Can You Get Vitamin D From The Sun After 4PM? Best Times Explained

Many people wonder whether late afternoon sun exposure can help them meet their vitamin D needs. The short answer is: it depends on several factors, including your location, season, and skin type. While you can still produce some vitamin D after 4pm, the amount is typically much less than during midday hours.

Understanding when and how to get vitamin D from sunlight is crucial, as approximately 35% of American adults have insufficient vitamin D levels. This essential nutrient plays a vital role in bone health, immune function, and overall wellbeing.

This article explores the science behind vitamin D production, the optimal times for sun exposure, and whether afternoon sunlight after 4pm can effectively boost your vitamin D levels.

Understanding How Your Body Makes Vitamin D From Sunlight

Vitamin D production in your skin is a fascinating biological process that depends on specific types of ultraviolet radiation.

When ultraviolet B (UVB) rays from the sun hit your skin, they interact with a form of cholesterol called 7-dehydrocholesterol. This interaction triggers a chemical reaction that produces previtamin D3, which then converts to vitamin D3 (cholecalciferol) through a heat-dependent process.

The key factor here is UVB rays. Unlike UVA rays, which are present throughout the day and can penetrate clouds and glass, UVB rays are much more variable in their intensity and availability.

UVB ray intensity depends on:

• The angle of the sun in the sky
• Your geographic location and latitude
• The season and time of year
• Weather conditions and cloud cover
• Altitude and air pollution levels

This is why the time of day matters so much for vitamin D production.

Can You Get Vitamin D After 4PM?

The answer to this question is more nuanced than a simple yes or no.

After 4pm, vitamin D production becomes significantly less efficient in most locations. This is because the sun is lower in the sky, and its rays must travel through more of the Earth’s atmosphere to reach you. This longer path causes more UVB rays to be absorbed or scattered before they reach your skin.

The sun’s position creates what scientists call a higher “zenith angle.” When the sun is at a zenith angle greater than 50 degrees from directly overhead, very little vitamin D synthesis can occur, regardless of how long you stay in the sun.

However, there are exceptions:

During summer months: In locations closer to the equator or during peak summer, some UVB rays may still be available after 4pm, though at reduced levels. You might still produce small amounts of vitamin D, but you would need significantly longer exposure time compared to midday.

Geographic location matters: If you live in southern states like Florida, Texas, or California, you may have better chances of producing some vitamin D after 4pm compared to northern states like Minnesota or Maine.

In winter: After 4pm in winter months, vitamin D production is essentially impossible in most of the United States, as UVB rays are already minimal even during midday hours.

The Best Time to Get Vitamin D From Sun Exposure

Research consistently shows that midday sun exposure is the most efficient time for vitamin D production.

Between 10am and 2pm, particularly around noon when the sun is at its highest point, UVB rays are most intense. This means your skin can produce vitamin D more quickly, requiring less time in the sun to reach adequate levels.

For most people in the United States, this translates to:

Fair-skinned individuals: Approximately 10-15 minutes of midday sun exposure on exposed skin (arms, legs, back), 2-3 times per week during spring, summer, and fall months.

Medium-toned skin: Around 15-20 minutes of midday exposure, 2-3 times per week.

Dark-skinned individuals: Between 25-40 minutes of midday exposure, 2-3 times per week, as melanin reduces the skin’s ability to produce vitamin D from sunlight.

These recommendations assume you’re exposing significant areas of skin without sunscreen. The more skin you expose, the more efficiently your body can produce vitamin D.

Why Midday Sun Is More Effective Than Afternoon Sun

The science behind why midday beats afternoon for vitamin D production comes down to physics and atmospheric science.

When the sun is directly overhead at noon, its rays travel the shortest distance through the atmosphere. This means less UVB radiation is absorbed or scattered by:

• Ozone molecules in the stratosphere
• Oxygen and nitrogen in the atmosphere
• Water vapor and air pollution
• Dust and other particulate matter

As the afternoon progresses and the sun moves toward the horizon, its rays must travel through increasingly more atmosphere. By 4pm, depending on your location and season, the sun’s rays might travel through 2-3 times more atmosphere than at noon.

This increased atmospheric path absorbs a disproportionate amount of UVB rays compared to UVA rays. While you might still feel the sun’s warmth and see bright light after 4pm, the UVB component necessary for vitamin D synthesis has been largely filtered out.

Factors That Affect Vitamin D Production At Any Time

Beyond the time of day, several other factors influence whether and how much vitamin D your body can produce from sunlight.

Your Skin Tone and Melanin Content

Melanin acts as a natural sunscreen, protecting your skin from UV damage. However, this same protective mechanism also reduces vitamin D production.

People with darker skin tones need significantly more sun exposure to produce the same amount of vitamin D as lighter-skinned individuals. This is one reason why vitamin D deficiency rates are higher among African Americans and other darker-skinned populations living in northern latitudes.

