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Do You Have to Be in Direct Sunlight to Get Vitamin D & Maximize Its Benefits?

Do you have to be in direct sunlight to get vitamin D? Explore safe ways to get your dose and maximize its health benefits.

We all know how vital vitamin D is for health. We get vitamin D from certain foods, supplements, and—most importantly—sunlight. But with summer a distant memory for many of us, getting enough vitamin D from sunlight can feel like a challenge. Do you have to be in direct sunlight to get vitamin D? Or can you get enough by soaking up some rays while sitting in the shade or enjoying an overcast day? This article will answer that question and help you understand how to safely and effectively get enough vitamin D from sunlight to improve your overall health and well-being without risking sun damage. So, how to measure sun exposure?

SunSeek has a solution to help you achieve your vitamin D goals: our daily sunlight exposure tracker. This easy-to-use tool will help you monitor your vitamin D levels to determine how much sun exposure is enough for your health and when to start taking precautions to avoid sun damage.

How Do We Make Vitamin D From the Sun?

sunrise - Do You Have to Be in Direct Sunlight to Get Vitamin D

There’s a reason why vitamin D is nicknamed “the sunshine vitamin,” as the sun is the best natural source of vitamin D.

Vitamin D is a vital micronutrient many people lack. Its benefits include:

Healthy bones
Metabolic function
Cognition
Heart health
Immune health

The simplest way to get it is through moderate sunlight exposure.

Vitamin D and the Sun: How It Works

We synthesize vitamin D when our skin is exposed to UVB (ultraviolet B) rays from the sun (or artificial UVB lamps). For a quick nutritional biochemistry lesson, a form of cholesterol called 7-dehydrocholesterol in the plasma membranes of skin cells (epidermal keratinocytes and dermal fibroblasts) absorbs UVB photons upon sunlight exposure.

The Role of UVB and Sunlight in Vitamin D Synthesis: From Previtamin D3 to Its Active Form

Adding UVB causes 7-dehydrocholesterol to transform into an inactive form of vitamin D called pre-vitamin D3 or precalciferol. Previtamin D3 converts into vitamin D3 (cholecalciferol), which is then metabolized in the liver to 25-hydroxyvitamin D3 (the circulating form found in the blood), then in the kidneys to its biologically active form, 1,25-dihydroxyvitamin D3. As we don’t get much vitamin D from our food intake, sunlight is the primary method for boosting or maintaining its levels, and people who get more sun exposure have higher blood vitamin D levels than people who spend more time inside.

How Much Vitamin D Do You Make From the Sun?

The short (and annoying) answer is: it depends. As we’ll see in the next section, many factors can impact vitamin D synthesis, most of which are outside our control. Let’s look at some studies that have assessed vitamin D production from sunshine exposure. A study in Switzerland found that just 10-15 minutes of sun exposure in the spring and summer, with 22% of skin exposed, produced 1,000 IU of vitamin D. During these warmer seasons, the time between sunburn risk and producing 1,000 IU of vitamin D ranged from 9 to 46 minutes.

This means that some people are at a greater risk of developing harmful sunburns before they reach adequate vitamin D production. During the fall and winter, up to 6.5 hours of sun exposure (with 8-10% of the skin surface uncovered) was required to achieve the same vitamin D levels, which increases the risk of sunburn or sun damage.

Understanding Body Surface Area and Minimal Erythemal Dose (MED) for Optimal Vitamin D Synthesis

For reference, the face accounts for approximately 9% of the body’s surface, each arm is 9%, each leg is 18%, and the abdomen and back are 18% each. Sunnier environments accelerate vitamin D synthesis, allowing the body to produce ~1,000 IUs within just a few minutes. It’s generally recommended that you expose yourself to sunlight for 50% of the time it would take you to develop a mild sunburn or slight pinkness that remains 24 hours later—this is called the “minimal erythemal dose,” or MED.

