Vitamin D from the Sun: How Much Time You Need and What Blocks It
Articles
Vitamin D from the sun is made in the skin by UVB radiation, and for most people it is the main source of this vitamin [1]. At European latitudes, people with fair skin need roughly 9 minutes of midday sun a day from March to September [2]. From October to March, UVB is too weak across much of Europe, and the skin makes almost no vitamin D [3]. This article explains how long to stay in the sun, what slows vitamin D production and when it makes sense to top it up.
What will you learn from this article?
- How the skin makes vitamin D from the sun
- How long to stay in the sun for vitamin D
- When the skin makes no vitamin D from the sun
- What affects vitamin D production in the skin
- When to top up vitamin D from food or supplements
- Key takeaways
How the skin makes vitamin D from the sun
The vitamin your skin makes in sunlight is vitamin D3, also called cholecalciferol. It forms when UVB rays of roughly 290 to 320 nm reach uncovered skin [1]. They convert 7-dehydrocholesterol into previtamin D3, which body heat turns into vitamin D3 [1].
This vitamin D is still inactive. The liver converts it to 25-hydroxyvitamin D (calcidiol), the form measured in blood tests. The kidneys then produce the active form, calcitriol [1].
Vitamin D contributes to normal absorption of calcium and phosphorus, to the maintenance of normal bones, teeth and muscle function, and to the normal function of the immune system. For the full picture, see our guide All about vitamin D.
How long to stay in the sun for vitamin D
The time you need depends on the season, the time of day, your skin tone and how much skin you expose. The best-studied recommendations for European latitudes come from the UK.
- Fair skin: about 9 minutes a day around midday from March to September. From June to August with forearms and lower legs uncovered, in the cooler months hands and face are enough [2].
- Darker skin: approximately 25 minutes a day over the same period [4].
- General guidance: some experts suggest 5 to 30 minutes between 10 a.m. and 3 p.m. at least twice a week, with the face, arms, legs or back uncovered [1].
Short exposures are enough, and your skin should never burn. After a certain time, previtamin D3 production levels off and further UV starts to break it down in the skin [5]. Staying out longer adds no vitamin D, it only raises the risk of skin damage.
When the skin makes no vitamin D from the sun
In winter the sun sits low in the sky. Its rays travel through a thicker layer of atmosphere, which absorbs most of the UVB [3].
A study in Boston (42° N) found that skin produced no previtamin D3 from November to February. In Edmonton, Canada (52° N), this period lasted from October to March [3]. The UK, Germany, Poland and Scandinavia all lie at or above 50° N, closer to Edmonton.
From October to March, most people in northern and central Europe make almost no vitamin D in their skin. In winter the body relies on the stores it built up in summer [2].
The time of day matters too. UVB is strongest around midday, roughly between 10 a.m. and 3 p.m. [1].
What affects vitamin D production in the skin
Even in summer, the amount of vitamin D your skin makes varies from person to person. The main factors are [1][6]:
- Latitude and season: the further from the equator, the shorter the period when vitamin D can form [3].
- Cloud cover and smog: both reduce the amount of UVB that reaches the skin [1].
- Skin tone: melanin absorbs UVB, so people with darker skin need more time in the sun [1][4].
- Age: an older study found that the skin of 77 to 82 year olds made less than half the previtamin D3 of teenagers' skin [7]. Newer research questions this difference in healthy older adults [8]. Older people do, however, usually spend less time outdoors.
- Excess weight: vitamin D is stored in fat tissue. After the same UVB exposure, blood vitamin D3 rose 57% less in people with obesity than in people of normal weight [9].
- Glass: window glass absorbs UVB. Sitting by an office window or in a car produces no vitamin D [6].
- Clothing and sunscreen: covered skin makes no vitamin D. The effect of sunscreen in everyday life is smaller than often claimed.
Does sunscreen block vitamin D?
In the lab, sunscreen with SPF 8 or higher greatly reduces vitamin D production [1]. In practice, people apply less sunscreen, miss parts of the body and do not reapply it [1].
A systematic review of 75 studies therefore concluded that sunscreen in real-life use barely lowers vitamin D levels [10]. An international expert panel added that sunscreens that prevent sunburn will not compromise vitamin D status in healthy people [11].
