Generally speaking, 5 to 30 minutes of unprotected sun exposure to the hands, face, and arms at least three times a week between 11 a.m. and 3 p.m. is considered enough to keep blood vitamin D levels out of the deficient range (<30 nmol/L or <12 ng/mL).[1][2]
When determining how much sunlight you might need, there are two basic factors to consider:
- The UV index (a measure of UV radiation intensity, from 0 to 11+)
- Your Fitzpatrick skin type (a measure of how your skin responds to UV rays, from 1 to 6)
When the UV index forecast in your area is 3 or higher, people with Fitzpatrick skin types 1 or 2 should keep unprotected sun exposure to less than 10 minutes; skin types 3 or 4, less than 15 minutes; and skin types 5 or 6, less than 30 minutes.[3][4]
Fitzpatrick skin type scale
Keep in mind that longer periods of unprotected sun exposure don’t necessarily lead to higher vitamin D production, as the UVB rays will eventually cause the vitamin D in your skin to degrade to an inactive state.[5] This is a safety mechanism that helps protect your body against vitamin D toxicity.
Don’t stop using sunscreen just to get your vitamin D levels up — a balance can be struck here. In addition to an appropriate dose of sun exposure, you can increase vitamin D through diet and supplementation. Diet and supplementation strategies will be particularly important for those who live in areas of low sun exposure or at latitudes where the sun’s rays may not be as potent for vitamin D production (greater than 37 degrees north and south of the equator).
To summarize: Depending on the UV index and your skin type, 5–30 minutes of unprotected sun exposure to the hands, face, and arms at least three times a week between 11 a.m. and 3 p.m. should be enough to keep your vitamin D levels out of the deficient range. However, for people who live in northerly locations, have darker Fitzpatrick skin types, and/or lack sun exposure, supplementation may be required to maintain adequate vitamin D levels, as dietary sources of vitamin D tend to be inadequate.[10]
References
- ^Barbara B Shih, Mark D Farrar, Marcus S Cooke, Joanne Osman, Abigail K Langton, Richard Kift, Ann R Webb, Jacqueline L Berry, Rachel E B Watson, Andy Vail, Frank R de Gruijl, Lesley E RhodesFractional Sunburn Threshold UVR Doses Generate Equivalent Vitamin D and DNA Damage in Skin Types I-VI but with Epidermal DNA Damage Gradient Correlated to Skin DarknessJ Invest Dermatol.(2018 Oct)
- ^Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium, A Catharine Ross, Christine L Taylor, Ann L Yaktine, Heather B Del ValleDietary Reference Intakes for Calcium and Vitamin D
- ^Ann R Webb, Andreas Kazantzidis, Richard C Kift, Mark D Farrar, Jack Wilkinson, Lesley E RhodesColour Counts: Sunlight and Skin Type as Drivers of Vitamin D Deficiency at UK LatitudesNutrients.(2018 Apr 7)
- ^Ann R Webb, Andreas Kazantzidis, Richard C Kift, Mark D Farrar, Jack Wilkinson, Lesley E RhodesMeeting Vitamin D Requirements in White Caucasians at UK Latitudes: Providing a ChoiceNutrients.(2018 Apr 17)
- ^A R Webb, B R DeCosta, M F HolickSunlight regulates the cutaneous production of vitamin D3 by causing its photodegradationJ Clin Endocrinol Metab.(1989 May)
- ^Engelsen O, Kylling AFast simulation tool for ultraviolet radiation at the earth's surfaceOpt Eng.(2005 Apr)
- ^John C Dowdy, Robert M Sayre, Michael F HolickHolick's rule and vitamin D from sunlightJ Steroid Biochem Mol Biol.(2010 Jul)
- ^Vitaly Terushkin, Anna Bender, Estee L Psaty, Ola Engelsen, Steven Q Wang, Allan C HalpernEstimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudesJ Am Acad Dermatol.(2010 Jun)
- ^Ann R Webb, Ola EngelsenCalculated ultraviolet exposure levels for a healthy vitamin D statusPhotochem Photobiol.(Nov-Dec 2006)
- ^Whiting SJ, Green TJ, Calvo MSVitamin D intakes in North America and Asia-Pacific countries are not sufficient to prevent vitamin D insufficiency.J Steroid Biochem Mol Biol.(2007-Mar)