The Impact of Full-Body UVB Exposure on Vitamin D Levels Compared to Supplements

Exposing the whole body (like in a bathing suit) to 0.5 MED of UVB radiation (meaning it did not cause sunburn) has been shown to synthesize 7,000 to 10,000 IU of vitamin D. As everyone’s MED is different, the time this takes would vary depending on how quickly you tend to burn. Research has shown that fair-to-medium-skinned adults in bathing suits who were exposed to 0.5 MED of UV radiation just once per week for 3 months increased their serum vitamin D levels by 125-200%. In comparison, adults who took 1,000 IU of supplemental vitamin D daily during that time increased their blood levels by about 50%.

Optimizing Vitamin D Production: The Balance Between Safe Sun Exposure and Avoiding Sunburn

This study in Australia found that summertime sun exposure for 2 to 14 minutes at noon (three to four times per week with 15% of the body exposed) produced up to 600 IU of vitamin D (the Recommended Dietary Allowance) in fair-skinned people. Sunburn was found to occur in as little as 8 minutes—again, meaning that some people might not get enough vitamin D without burning first. To circumvent this, some researchers recommend getting sunshine “little and often,” which could mean 5 minutes of exposure at a time, a few times daily.

Winter Sunlight vs. Supplements: How to Maintain Healthy Vitamin D Levels Year-Round

In the winter, when only your face and hands are exposed, it may take up to 6 hours of sun exposure during peak hours for your skin to produce sufficient vitamin D, so a vitamin D supplement is often recommended during the cooler months. It’s estimated that 5 to 15 minutes of sun exposure with 25% or more of your body exposed at least three times a week during peak hours (11 a.m. to 3 p.m.) is likely adequate to maintain healthy blood vitamin D levels. If you have dark skin, you may need up to 30 minutes.

Factors That Affect Vitamin D Synthesis

Geographic Location

People living in more northern latitudes farther away from the equator have lower exposure to the sun. This is due to something called the “solar zenith angle.” The solar zenith angle is the angle between the local zenith (directly above the point where you are on the ground) and the line of sight from that point to the sun. The higher the sun is in the sky and the closer to the equator you are, the lower the solar zenith angle.

How Latitude and Solar Angle Affect UVB Exposure and Vitamin D Production

As the solar zenith angle increases (when the sun gets further away from the highest point in the sky), the amount of UVB rays reaching the earth’s surface is reduced. At higher latitudes—which have a greater distance from the equator—more UVB radiation is absorbed by the ozone layer, meaning it’s less able to reach our skin. In general, the further you get from the equator, the lower the vitamin D status of that population.

At high latitudes (>40°), the sun does not provide any vitamin D during the winter, making vitamin D supplements, cod liver oil, or a focus on consuming fatty fish essential. For example, people living in Boston (42° North), Edmonton, Canada (52° North), Norway (60° North), and Ushuaia, Argentina (55° South) are all unable to produce significant amounts of vitamin D from the sun for 4 to 6 months of the year.

Skin Color and Type

How much vitamin D you make has a lot to do with your skin color and type.

Skin type is based on the Fitzpatrick scale:

Type I: The palest and whitest skin tone that always burns (and quickly) and never tans
Type II: Fair/white and usually burns; sometimes tans, but with difficulty
Type III: Medium, white/olive skin tone; sometimes mildly burns but gradually tans into an olive color
Type IV: Olive/moderate brown; rarely burns and tans easily
Type V: Brown/dark brown; very infrequently burns and tans very quickly
Type VI: Black/very dark brown; never burns and tans very quickly

How Melanin Affects Vitamin D Production, and Sun Exposure Needs for Darker Skin Types

People with Type IV (sometimes Type III) and above have more melanin in their skin, which helps to protect the skin against damage from excessive sun. Melanin absorbs UV rays, acting like an internal sunscreen. (This does not mean people with darker skin are immune to skin cancer!) While it’s helpful that people with dark skin types don’t burn as quickly, that also means that they don’t produce vitamin D as quickly. Some research suggests that people with darker skin need anywhere from 30 minutes to 2 hours longer in the sun than light-skinned people to get the same amount of vitamin D.

