Vitamin D and Sun Exposure: What You Need to Know to Optimize Your Levels
Discover the best time to sit in the sun for maximum absorption of vitamin D. Get answers to questions about effective sun exposure times and how to safely boost your vitamin D levels.
Published January 4, 2024.
While it's possible to get your daily dose of vitamin D from the foods you eat, very few foods are naturally rich sources. Instead, your body makes most of its vitamin D from sunshine. Known as "the sunshine vitamin,” vitamin D provides several important benefits to our bodies.  Let's delve into why it is so important, how much sun exposure is needed for vitamin D, and what you can do to optimize production and absorption.
» Some foods do contain vitamin D! Discover 10 vitamin D-rich recipes.
Why is vitamin D so important?
Your body naturally makes vitamin D when your skin is exposed to sunlight. The form of vitamin D that you get from the sun is called D3 (cholecalciferol), which is derived from cholesterol.
If you don’t go outside and get enough vitamin D sunshine time and expose your skin to the sun, it may result in low vitamin D. If you don’t get enough vitamin D, it can affect the way you feel and how well you perform.
The recommended daily intake of vitamin D is 20 mcg (800 IU) for adults and children age 4 years and older—and if your vitamin D levels are low, you may need to take even more. 
» Discover the importance of blood testing for vitamin D
The importance of vitamin D for athletes
Vitamin D is also crucial for athletes because it plays a vital role in various aspects of athletic performance along with overall health. Specifically, vitamin D helps to:
- Increase bone health along with the help of calcium
- Increase muscle mass and strength
- Increase the size and number of the muscle fibers that are used for short bursts of speed and power
- Improve lower body strength
- Build strength in your legs (along with calcium)
- Regulate the immune system and protect against certain diseases
- Prevent falls 
The only way to know whether your vitamin D levels are adequate is to have your blood levels checked. InsideTracker blood analysis includes vitamin D and will tell you not just whether your levels are normal but whether they are optimal to promote a healthy body and life.
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What is the best time to sit in the sun for vitamin D?
It's estimated that we should get more than 90 percent of our vitamin D through daily sun exposure. 
According to the National Institutes of Health, between 5 and 30 minutes of sun exposure to your unprotected face, arms, legs, or back between the hours of 10 a.m. and 3 p.m., two to three times every week is enough for your body to produce all of the D3 it needs. 
» Learn about vitamin D for daylight savings
5 factors affecting vitamin D absorption
The amount of vitamin D you get from exposing your bare skin to the sun and how much skin needs to be exposed for vitamin D depends on several factors. They are:
1. Where you live
The closer to the equator you live, the easier it is for your body to synthesize vitamin D from the sun’s rays all year round.
For instance, if you live at a northern latitude like Anchorage, Alaska, your body would create less vitamin D during the winter than someone who lives in Miami because Florida has more exposure to UVB rays that are necessary to produce vitamin D. 
2. How much skin you expose
If you wear clothing that covers most of your skin, you may be at risk for vitamin D deficiency. This also means that people who train indoors during winter may have to dig into their bodies’ vitamin D stores if they don't consume enough, increasing their risk for deficiency.
» Are you an athlete? Discover why you should pay attention to vitamin D
3. The color of your skin
People with darker skin may also have trouble synthesizing vitamin D from the sun. The pigment melanin, more prevalent in people with darker skin, reduces your body’s ability to make vitamin D in response to sunlight exposure. 
Essentially, this means that people who have pale skin produce vitamin D more quickly than people with darker skin.
Skin-color typology is generally arranged into the following categories:
- Type I – White; very fair; red or blond hair; blue eyes; freckles
- Type II – White; fair; red or blond hair; blue, hazel, or green eyes
- Type III – Cream white; fair; with any eye or hair color; very common
- Type IV – Brown; typical Mediterranean Caucasian skin
- Type V – Dark Brown; mid-eastern skin types
- Type VI – Deeply pigmented; commonly found in individuals with African ancestry
What skin color absorbs the most vitamin D?
In the context of vitamin D production, if you have skin type I to III, you produce vitamin D more quickly than if you have skin type IV to VI.
A dark-skinned person might need 10 times more sun exposure than a lighter-skinned person to produce the same amount of vitamin D.
A good rule of thumb is to get half the sun exposure it takes for your skin to turn pink to get your recommended amount of vitamin D. After you have exposed your skin for enough time, cover up with clothing and go back into the shade.
4. The time of year and day
When the rays of the sun enter the Earth’s atmosphere at a steep angle, UVB rays are blocked. This occurs during the early and later parts of the day and most of the day during the winter.
Which time sunlight is good for vitamin D?
If you want to increase your vitamin D, expose your skin to the sun closer to midday to allow for maximum production. However, relying on sunlight during the winter months may not be enough to meet your needs.
5. Which season it is
Americans’ vitamin D levels vary throughout the year, peaking in August and receding around February. In general, vitamin D levels have been shown to be the lowest during the winter months. 
In the summer, when the Earth rotates, the angle of the sun hitting the atmosphere is optimized for vitamin D production because more UVB reaches the places far away from the equator.
Can you get vitamin D on a cloudy day?
Cloudy weather can also be problematic because fewer UVB rays reach your skin on cloudy days.
» Do you have trouble sleeping? Check out how vitamin D can improve sleep
Does sunscreen block vitamin D?
Sunscreen can block vitamin D production. If you want your skin to absorb the UVB rays necessary to synthesize vitamin D3, you can’t wear sunscreen. Studies have found that sunscreens with sun protection factor (SPF) 8 or higher block our skin’s ability to produce vitamin D from sunlight by as much as 95 percent. 
Sunlight, vitamin D, and the risk for skin cancer
You shouldn't overdo your sun exposure due to the risk of skin cancer. Because of the dangers of excess sun exposure, you might want to talk to a physician to see if taking a supplement is the right choice. In the case of supplements, vitamin D is available in two forms: D2 and D3.
Since most steps involved in the metabolism of vitamin D2 and D3 are nearly identical, the two forms have traditionally been regarded as equivalent. While nutritional doses of D2 and D3 are equivalent, high doses of vitamin D2 are less potent.
Basking in the afterglow
If you go outside daily and have reasonable exposure to the sun, your vitamin D levels should be fine. But the only way to be sure is to get your blood tested. InsideTracker will measure your vitamin D levels and show you your optimal range based on age, gender, ethnicity, and athletic activity.
The 25-hydroxy vitamin D test is the most accurate way to measure how much vitamin D is in your body. It also tells you how to improve if they are out of range. Since so many of us have low levels of vitamin D, it is better to be safe than sorry!