Geographic Location and Latitude

Your distance from the equator dramatically affects vitamin D production year-round.

In northern parts of the United States (above 37 degrees north latitude, roughly a line from San Francisco to Richmond, Virginia), vitamin D synthesis is minimal or impossible during winter months, typically from November through February.

During these months, even midday sun exposure won’t produce adequate vitamin D, making afternoon sun exposure after 4pm completely ineffective for this purpose.

Season and Time of Year

Seasonal variation affects both the intensity of UVB rays and the hours during which they’re available.

In summer, the “vitamin D window” might extend from 9am to 3pm or even later in southern locations. In winter, this window shrinks dramatically and may only include a few hours around noon, if at all.

Cloud Cover and Weather

Clouds can reduce UVB radiation by up to 50% or more, depending on their thickness. Heavy cloud cover can essentially eliminate vitamin D production even during optimal midday hours.

Air Quality and Pollution

Air pollution and smog can absorb and scatter UVB rays, reducing the amount that reaches your skin. Urban areas with significant air pollution may experience reduced vitamin D production even during peak hours.

Altitude

Higher altitudes actually enhance vitamin D production because there’s less atmosphere to filter UVB rays. For every 1,000 feet of elevation gain, UVB exposure increases by approximately 4-5%.

How Much Skin Should You Expose?

The amount of skin you expose to sunlight directly correlates with how much vitamin D you can produce.

Experts generally recommend exposing approximately one-third of your skin surface area to optimize vitamin D production. This might include:

• Both arms and legs
• Arms, legs, and back
• Arms, legs, and abdomen

Exposing only your face and hands provides minimal vitamin D production because these represent a small percentage of your total skin surface area.

You can protect your face and eyes with a hat and sunglasses while exposing other body parts to the sun. This approach helps prevent sun damage to your facial skin while still allowing adequate vitamin D synthesis.

Does Sunscreen Block Vitamin D Production?

This is one of the most common questions about vitamin D and sun exposure.

Theoretically, sunscreen with an SPF of 30 or higher can reduce vitamin D production by more than 95% when applied properly. This is because sunscreen is designed to block or absorb UVB rays—the same rays needed for vitamin D synthesis.

However, real-world studies show more complex results. Research indicates that people who use sunscreen don’t necessarily have lower vitamin D levels than those who don’t. This may be because:

• Most people don’t apply enough sunscreen or reapply it frequently enough
• Sunscreen users may spend more total time in the sun, feeling protected from burns
• Some UVB rays still penetrate sunscreen, especially if not applied thickly or evenly

For optimal vitamin D production, consider getting 10-15 minutes of unprotected sun exposure during midday hours before applying sunscreen. After this brief period, apply broad-spectrum sunscreen to prevent skin damage if you’ll be spending more time outdoors.

Signs You’re Not Getting Enough Vitamin D

Many people with vitamin D deficiency don’t realize it because symptoms can be subtle or attributed to other causes.

Common signs of insufficient vitamin D include:

• Frequent infections or illness
• Fatigue and tiredness
• Bone and back pain
• Depression or mood changes
• Impaired wound healing
• Bone loss or osteoporosis
• Hair loss
• Muscle pain and weakness

If you experience several of these symptoms, especially if you have limited sun exposure or live in northern latitudes, consider having your vitamin D levels checked by your healthcare provider through a simple blood test.

Alternative Ways to Get Vitamin D

If afternoon sun is your only option, or if you live in a location with limited UVB exposure, you’ll need to consider other vitamin D sources.

Vitamin D-Rich Foods

Only a few foods naturally contain significant amounts of vitamin D:

• Fatty fish (salmon, mackerel, sardines, tuna)
• Cod liver oil
• Egg yolks (from chickens given vitamin D-supplemented feed)
• Beef liver
• Certain mushrooms exposed to UV light

Many foods are also fortified with vitamin D, including:

• Milk and dairy products
• Orange juice
• Breakfast cereals
• Plant-based milk alternatives

However, it’s challenging to get enough vitamin D from food alone. You would need to eat fatty fish almost daily to meet recommended intake levels.

Vitamin D Supplements

For many people, especially those living in northern climates or with limited sun exposure, vitamin D supplementation is the most practical solution.

The recommended daily intake is 600-800 IU (15-20 mcg) for most adults, though some experts suggest higher amounts, particularly during winter months or for individuals with deficiency risk factors.

If you’re considering supplements, consult with your healthcare provider first. They can test your current vitamin D levels and recommend an appropriate dosage based on your individual needs.

Balancing Vitamin D Production With Skin Cancer Risk

While vitamin D is essential for health, excessive sun exposure significantly increases your risk of skin cancer and premature skin aging.

The key is finding a balance: getting enough sun exposure for vitamin D production while protecting yourself from harmful effects of excessive UV radiation.