Season and Time of Day

Both the time of year and the time of day affect vitamin D synthesis, which is again related to the sun’s solar zenith angle. The solar zenith angle is increased during the early morning and late afternoon (when the sun is not directly overhead) and during the winter months. The best vitamin D synthesis comes midday, but peak hours are from 10 am to 2 pm. The UV Index needs to be over 3 for our skin to produce significant vitamin D, which often only occurs during these midday hours. In the summer, the peak hours might be extended. When the UV index is 3 or higher, these are the general recommendations for the maximum amount of time to expose unprotected skin:

Type I: 10 minutes
Type II: 20 minutes
Type III: 30 minutes
Type IV: 50 minutes
Type V and VI: 60 minutes

Midday summer sun exposure will produce the fastest and most significant vitamin D synthesis.

Clothing

The more clothing you wear or cover your body, the less surface area is exposed to the sun’s UVB rays. Although it seems straightforward, there are some caveats here, too. As you may know, if you spend a lot of time outdoors, some clothing is equipped with UPF (UV Protection Factor), while others are not. If you wear UPF clothing, UVB rays will not penetrate the clothing, and you will not get vitamin D under the covered areas.

Some fabrics do let through some UVB rays. For example, a 2014 study found that 100% cotton-knitted fabric allowed for a 15% transmittance of solar UV rays, leading to a slower rate of vitamin D synthesis with reduced sunburn risk. If you want to maximize your 5-30 minutes in the sun, take off as many clothes as reasonably possible (and appropriate!) to get the maximum amount of vitamin D synthesis.

Weight

Excess body weight may affect how the body synthesizes and stores vitamin D. Research has found that obese people have a 57% lower vitamin D synthesis after exposure to whole-body UV radiation and high-dose vitamin D supplementation compared to non-obese BMIs. Although the research isn’t conclusive, one reason might be that subcutaneous adipose tissue has lower expression of one of the enzymes needed to convert inactive vitamin D into its active form. This means that people with more adipose tissue (fat) may have trouble with the conversion process that fully activates vitamin D.

Genetics

Researchers have pinpointed several genes involved in the synthesis and transport pathways related to vitamin D metabolism. Alterations or variants in these genes may affect overall vitamin D status, including how it’s synthesized in the skin. One of the genetic variants involved in vitamin D synthesis is the gene DHCR7 (7-Dehydrocholesterol Reductase).

From our biochem lesson earlier, 7-dehydrocholesterol is the form of cholesterol in our skin that reacts with UVB rays to synthesize vitamin D. DHCR7 encodes for the enzyme that helps convert 7-dehydrocholesterol into cholesterol. People with elevated gene expression will have increased rates of this conversion, which reduces the availability of 7-dehydrocholesterol in the skin for UVB rays to interact with. Other genes may also be altered, including:

Those related to vitamin D receptors
Vitamin D binding proteins
Transport proteins
Cholesterol metabolism

Sunscreen Use

Some researchers think the rise in sunscreen use over the past 50 or so years is why vitamin D deficiency is so prevalent in modern society. Other researchers state that sunscreen typically does not significantly inhibit vitamin D synthesis (which may be in part because people apply sunscreen so poorly).

While sunscreen is undoubtedly essential to protect against skin cancer and sun damage, there is a middle ground many of us can take to optimize our vitamin D synthesis while still protecting ourselves. Most studies have used a lower SPF (like SPF 15), which still allows for some vitamin D production. It’s also important to note that only broad-spectrum sunscreen (that blocks both UVA and UVB rays) would affect vitamin D, as we only make it in our skin upon exposure to UVB.

