How to Expose to Sun for Vitamin D Safely and Effectively

December 30, 2025 •

5 min read

According to the NIH, nearly one in four people in the United States have vitamin D blood levels that are too low for optimal health. Knowing how to expose to sun for vitamin D safely is crucial, as sunlight is a primary natural source, yet overexposure carries significant risks like skin cancer.

Quick Summary

This guide provides a balanced approach to obtaining vitamin D from the sun, detailing the best time of day, recommended duration based on skin type and location, and emphasizing safe practices to minimize skin cancer risk. It also explores alternative sources like fortified foods and supplements.

Key Points

Optimal Timing: The best time to synthesize vitamin D from the sun is typically between 10 a.m. and 3 p.m., but this is also when UV rays are strongest and sunburn risk is highest.
Duration Varies: 5-30 minutes of unprotected sun exposure is a common recommendation, with the duration needed increasing for people with darker skin, at higher latitudes, or on cloudy days.
Skin Color Matters: Melanin reduces the amount of UV radiation that penetrates the skin, meaning individuals with darker skin tones require significantly longer sun exposure to produce sufficient vitamin D.
Sunscreen's Role: While sunscreen can block UVB rays, typical application does not completely eliminate vitamin D production. Health experts recommend applying it after a brief, safe exposure period to prevent skin cancer.
Supplements are Key: Relying solely on the sun is often insufficient, especially in winter or for high-risk individuals. Dietary supplements and fortified foods are crucial for maintaining adequate vitamin D levels year-round.
Sun Safety First: Prioritizing sun safety by limiting unprotected exposure and using sunscreen is essential to mitigate the risk of skin cancer, the most preventable form of the disease.

The Science Behind Sunlight and Vitamin D Production

Your body produces vitamin D when exposed to ultraviolet B (UVB) rays from the sun. A compound in your skin, 7-dehydrocholesterol, absorbs UVB radiation and converts it into previtamin D3, which is then isomerized into vitamin D3. The liver and kidneys then process this into the active form of vitamin D that your body can use. The amount of UVB available and your skin's ability to absorb it are the two most important factors influencing this process.

Factors Influencing Your Vitamin D Synthesis

Several variables determine how effectively your body can produce vitamin D from sunlight, meaning there is no one-size-fits-all answer.

Season and Latitude: In many regions, the sun's angle is too low during autumn and winter for enough UVB radiation to reach your skin. The farther you are from the equator, the shorter the window for effective synthesis.
Time of Day: UVB rays are strongest during the midday hours, typically between 10 a.m. and 3 p.m.. However, this is also when the risk of sunburn is highest. A useful rule of thumb is to look at your shadow: if it's shorter than you are, the sun is high enough for vitamin D production.
Skin Color (Melanin): Melanin, the pigment that determines skin tone, acts as a natural sunscreen. People with darker skin have more melanin and therefore require significantly longer sun exposure to produce the same amount of vitamin D as those with lighter skin. This is why darker-skinned individuals, especially those at higher latitudes, are at greater risk of vitamin D deficiency.
Age: As you get older, your skin becomes less efficient at producing vitamin D from sunlight.
Other Barriers: Clouds, smog, and even glass windows can block or filter the UVB rays necessary for vitamin D synthesis.

A Strategic Approach to Sun Exposure

Balancing vitamin D production with skin cancer prevention is critical. The goal is to obtain a small, safe dose of sun, not a tan. The Skin Cancer Foundation and other health bodies emphasize that excessive sun exposure is the most preventable cause of skin cancer.

Expose Bare Skin: For effective synthesis, you need to expose your bare skin—like your arms, legs, and back—to direct sunlight. Wearing clothing that covers most of your skin can hinder production.
Aim for Short Durations: Many health experts suggest 5 to 30 minutes of sun exposure to bare skin, two to three times per week, during the optimal midday hours. The exact duration depends on your skin type and location; lighter skin needs less time.
Time it Right: To minimize risk, some people opt for the early morning or late afternoon sun, although UVB is less potent during these times. For those seeking peak UVB, keep the duration short and protect your face and sensitive areas.
Cover Up and Use Sunscreen: After the recommended short, safe interval, apply a broad-spectrum sunscreen with an SPF of 15 or higher to all exposed skin. While sunscreen blocks UVB, the amount people typically apply still allows for some vitamin D production, and the protection from skin damage is paramount.

