How long do you need to be outside in winter to get enough vitamin D?

October 31, 2025 •

4 min read

According to the National Institutes of Health, vitamin D levels can drop significantly from late fall to early spring, especially for those living in higher latitudes, due to reduced sunlight. Knowing how long you need to be outside in winter to get enough vitamin D is essential for maintaining your health throughout the colder months.

Quick Summary

The duration of outdoor time required to synthesize adequate vitamin D in winter varies by location, skin tone, and time of day. In northern latitudes, synthesis is significantly limited, necessitating longer exposure. Midday is the optimal time for sun exposure, but many rely on dietary sources or supplements for sufficient vitamin D.

Key Points

Limited Winter Sunlight: In regions with higher latitudes (like the northern U.S. or UK), the sun's angle is too low between October and March for effective vitamin D synthesis.
Midday Exposure Is Best: To maximize potential vitamin D production from winter sun, spend time outdoors between 10 a.m. and 3 p.m., exposing your face and forearms.
Duration Varies: The amount of time needed ranges from 10–30 minutes for lighter skin to significantly longer (3–6 times) for darker skin tones.
Supplements are Recommended: For most people in northern latitudes, health experts recommend taking a daily vitamin D supplement during winter, as sunlight exposure is often inadequate.
Dietary Sources are Key: Incorporate foods like fatty fish, fortified milk and cereals, and eggs into your diet to boost vitamin D intake, especially when sun exposure is limited.
Check with a Professional: A blood test can confirm if you have a deficiency, and a doctor can help determine the right dose for a supplement.
UV Lamps are an Option: Specialized UV lamps can help some individuals produce vitamin D when natural sunlight is scarce, but they require careful use.

Why Winter Reduces Vitamin D Synthesis

During the winter, several factors combine to significantly reduce the body's ability to produce vitamin D from sunlight. The sun's angle is lower, especially in regions farther from the equator, which means the UVB rays needed for vitamin D synthesis are weaker and filtered out more effectively by the atmosphere. Shorter daylight hours and increased cloud cover also play a major role in limiting overall sun exposure. Additionally, winter clothing covers most of the skin, leaving very little surface area exposed to the sun's rays. For most people, this combination of factors means that relying solely on sun exposure during the colder months is not enough to maintain adequate vitamin D levels.

The Role of UV Index and Latitude

The UV (Ultraviolet) Index is a crucial indicator of the sun's strength. In winter, for many northern regions (above roughly 37 degrees latitude), the UV index often drops below 3. When the UV index is this low, the UVB radiation is generally insufficient for the body to produce vitamin D. This phenomenon is sometimes referred to as the “vitamin D winter”. For example, studies show that at latitudes similar to Boston, Massachusetts, sun exposure in winter is much less effective than in a sunny location like Miami, Florida, requiring far more time to produce the same amount of vitamin D. This geographic and seasonal variation is why a one-size-fits-all approach to sun exposure isn't effective for everyone.

How Much Time Do You Really Need?

The exact amount of time needed to be outside in winter to get enough vitamin D is not precise and varies based on numerous factors. However, general guidelines exist. Experts often recommend aiming for 10 to 30 minutes of sun exposure around midday, with face and arms uncovered, on most days of the week. It is important to note that individuals with darker skin tones, due to higher melanin content, require significantly longer exposure times—sometimes 3 to 6 times more—to produce the same amount of vitamin D as those with lighter skin. These are only general recommendations, and for many people, especially in high latitudes, even this increased exposure won't be enough.

Beyond Sunlight: Other Methods for Maintaining Vitamin D

Given the challenges of relying on winter sunlight, it's prudent to consider alternative sources. Fortunately, several effective options are available to help maintain healthy vitamin D levels throughout the year.

Dietary Intake

Fatty Fish: Excellent sources include salmon, mackerel, tuna, and sardines.
Fortified Foods: Many common foods are fortified with vitamin D, such as milk, breakfast cereals, yogurt, and orange juice.
Other Sources: Egg yolks, red meat, liver, and UV-exposed mushrooms also contain vitamin D.