The authors of a review in the British Journal of Dermatology conclude, “Judicious use of daily broad‐spectrum sunscreens with high ultraviolet (UV) A protection will not compromise vitamin D status in healthy people.” They also state that people using high-SPF sunscreens, protective clothing, or shade-seeking behavior are more likely to have compromised vitamin D status.

Balancing Sunscreen Use and Sun Exposure for Vitamin D Synthesis and Skin Protection

Other research states that sunscreens with an SPF of 30 will absorb approximately 95% of incident UVB radiation, reducing vitamin D production in the skin by about 95%. Overall, a moderate broad-spectrum sunscreen with higher UVA protection (~SPF 15) will likely not affect vitamin D synthesis, and daily sunscreen is always recommended to protect against skin cancer, skin damage, and premature aging.

That said, getting 5-30 minutes of unprotected sunlight exposure (depending on your skin type and propensity to burn) without sunscreen is the best way to raise vitamin D levels. If you are worried about premature aging, always apply sunscreen to your face and instead use your arms.

Do You Have to Be in Direct Sunlight to Get Vitamin D

Vitamin D is produced when ultraviolet rays from the sun, specifically UVB rays, hit the skin. Soaking up the sun is the best way to get enough vitamin D (while still wearing sunscreen, of course). But that's not easy during winter when even a short walk requires bundling up. It’s not as if we’re all collectively living in total darkness for months, though.

Most people still get plenty of indirect sunlight through windows, whether sitting at a strategically placed work-from-home desk or driving in the car. But if you rely on sunny windows to get vitamin D, your nutrient needs aren't exactly made in the shade. Doctors say you likely aren't getting enough—which is essential since being deficient in the nutrient is linked to a wide range of health problems.

Can You Get Vitamin D Through a Window?

Unfortunately, all four experts also say it’s impossible to get enough vitamin D through a sunny window; the glass blocks it. Dr. Tolliver explains that there are two types of ultraviolet rays: UVA and UVB. UVB rays lead to vitamin D synthesis. “Glass 100% blocks UVB rays—which is what you need to make vitamin D—while allowing in UVA rays,” Dr. Tolliver says. This means that if you sit near a sunny window all day, you get no vitamin D benefits and expose your body to harmful UV rays.

Takeaway tip: Anytime you’re exposed to sunlight, you should wear sunscreen—even indoors. Dr. Tolliver says this holds whether the sun is shining through a window in your car or your house; you are not getting any vitamin D benefits if a window is involved. Dr. Ordon reiterates that direct sun exposure, a.k.a. being outside in the sun, can help the body produce enough vitamin D. Still, for most people in the U.S., this is only possible during part of the year. For this reason, all the experts say it’s a brilliant idea to consider a vitamin D supplement.

Why Direct Sunlight Is Best For Vitamin D

Sitting near a sunny window might feel similar to getting outside, but it's no substitute for direct sun exposure. “Window glass absorbs all UVB radiation. You make no vitamin D [this way],” says Boston University Medical Center professor of medicine, physiology, and biophysics Michael Holick, M.D., Ph.D., who authored foundational research on vitamin D synthesis in the 1980s and has continued to lead the evidence-based conversation on vitamin D.

But as we alluded to before, even direct sun exposure isn't a foolproof way to produce vitamin D. As Holick explains, sunscreen and shade (which are essential for protection against other skin health concerns) will get in the way, and location, altitude, season, skin tone, age, and time of day have to be considered as well.

Who’s At Risk For Vitamin D Deficiency?

“For many people, sun exposure will simply not be enough to provide the vitamin D that your body needs,” says Victoria J. Drake, Ph.D.5, manager of the Micronutrient Information Center at the Linus Pauling Institute of Oregon State University. “Anyone who uses sunscreen to protect from the unwanted effects of sun exposure or spends a limited time outside, especially in the midday summer sun, may not be getting enough.”

