Can You Get Vitamin D From the Sun If It Is Cloudy?

December 19, 2025 •

4 min read

According to the US National Weather Service and Environmental Protection Agency, up to 89% of UV rays can penetrate thin cloud cover. This surprising fact reveals that even when the sky is overcast, it is still possible to get vitamin D from the sun. However, the amount produced and the time required are both affected by the density of the clouds and other key factors.

Quick Summary

Despite widespread belief, you can still synthesize vitamin D from sunlight on overcast days. The quantity produced depends on cloud density, time of day, and other individual factors. It may take longer than on a clear day to absorb a sufficient amount of UVB radiation for your body to produce the nutrient.

Key Points

Yes, you can get vitamin D: Even with thin to moderate cloud cover, enough UVB radiation can pass through to stimulate vitamin D synthesis in the skin.
Thick clouds reduce absorption: Heavy or overcast conditions significantly decrease the amount of available UVB, making vitamin D production far less efficient.
Midday is still the best time: The sun's rays are strongest and most direct between 10 a.m. and 3 p.m., making this the optimal window for sun exposure, even when it's cloudy.
Personal factors matter: Skin tone, age, latitude, and clothing all influence how much vitamin D your body produces from sunlight.
Combine with other sources: On persistently cloudy days or in northern latitudes during winter, dietary sources and supplements are reliable alternatives to maintain sufficient vitamin D.
Protect your skin: The risk of sunburn and long-term skin damage from UV rays still exists on cloudy days, so exercising caution is important.

Yes, But It's Complicated: How Clouds Affect Vitamin D Production

For years, many people have assumed that a bright, sunny day is required for vitamin D synthesis from the sun. The reality is more nuanced; while clouds do block some ultraviolet B (UVB) radiation—the specific light frequency that triggers vitamin D production in the skin—they don't block all of it. The amount of UVB that reaches the Earth's surface and, by extension, your skin, is dependent on several variables. Understanding these factors can help you optimize your outdoor exposure, even on overcast days.

The Science Behind the Clouds

Clouds are essentially collections of water droplets or ice crystals suspended in the atmosphere. Their thickness and composition determine how much UVB radiation they filter out.

Thin clouds: These allow a significant portion of UVB rays to pass through. Light, broken, or scattered clouds can permit 70-90% of UVB to reach the ground.
Thick, heavy clouds: Overcast conditions can reduce UVB penetration dramatically, sometimes blocking as much as 90% of the radiation.
Time of day: As with a clear day, the sun's rays are most direct and powerful during the midday hours (approximately 10 a.m. to 3 p.m.). This is the optimal time for vitamin D production, even with some cloud cover. Outside of this window, the sun’s rays travel through more of the atmosphere, reducing the amount of UVB that reaches your skin, regardless of the clouds.

Factors Influencing Your Personal Vitamin D Synthesis

Beyond the clouds, several individual factors can affect how much vitamin D your body produces. This is why a one-size-fits-all recommendation for sun exposure isn't feasible.

Skin Pigmentation: Melanin, the pigment that determines skin color, acts as a natural sunscreen. People with darker skin have more melanin and therefore require more sun exposure to produce the same amount of vitamin D as someone with lighter skin.
Latitude and Season: The angle of the sun's rays is steeper farther from the equator. In higher latitudes, particularly during the winter, the sun's angle is low, and the UVB rays are too weak to stimulate significant vitamin D synthesis. This effect is compounded on a cloudy day.
Age: As people age, their skin becomes less efficient at producing vitamin D from sunlight.
Sunscreen and Clothing: SPF 15 sunscreen can block the UVB rays needed for vitamin D production. Clothing also physically blocks the rays from reaching your skin.

Optimizing Vitamin D Absorption on Cloudy Days

While sun exposure is a primary source of vitamin D, it's not the only one. Combining smart sun practices with other strategies can help ensure you meet your daily requirements, especially when the weather is uncooperative.

Comparison: Clear vs. Cloudy Day Sun Exposure


Aspect	Clear Day	Cloudy Day
UVB Penetration	High and direct	Variable; depends on cloud thickness
Efficiency	Very high, requires less time	Lower, may require longer exposure
Sunburn Risk	Significant, even with short exposure	Still possible, especially with thin clouds
Recommended Exposure Time	10-30 minutes for many individuals	May need slightly longer, up to an hour or more
Best Time for Exposure	Midday (10 a.m. - 3 p.m.)	Midday (10 a.m. - 3 p.m.)
Recommended Action	Use sun protection after initial exposure	Stay aware of conditions; combine with other sources

Other Sources of Vitamin D

Dietary Sources: Incorporate fatty fish (salmon, tuna), fortified foods (milk, cereal), and egg yolks into your diet.
Supplements: Vitamin D supplements are a reliable way to ensure consistent intake, especially for those living in northern latitudes or with darker skin. Consult a healthcare professional to determine the right dosage.
Tanning Beds: Some commercial tanning beds use bulbs that emit UVB radiation. However, limiting UV exposure is recommended to reduce the risk of skin cancer.

The Importance of Balanced Approach

It is crucial to balance the benefits of sun exposure with the risks of UV radiation, which is a known carcinogen. Always be mindful of the UV index, even on a cloudy day, as you can still get burned. The World Health Organization provides guidance on safe sun exposure. Combining a variety of strategies is the most effective and safest approach for maintaining adequate vitamin D levels.

Conclusion

In summary, the answer to the question, "Can you get vitamin D from the sun if it is cloudy?" is a definitive yes, though with several important caveats. While cloud cover can significantly reduce the amount of UVB radiation reaching the Earth's surface, it does not block it completely. The density of the clouds, the time of day, and your personal characteristics like skin tone and age all play a role in how much vitamin D your body can produce. On lightly overcast days, a moderate amount of midday exposure can still be effective. However, on heavily clouded days or during winter in higher latitudes, relying on sunlight alone is often insufficient. A balanced strategy that includes safe sun exposure, dietary sources, and supplements is the most reliable way to ensure you maintain optimal vitamin D levels for your health.

World Health Organization information on UV protection provides valuable insights into managing sun exposure safely.

Frequently Asked Questions

The amount varies greatly depending on the thickness of the cloud cover. Thin clouds may allow up to 89% of UVB rays to pass, while thick, heavy clouds can block over 70%.

Yes, absolutely. The UV rays that cause sunburn can still penetrate cloud cover. In fact, on some days with broken or thin clouds, reflected rays can be more intense, so it is important to still take precautions.

Yes. In winter, especially in higher latitudes, the sun is lower in the sky, meaning UVB rays are already less potent. Cloud cover during this time further diminishes the synthesis of vitamin D, making it much harder to produce.

Just like on a clear day, the best time for vitamin D synthesis is midday, roughly between 10 a.m. and 3 p.m., when the sun’s rays are most direct.

In most cases, yes. Because clouds filter out some of the UVB radiation, you may need to spend more time outdoors to achieve the same level of vitamin D synthesis as on a clear day.

Good dietary sources of vitamin D include fatty fish like salmon and tuna, fortified milk and cereals, and egg yolks.

While older adults can still produce vitamin D from the sun, their skin's efficiency at doing so decreases with age. The combination of age and cloud cover makes it particularly difficult to rely on sun exposure alone, making supplements a vital consideration.