Vitamin D is made by the sunlight shining directly on your skin (no sunblock or clothing). Sunshine contains UVA and UVB light. UVB light reacts with molecules in the body to make vitamin D.
Vitamin D levels are measured by a blood test. They measure 25 hydroxy vitamin D (25(OH) vitD). The UK adequate level of 25(OH)VitD is anything more than 50 nmol/L.
Things that affect vitamin D production from sunlight
- Season (summer more sunlight)
- Time of day (sun is most intense around midday)
- Latitude (closer you are the the equator the more intense the sunlight)
- Altitude (higher altitude, thinner atmosphere, more UVB light)
- Air pollution (high pollution can block UVB light)
- Skin pigmentation (lighter skin absorbs more sunlight, darker skin absorbs less sunlight)
- Sunscreen use (blocks sunshine)
- Sunlight passing through glass and plastic (glass and plastic blocks UVB rays of sunlight)
- Ageing (as you age your skin is less able to make vitamin D from sunlight)
So, how much vitamin D does the body make from sunlight?
It depends on the factors listed above.
A paper from 2024 by Kift and Webb says that the amount of time spent in the sun at midday is not prescriptive and it will range from around 3 minutes for white skin and 15 minutes for black skin. However, these numbers were to maintain current vitamin D levels, not to increase or decrease them.
An earlier UK study from 2018 looked at finding out how many minutes of sunlight you would need to meet vitamin D targets all year round without needing to increase the amount of vitamin D from your diet. They used previous data from studies conducted in Greater Manchester where they measured sunlight exposure on people aged from 20-60 and used climate modelling of the UV radiation in the UK.
They found out that for a white caucasian in the UK to get enough vitamin D from sunshine so it would last the whole year at the level of more than or equal to 25 nmol/L they would need:
Amount of time in the sun: nine minutes of sunlight (white caucasian, people with darker skin would need longer).
March to September:
daily, at lunchtime between the hours of 12pm- 2pm
direct sunlight (no shade), face, hands, Lower legs and forearms exposed
October to April
Daily, at lunchtime between the hours of 12pm-2pm
direct sunlight (no shade), face and hands exposed
However, the results were theoretical as it shows what could be possible if someone did decide to try it out. At the time the paper was published in 2018 the lower level for Vitamin D adequacy was 25 nmol/L according to the Scientific advisory Committee on Nutrition. Now in 2024 the adequate range is anything above 50 nmol/L. In the paper they did mention that there was a lot of variation as to what level of 25 (OH)VitD is adequate. However, from the study I am not sure how long you would have to spend in the sun to achieve and maintain a current adequate level of 50 nmol/L of 25(OH)VitD as this was not explored.
It is important to get enough vitamin D whether that is from foods, supplements or sunshine. Lifestyle changes where people spend more time indoors, wearing clothes that cover most of your skin can inhibit the production of vitamin D. Be aware that spending too long in the sun without protection can lead to sunburn and skin damage. So it is a balance between getting enough sunlight on your exposed skin but not too long so you get sunburn. Therefore, getting vitamin D from a variety of sources i.e. food and supplements and using sunlight to help maintain vitamin D levels would be an option.
This is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other healthcare professional. If you have any concerns about your general health, you should contact your local healthcare provider
References
Kift, R., Rhodes, L. E., Farrar, M. D., & Webb, A. R. (2018). Is Sunlight Exposure Enough to Avoid Wintertime Vitamin D Deficiency in United Kingdom Population Groups? International Journal of Environmental Research and Public Health, 15(8), 1624. https://doi.org/10.3390/ijerph15081624
https://www.mdpi.com/1660-4601/15/8/1624
Webb, A. R., Kazantzidis, A., Kift, R. C., Farrar, M. D., Wilkinson, J., & Rhodes, L. E. (2018). Meeting Vitamin D Requirements in White Caucasians at UK Latitudes: Providing a Choice. Nutrients, 10(4), 497. https://doi.org/10.3390/nu10040497
Wacker M, Holick MF. Sunlight and Vitamin D: A global perspective for health. Dermatoendocrinol. 2013 Jan 1;5(1):51-108. doi: 10.4161/derm.24494. PMID: 24494042; PMCID: PMC3897598.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3897598
SACN
Vitamin D and Health, 2016, Scientific advisory Committee on Nutrition,
BNSSG (Bristol North Somerset and South Gloucestershire) Adult Guidelines for Vitamin D Deficiency
https://remedy.bnssg.icb.nhs.uk/media/rorpnazk/bnssg-vitamin-d-guidelines-2024.pdf
Feb 2024, accessed on 02/01/2025.
Kift, R. C., & Webb, A. R. (2024). Globally Estimated UVB Exposure Times Required to Maintain Sufficiency in Vitamin D Levels. Nutrients, 16(10), 1489. https://doi.org/10.3390/nu16101489
Everything you need to know about Vitamin D, Nutrition made simple, 11/11/2024, accessed on 02/01/2025. https://youtu.be/C8svz186aE4?si=4yZ1PipyZ2q5OHYa
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