Do not skip sunscreen because of vitamin D. If you plan to spend longer in the sun, protecting your skin is the right choice.
When to top up vitamin D from food or supplements
The sun is the main source, but not the only one. Few foods contain vitamin D naturally, mainly oily fish such as salmon, mackerel or tuna, and to a lesser extent egg yolks [1].
Topping up vitamin D makes most sense:
- from October to March, when the skin makes almost none [3],
- if you spend most of the day indoors or in a car,
- with darker skin, at an older age or with excess weight [1][9],
- for children, covered in our article Vitamin D in relation to children's health.
The most reliable guide is your blood level of vitamin D. Ask your doctor for a test, ideally at the end of summer. How to set the dose based on the result is explained in Vitamin D: Proper Dosage, Benefits, and What Affects Your Levels.
Our Vitamin D3 2000 IU contains cholecalciferol from lichen, the same form your body makes in sunlight. We recommend taking it together with vitamin K2. Both are combined in one product in our Vitamin D3 + K2 liquid. Why the source matters is explained in Differences Between Plant-Based and Animal-Derived Vitamin D.
Key takeaways
Vitamin D forms in the skin only with UVB: the skin makes it from 7-dehydrocholesterol, and the liver and kidneys then activate it.
Short midday sun is enough: fair skin needs about 9 minutes a day from March to September, darker skin around 25 minutes.
No vitamin D in winter: across northern and central Europe, the skin makes almost none from October to March.
Glass blocks UVB: you make no vitamin D by a window or in a car.
Keep using sunscreen: in real-life use it barely lowers vitamin D levels.
Sources:
[1] National Institutes of Health, Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
[2] Webb AR, Kazantzidis A, Kift RC, et al. Meeting Vitamin D Requirements in White Caucasians at UK Latitudes: Providing a Choice. Nutrients, 2018;10(4):497. https://doi.org/10.3390/nu10040497
[3] Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3. J Clin Endocrinol Metab, 1988;67(2):373–378. https://pubmed.ncbi.nlm.nih.gov/2839537/
[4] Webb AR, Kazantzidis A, Kift RC, et al. Colour Counts: Sunlight and Skin Type as Drivers of Vitamin D Deficiency at UK Latitudes. Nutrients, 2018. https://www.researchgate.net/publication/324431700_Colour_Counts_Sunlight_and_Skin_Type_as_Drivers_of_Vitamin_D_Deficiency_at_UK_Latitudes
[5] Webb AR. Who, what, where and when: influences on cutaneous vitamin D synthesis. Progress in Biophysics and Molecular Biology, 2006;92:17–25. https://ec.europa.eu/health/scientific_committees/scheer/docs/sunbeds_co152j_en.pdf
[6] Holick MF. Environmental factors that influence the cutaneous production of vitamin D. Am J Clin Nutr, 1995. https://pubmed.ncbi.nlm.nih.gov/7879731/
[7] MacLaughlin J, Holick MF. Aging decreases the capacity of human skin to produce vitamin D3. J Clin Invest, 1985;76(4):1536–1538. https://pmc.ncbi.nlm.nih.gov/articles/PMC424123
[8] Comparative Study of Healthy Older and Younger Adults Shows They Have the Same Skin Concentration of Vitamin D3 Precursor, 7-Dehydrocholesterol, and Similar Response to UVR. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11053405/
[9] Wortsman J, Matsuoka LY, Chen TC, Lu Z, Holick MF. Decreased bioavailability of vitamin D in obesity. Am J Clin Nutr, 2000;72(3):690–693. https://pubmed.ncbi.nlm.nih.gov/10966885/
[10] Neale RE, Khan SR, Lucas RM, et al. The effect of sunscreen on vitamin D: a review. British Journal of Dermatology, 2019;181(5):907–915. https://pubmed.ncbi.nlm.nih.gov/30945275/
[11] Passeron T, Bouillon R, Callender V, et al. Sunscreen photoprotection and vitamin D status. British Journal of Dermatology, 2019;181(5):916–931. https://onlinelibrary.wiley.com/doi/10.1111/bjd.17992