Here are strategies to achieve this balance:

• Limit unprotected sun exposure to 10-30 minutes during midday hours, depending on your skin tone
• Apply sunscreen after your brief vitamin D-producing exposure if you’ll be outside longer
• Never allow your skin to burn—burning significantly increases skin cancer risk
• Wear protective clothing, hats, and sunglasses for extended outdoor activities
• Seek shade during peak sun intensity hours if you’ll be outside for extended periods
• Be extra cautious if you have fair skin, a family history of skin cancer, or many moles
• Consider vitamin D supplementation as an alternative to extended sun exposure

Remember that skin damage from UV exposure is cumulative over your lifetime. Each sunburn and each period of excessive sun exposure adds to your skin cancer risk.

Special Considerations for Different Groups

Older Adults

As we age, our skin becomes less efficient at producing vitamin D. A 70-year-old produces about 25% less vitamin D from the same sun exposure compared to a 20-year-old.

Older adults also tend to spend less time outdoors and may have dietary restrictions that limit vitamin D intake. For these reasons, supplementation is often recommended for people over 65.

Infants and Young Children

Babies under 12 months should be kept out of direct sunlight as their skin is extremely sensitive to UV damage. The American Academy of Pediatrics recommends vitamin D supplementation for all infants.

Young children also need sun protection, making supplementation often the safer choice for meeting their vitamin D needs.

Pregnant and Breastfeeding Women

Vitamin D requirements increase during pregnancy and breastfeeding. Maternal vitamin D status affects both the mother’s and baby’s health.

Many prenatal vitamins contain vitamin D, but some women may need additional supplementation. Discuss your needs with your healthcare provider.

People With Certain Health Conditions

Some medical conditions affect vitamin D absorption or metabolism, including:

• Crohn’s disease and celiac disease
• Obesity (vitamin D gets sequestered in fat tissue)
• Kidney and liver diseases
• Cystic fibrosis

If you have any of these conditions, work with your healthcare provider to monitor your vitamin D levels and determine appropriate supplementation.

Practical Tips for Optimizing Your Vitamin D Levels

Here are actionable strategies to ensure you maintain healthy vitamin D levels:

During spring, summer, and early fall:

• Aim for 10-30 minutes of midday sun exposure on bare arms and legs, 2-3 times per week
• Try to schedule outdoor activities between 10am and 2pm when possible
• If you can see your shadow and it’s shorter than your height, UVB rays are likely present
• Don’t rely on sun exposure after 4pm for vitamin D production

During late fall, winter, and early spring:

• Consider taking a vitamin D supplement, especially if you live above 37 degrees north latitude
• Increase consumption of vitamin D-rich and fortified foods
• If possible, plan a winter vacation to sunnier, lower-latitude locations
• Have your vitamin D levels checked, particularly if you have risk factors for deficiency

Year-round strategies:

• Maintain a varied diet that includes vitamin D sources
• Exercise outdoors when weather permits
• Keep windows open when possible (though UVB can’t penetrate glass, outdoor activity is still beneficial)
• Monitor your health for signs of deficiency
• Have your vitamin D levels tested annually, especially if you have limited sun exposure

The Bottom Line

While it’s technically possible to produce small amounts of vitamin D from sun exposure after 4pm during summer months in some locations, it’s far from optimal. The intensity of UVB rays decreases significantly as the afternoon progresses, making vitamin D production increasingly inefficient.

For most effective vitamin D synthesis, aim for midday sun exposure between 10am and 2pm, when the sun is highest in the sky. Just 10-30 minutes of midday exposure on bare skin, several times per week, is typically sufficient for most people during appropriate seasons.

However, remember that multiple factors influence vitamin D production, including your skin tone, geographic location, season, and weather conditions. People with darker skin, those living in northern latitudes, and individuals with limited sun exposure may need longer exposure times or should consider supplementation.

The key is balancing adequate vitamin D production with protection from excessive sun exposure and skin cancer risk. For many people, a combination of sensible sun exposure, vitamin D-rich foods, and supplementation provides the best approach to maintaining optimal vitamin D levels year-round.

If you’re concerned about your vitamin D status, consult with your healthcare provider. They can test your levels and provide personalized recommendations based on your individual circumstances, health status, and risk factors.

Sources:

• National Institutes of Health – Vitamin D Deficiency Statistics
• PMC – Optimal Time for Vitamin D Synthesis
• MDPI Nutrients – Sun Exposure Guidelines
• FDA – Vitamin D Daily Values
• PMC – Seasonal Variations in Vitamin D Production
• PubMed – Geographic Latitude and Vitamin D
• Journal of Investigative Dermatology – Skin Exposure Recommendations
• PubMed – Sunscreen and Vitamin D Production
• PMC – Sunscreen Effects on Vitamin D Levels