Supplementation

Many healthcare professionals recommend a daily vitamin D supplement during the autumn and winter, especially for those in northern climates.
Vitamin D3 is often recommended over D2 as it is more effective at raising blood levels.
It is crucial to consult with a healthcare provider to determine the correct dosage, as excessive intake can be harmful.

UV Lamps

Specialized UV lamps can be used to simulate sunlight and stimulate vitamin D production.
This option can be particularly useful for those in northern latitudes or with very limited outdoor time.

Comparison of Winter Vitamin D Sources


Source	Effectiveness in Winter	Best For	Considerations
Sunlight Exposure	Low to moderate, depending on latitude and skin type. Ineffective in many northern regions.	Supplementing other sources, boosting mood.	Requires specific times, minimal skin coverage, and varies widely by individual and location.
Dietary Sources	Consistent year-round.	All individuals, especially those who prefer natural intake.	May be difficult to get enough from food alone, especially if dietary restrictions apply.
Oral Supplements	Highly effective and reliable.	Individuals in high-latitude regions, those with darker skin, and anyone with proven deficiency.	Correct dosage is crucial; a doctor's advice is recommended.
UV Lamps	Effective but less common.	Individuals with limited outdoor time or severe deficiency who can't take supplements.	Risks associated with UV exposure; require specific equipment.

Conclusion: A Multi-pronged Approach is Best

In summary, the amount of time needed outside in winter to get enough vitamin D is highly variable and often insufficient for many people. While spending time outdoors during midday can help, particularly for those with lighter skin in more southern latitudes, it should not be relied upon as the sole source. For most, particularly during the months of October through March, a combination of dietary sources and supplements is the most reliable way to maintain adequate vitamin D levels and support overall health. Before beginning any supplementation regimen, it is always recommended to consult with a healthcare professional to determine the best approach for your individual needs. For more details on recommended dietary allowances for vitamin D, visit the NIH Office of Dietary Supplements website.

Additional Actions for Healthy Vitamin D Levels

To maximize your vitamin D status during the winter months, integrate these habits into your routine:

Prioritize Midday Exposure: If you can get outside, do so during the peak hours of 10 a.m. to 3 p.m., when UVB rays are strongest.
Combine with Physical Activity: A brisk midday walk not only provides sun exposure but also offers the additional health benefits of exercise.
Choose Fortified Foods: Actively seek out fortified products like milk and cereals when grocery shopping to increase dietary intake.
Cook with Oily Fish: Incorporate dishes with fatty fish like salmon or mackerel into your meal plan at least a couple of times a week.
Consult a Doctor: If you suspect a deficiency or are unsure about supplementation, get a blood test to check your levels and discuss options with a healthcare provider.
Be Mindful of Skin Tone: Remember that darker skin requires longer exposure times to produce the same amount of vitamin D.
Don't Rely on Windows: UVB rays do not penetrate glass, so sitting by a sunny window won't help your body produce vitamin D.

Frequently Asked Questions

For most people living at latitudes above approximately 37 degrees north (e.g., Boston, MA), the angle of the sun in winter is too low for the body to synthesize adequate vitamin D from sun exposure alone.

The best time for sun exposure to produce vitamin D in winter is around midday, typically between 10 a.m. and 3 p.m., when the sun's UVB rays are strongest.

Yes, skin tone significantly impacts vitamin D production. Individuals with darker skin tones have more melanin, which acts as a natural sunscreen, and therefore require longer sun exposure than those with lighter skin to produce the same amount of vitamin D.

No, UVB rays do not penetrate glass. Therefore, sitting by a sunny window in your home or car will not help your body produce vitamin D from sunlight.

Good dietary sources of vitamin D include fatty fish (salmon, mackerel), fortified foods like milk and cereals, egg yolks, and certain types of mushrooms that have been exposed to UV light.

In winter, especially in northern regions, it is difficult to get enough vitamin D from sunlight alone. Supplements are often a more reliable and consistent way to ensure adequate intake during the colder months.

Depending on the latitude, a person with darker skin may need significantly longer sun exposure than a person with lighter skin. For example, some studies suggest up to 3 to 6 times longer, meaning that relying on sunlight alone is often not a viable option.