Compare: Sun Exposure vs. Supplements for Vitamin D


Feature	Sun Exposure	Supplements	Other Food Sources
Mechanism	Your body naturally synthesizes vitamin D from UVB rays.	Contains vitamin D2 or D3 for oral consumption.	Limited food types contain vitamin D naturally (e.g., fatty fish, egg yolks), or are fortified.
Production Control	Self-regulating; your body stops production to prevent toxicity. Affected by numerous external factors.	Doses are controlled and consistent, but high doses can cause toxicity.	Variable intake depending on diet, rarely sufficient alone.
Primary Risk	Skin cancer from overexposure to UV radiation.	Potential for toxicity if too much is taken over time.	Dietary factors may influence absorption.
Accessibility	Limited by geography, season, and climate.	Readily available year-round, regardless of location or weather.	Available year-round, but often not enough to meet full needs.
Recommendation	Safe, limited exposure can contribute to levels, but not a year-round solution for all.	Often necessary to ensure adequate vitamin D levels, especially in winter or for high-risk groups.	Include in diet to supplement other sources.

Alternative Sources of Vitamin D

For many, relying solely on sunlight for vitamin D is unrealistic or unsafe. This is especially true for those with darker skin, the elderly, or those living in higher latitudes. Thankfully, there are other reliable sources.

Dietary Sources: Few foods naturally contain significant vitamin D, but some, like fatty fish (trout, salmon, tuna), egg yolks, and beef liver, are good sources. Certain mushrooms also contain D2 when exposed to UV light.
Fortified Foods: Many common foods are fortified with vitamin D, including milk, plant-based milk alternatives, cereals, and orange juice.
Supplements: Vitamin D supplements are widely available and are a reliable way to ensure adequate intake, particularly during winter months or for those with specific risk factors. The two main forms are D2 (ergocalciferol) and D3 (cholecalciferol), with D3 often considered more effective. It is wise to consult a healthcare provider before beginning supplementation.

Conclusion: Striking a Healthy Balance

Learning how to expose to sun for vitamin D is an exercise in balance. While the sun offers a natural way to boost levels of this essential nutrient, it is not a risk-free method. A cautious approach involves brief, unprotected exposure to a limited amount of skin, particularly during peak UVB hours when the shadow rule is met. For consistent, reliable vitamin D levels, especially for high-risk individuals or during colder months, supplementation and a diet rich in fortified foods are often the safest and most effective options. Always prioritize sun safety to minimize the long-term risk of skin damage while still benefiting from the 'sunshine vitamin.' For more in-depth information on vitamin D's overall benefits and risks, the NIH Office of Dietary Supplements is a valuable resource.

A Quick Guide to Safe Sun Practices

Stay out of the peak sun. Avoid prolonged exposure between 10 a.m. and 3 p.m. when UV is strongest.
Go for shorter exposure times. Start with 5-10 minutes of unprotected sun exposure and increase gradually based on your skin type and location.
Wear a hat and sunglasses. Protect your face and eyes, which are especially vulnerable to UV damage.
Use sunscreen after brief exposure. Apply broad-spectrum SPF 15 or higher after your short, unprotected period for longer outdoor activities.
Consider your skin tone. Those with darker skin need more exposure time than those with lighter skin. Be patient and mindful of your skin's needs.
Don't rely on windows. Glass blocks the necessary UVB rays, so you won't produce vitamin D while indoors.
Know your alternatives. Incorporate fortified foods and supplements to ensure consistent vitamin D levels year-round, especially in winter.

Additional Resources

NIH Office of Dietary Supplements: Vitamin D Fact Sheet
The Skin Cancer Foundation: Sun Protection and Vitamin D
Centers for Disease Control and Prevention: Sun Safety Facts

Frequently Asked Questions

The best time is typically between 10 a.m. and 3 p.m., when UVB rays are most intense. A good sign is if your shadow is shorter than you are. However, be mindful that this is also when the risk of sunburn is highest, so brief exposure is key.

The duration depends on your skin type, location, and the time of day. Most experts suggest between 5 to 30 minutes of sun exposure to your arms, legs, and face, a few times a week. People with darker skin tones will need more time than those with lighter skin.

Yes. Melanin, the pigment responsible for darker skin tones, acts as a natural sunblock. This means people with more melanin need longer exposure times to produce the same amount of vitamin D, putting them at higher risk for deficiency.

Yes, some vitamin D is still produced. While high-SPF sunscreens are designed to block most UVB rays, most people don't apply them perfectly, allowing some UV light to reach the skin. The Skin Cancer Foundation affirms that daily sunscreen users can maintain vitamin D levels.

No. Standard window glass blocks the UVB rays that are necessary for your skin to produce vitamin D.

The primary risk is developing skin cancer from UV radiation damage. Excessive exposure, even without sunburn, can contribute to both melanoma and non-melanoma skin cancers. The key is balance and never tanning to increase vitamin D.

Alternatives like supplements and fortified foods are necessary during winter months in higher latitudes, for individuals with darker skin tones, for older adults whose skin is less efficient at production, and for those who cover up for religious or health reasons.