Do You Get Vitamin D on a Cloudy Day?

July 25, 2025 Scott Chaverri

Short answer: Yes—but not as much.
Even when the skies are gray, your body can still make vitamin D from the sun. But how much you make depends on cloud thickness, time of day, season, and where you live. Let’s break it all down.

🌞 How Does Sunlight Help You Make Vitamin D?

Your body produces vitamin D when your skin is exposed to ultraviolet B (UVB) rays from sunlight. These rays trigger a chemical in your skin (called 7-dehydrocholesterol) to convert into vitamin D₃, which then gets processed by your liver and kidneys into the active form your body can use.

But there’s a catch:

Only UVB rays do the job (not UVA or visible light)
UVB is strongest when the sun is high in the sky—typically around midday

So, less sun = less UVB = less vitamin D.

🌥️ What Happens on a Cloudy Day?

Clouds block or scatter sunlight—including UVB rays. On a heavily overcast day, up to 90% of UVB can be filtered out. That means your body may produce far less vitamin D—even if you're outdoors.

But good news:
☀️ Some UVB still gets through, especially when cloud cover is thin or broken
📈 On partly cloudy days, UVB levels can spike in sun patches due to reflection around the cloud edges (called the “broken cloud effect”)
⏱️ You just may need more time in the sun to get the same vitamin D dose as you would on a clear day

✅ Yes, you can still make vitamin D on a cloudy day—but it’s less efficient.

🧠 Other Factors That Affect Vitamin D Production

Clouds aren’t the only thing that impact how much vitamin D your body makes. Here are a few others:

🕛 1. Time of Day

UVB rays are strongest midday (10 a.m. – 3 p.m.). Earlier or later? Much weaker rays, especially on cloudy days.

🌍 2. Location & Season

Closer to the equator = more consistent UVB year-round
Farther north or south (like in Canada or Scandinavia)? You might not get any vitamin D from the sun in winter—even if it’s sunny.

🧴 3. Sunscreen Use

Sunscreen blocks UVB—but real-life use doesn’t usually lead to deficiency. Most people don’t apply it perfectly, and incidental sun exposure still helps.

🧕 4. Clothing Coverage

The more skin you cover, the less vitamin D you’ll make. Long sleeves, hats, and winter layers = less surface area for UVB to hit.

🧬 5. Skin Tone

Darker skin has more melanin, which acts as a natural sunscreen. This means people with darker skin may need more sun exposure to make the same amount of vitamin D as lighter-skinned individuals.

⚖️ How to Get Enough Vitamin D—Even on Cloudy Days

Here are smart, safe strategies to maintain your vitamin D levels:

☁️ 1. Spend a Little More Time Outside

If it’s cloudy, add a few extra minutes. For example, if you usually need 10 minutes of sun on a clear day, you might need 20–30 minutes on an overcast day.

🕑 2. Go Outside Midday

Even if it’s cloudy, midday is still the best time for vitamin D because UVB rays are most direct.

🩳 3. Expose More Skin (When Appropriate)

Arms and legs out = more vitamin D. Of course, balance this with comfort and sun safety.

💊 4. Consider Supplements

In winter, or if you're at risk of deficiency, supplements are a safe, effective backup.

🔆 5. Use a UVB Light Therapy Lamp

Devices like the MitoSOLIS emit the specific UVB wavelength (300–315 nm) needed for vitamin D synthesis.

Great for high-latitude locations
Perfect for indoor use during dark winters
A few minutes a few times a week may help maintain healthy levels
Always follow usage instructions and safety guidelines

🧪 The Science Backs It Up

Multiple studies and expert organizations confirm:

Vitamin D is still produced on cloudy days, but less efficiently
UVB penetration varies based on cloud type, time, location, and personal factors
UVB lamps and supplements are recommended alternatives when sun exposure isn’t enough

Sources:

Engelsen O. (2010) Nutrients – UVB exposure and vitamin D status
Cancer Council Australia – Sunlight & vitamin D guidance
Royal Osteoporosis Society – Cloud cover and vitamin D tips
Healthline – Sunlight, sunscreen, and vitamin D
Overcoming MS – UV Index and Vitamin D Calculator

✅ Final Takeaway

Yes—you do get vitamin D on a cloudy day.
But you might need a little more time outside, or consider alternatives like supplements or UVB lamps if you’re in a low-sun area or during winter.

Keeping your vitamin D levels healthy supports:

Strong bones 🦴
A balanced immune system 🛡️
Healthy mood and energy 🌞

Cloudy skies don’t have to mean deficiency—just adapt your strategy.

⚠️ Disclaimer

The information provided in this article is for educational and informational purposes only and is not intended as medical advice or as a substitute for professional healthcare guidance.

MitoSOLIS does not make medical claims about the diagnosis, treatment, cure, or prevention of any disease or medical condition. The content on this website, including blog articles, is intended to help readers make informed decisions about general wellness and health topics, but should not be interpreted as specific medical guidance.

Always consult with a qualified healthcare provider before beginning any new health regimen, particularly if you have existing medical conditions, are pregnant or nursing, or are taking medications. The use of UVB light or any light therapy device should be done in accordance with manufacturer guidelines and under appropriate supervision if medically necessary.

Statements made on this website have not been evaluated by the U.S. Food and Drug Administration (FDA).