are required.

Key Points

UVB Rays Blocked: Standard window glass effectively blocks the UVB rays from sunlight that are necessary for your body to produce vitamin D.
UVA Rays Penetrate: While UVB is blocked, most UVA radiation passes through glass, which can still cause skin aging and damage over time.
Indoor Sun is Ineffective: Relying on indoor sunlight for vitamin D synthesis is a myth and an unreliable method for maintaining healthy levels.
Supplementation is a Safe Alternative: For those with limited sun exposure, vitamin D supplements are a reliable way to ensure adequate intake.
Dietary Sources Help: Eating fatty fish, fortified foods, and mushrooms exposed to UV light can contribute to your daily vitamin D needs.
Safe Outdoor Exposure is Key: Brief, unprotected periods of direct sun exposure can produce vitamin D, but proper sun protection (like sunscreen) is needed to mitigate the risk of skin cancer during longer exposure times.

The Science Behind Window Glass and UV Rays

To understand why you can't get vitamin D from sunshine through a window, you need to know a little about ultraviolet (UV) radiation. Sunlight reaches Earth's surface in two primary forms: UVA and UVB rays. It is the UVB radiation that triggers your skin to produce vitamin D. Standard window glass, however, acts as an efficient barrier to these essential rays.

Understanding UVA and UVB

UVA (Ultraviolet A) Rays: These have a longer wavelength and can penetrate deep into the skin, contributing to premature aging, wrinkles, and other long-term skin damage. Critically, most window glass allows UVA rays to pass through relatively unimpeded.
UVB (Ultraviolet B) Rays: These have a shorter wavelength and are primarily responsible for causing sunburn. They are also the specific wavelength that interacts with a cholesterol-like molecule in your skin to begin the process of vitamin D synthesis.

How Glass Selectively Filters UV

While glass appears transparent to visible light, its atomic structure makes it opaque to UVB rays. The molecular composition of the glass absorbs nearly all UVB radiation, preventing it from reaching your skin. This is why you can sit in a sunny spot indoors and feel warmth and see bright light, but you will not get sunburned (unless exposed for a very long period) and your body will not produce vitamin D. This is a crucial distinction that many people miss, often mistaking the visible light and warmth for the health-giving properties of direct sunlight.

Why Indoor Sunbathing Won't Help Your Vitamin D Levels

For those who spend significant time indoors, such as working from home or living in northern latitudes during winter, the implications are clear: relying on sunlight through a window is a flawed strategy for maintaining healthy vitamin D levels. Studies confirm that people who spend most of their time next to sunny windows are still susceptible to vitamin D deficiency. The misconception that any exposure to sunshine is beneficial for vitamin D production can lead to a false sense of security and a lack of proper supplementation when needed.

Furthermore, the UVA rays that do pass through glass still pose a health risk. While they won't help with vitamin D, prolonged indoor sun exposure can still cause skin aging and increase the risk of skin cancer. This means that sitting by a window for long periods offers the potential for skin damage without any of the vitamin D benefits, highlighting the importance of understanding the limitations of window-filtered light.

Comparison: UVA vs. UVB Through Glass


Feature	UVA Rays	UVB Rays
Wavelength	Long	Short
Passes Through Window Glass?	Yes, mostly	No, mostly blocked
Effect on Skin	Skin aging, deep damage	Sunburn (Blocked by glass)
Vitamin D Production?	No	Yes (Blocked by glass)
Cancer Risk	Increased risk over time	Primary cause of sunburn and skin cancer (when unfiltered)

Safe and Effective Ways to Get Vitamin D

Since indoor sun exposure is not a viable option for vitamin D synthesis, it's important to turn to more reliable sources. A combination of safe sun exposure, diet, and supplements is often the most effective approach for most people.

Reliable Sources of Vitamin D:

Diet: Few foods naturally contain significant vitamin D, but some are excellent sources. These include fatty fish like salmon, tuna, and mackerel; cod liver oil; and beef liver.
Fortified Foods: Many foods, including milk, cereals, and orange juice, are fortified with vitamin D. Checking nutrition labels is a good way to identify these products.
Supplements: Vitamin D supplements are a highly reliable way to ensure adequate intake, especially for those with limited outdoor sun exposure or medical conditions affecting absorption. Supplements come in two forms: D2 (ergocalciferol) and D3 (cholecalciferol), with D3 often being cited as more effective.
Direct Outdoor Sun Exposure: Spending a brief period outdoors without sunscreen can stimulate vitamin D production. The recommended duration and frequency depend on factors like skin tone, time of day, season, and geographic location. Experts suggest that for fair-skinned people, 10-15 minutes of direct sun exposure during peak hours is often enough. However, this must be balanced carefully against the risks of skin cancer, and sunscreen should always be used for prolonged periods.

For more detailed guidance on safe sun exposure and vitamin D intake, you can consult resources like the Harvard Health website, which provides comprehensive information on balancing sun benefits with sun safety. [https://www.health.harvard.edu/staying-healthy/6-things-you-should-know-about-vitamin-d]

Conclusion: The Final Word on Window Sunshine and Vitamin D

In summary, the comforting sensation of sun streaming through a window is not sufficient for your body to produce vitamin D. The standard glass used in homes and cars effectively filters out the crucial UVB rays needed for this process, while allowing potentially harmful UVA rays to pass through. Relying on indoor sunlight for your vitamin D needs is therefore an ineffective and potentially risky practice. To maintain healthy vitamin D levels, a combination of dietary sources, fortified foods, and supplements is the most dependable and safest strategy, with careful, brief direct sun exposure as an occasional option for those who can tolerate it. For personalized advice, it is always recommended to consult with a healthcare provider to determine the best approach for your individual health needs.

Frequently Asked Questions

Yes, UV-blocking window films are specifically designed to block the vast majority of UV rays, including the UVB radiation needed for vitamin D synthesis.

No, a car's windows, particularly the windshield, are designed to block most UVB rays, so you will not produce vitamin D while inside.

The best ways to get vitamin D without sunlight are through dietary supplements (often the most reliable method), consuming fatty fish and cod liver oil, and eating fortified foods like milk, cereal, and orange juice.

Vitamin D is crucial for absorbing calcium to maintain healthy bones, teeth, and muscles. It also plays a vital role in immune function, brain health, and mood regulation.

For fair-skinned individuals, a few minutes of direct midday sun exposure on bare skin, a couple of times a week, can be sufficient. However, this varies widely based on latitude, season, skin tone, and time of day.

You cannot get too much vitamin D from sun exposure because your body has a mechanism that regulates and limits its production. However, excessive sun exposure is harmful and increases the risk of skin damage and cancer.

Some specialized sun lamps, often used for treating Seasonal Affective Disorder (SAD) or certain skin conditions, may emit UVB light. However, you should consult a doctor before using them, as they must be used carefully and correctly.

While sunscreen blocks UVB rays, studies show that most people don't apply enough to completely block all vitamin D production. You can still maintain adequate vitamin D levels while using sunscreen.