Seasonal and Geographic Factors Limiting Vitamin D Production

She notes also that an SPF of just 15 can slash vitamin D production by over 90%.6 (To be clear: We are fans of thoughtful and intentional sun protection practices.) Season and location can limit vitamin D production even more severely. "If you are in Boston in winter and go outside for 15 minutes, you make zero vitamin D.

“You make no vitamin D from about November until the following March," Holick explains. "Unless you're going to be a lifeguard or a hunter-gatherer, you're not going to make very much vitamin D." (And even the lifeguard and forager aren't making vitamin D from the sun in the northern latitudes for several months of the year).

The Impact of Skin Tone on Vitamin D Production and Deficiency Risks

For people with darker skin tones, sunlight is an even less reliable source of vitamin D, as the presence of melanin naturally reduces vitamin D production in the skin. While 29% of U.S. adults are deficient in vitamin D, Black Americans are 15 to 20 times more likely to be highly inadequate [i.e., have serum 25-hydroxyvitamin D levels—that's 25(OH)D for short—below 10 ng/ml]. For reference, 25(OH)D is your serum biomarker (i.e., from a blood test) of vitamin D status in your entire body.

How to Safely Get Vitamin D From Sunlight

woman at a beach - Do You Have to Be in Direct Sunlight to Get Vitamin D

Bask In The Morning Sunlight: The Best Time to Get Vitamin D

We all know that sun exposure is good for vitamin D synthesis in the body. But do you also know that increased sun exposure, particularly exposure to Ultraviolet (UV) rays, raises the risk of skin cancer? The American Cancer Society (ACS) suggests that UV radiation exposure from the sun may be a significant risk factor for non-melanoma skin cancer, which occurs in 20–30 thousand people worldwide, as per the World Health Organization (WHO). If you do not bask in the sun, you also risk developing vitamin D deficiency. So, what do you do? Studies suggest morning sun exposure may be the best time to get vitamin D. Spending 10–15 minutes before 10 a.m. or after 4 p.m. may be the best time to minimize UV exposure.

Use Sunscreen Wisely to Protect Your Skin

Never compromise on sunscreen usage, especially when exposed to sunlight. Applying sunscreen after initial sun exposure is essential to protect against UV rays while allowing vitamin D synthesis.

Stay Hydrated While in the Sun

Sun exposure can also lead to dehydration, which can have serious consequences like:

Diarrhea
Nausea
Vomiting

This is why you must drink plenty of water to prevent the condition, which may also affect your body's ability to absorb vitamin D.

Consume Vitamin D-rich Foods

While sunlight is the best source of vitamin D, foods like fatty fish (salmon, mackerel), fortified dairy products, and egg yolks can also increase your body’s vitamin D levels. According to the Office of Dietary Supplements (ODS) of the National Institutes of Health (NIH), the recommended daily intake of vitamin D for most people is 15 mcg (600 IU). Infants up to 12 months require a slightly lower dose, while adults over 70 may benefit from a slightly higher intake of 20 mcg (800 IU) daily. Pregnancy and lactation stages also maintain the 15 mcg (600 IU) recommendation.

Vitamin D Supplements

Severe vitamin D deficiency can lead to complications. Symptoms often include:

Muscle pain
Bone pain
Joint deformities
Fatigue
Mood changes, like depression

In such circumstances, consulting a healthcare professional can help determine a personalized treatment plan comprising vitamin D supplements.

Download Our App to Track your Daily Sunlight Exposure Today

SunSeek helps you optimize your daily sunlight exposure by tracking and providing personalized recommendations based on your location, skin type, and health goals. The app combines real-time UV monitoring with guided outdoor activities to help you improve sleep, boost energy levels, and maintain optimal vitamin D levels throughout the year. By aligning your daily routine with natural light cycles, SunSeek makes harnessing sunlight's health benefits easy while ensuring safe exposure through personalized timing recommendations and cloud coverage forecasts.

Download our app now to track your daily sunlight exposure.