Vitamin D in winter
Winter can reduce the UVB light available for skin to make vitamin D. Food and fortified products provide another source, while intake references account for limited skin production.
Why the season matters
Skin makes vitamin D when UVB light reaches it. Season, latitude, time of day, cloud cover, skin pigmentation and age all influence production. The same time outdoors does not give everyone the same amount.
These differences make a universal sun-exposure target unreliable. UV exposure also carries skin-cancer risk; vitamin D production is only one part of that picture.
Food provides another route
Oily fish naturally contain vitamin D. Some drinks and cereals have it added, but fortification varies by product and country. Check the specific food or label when comparing amounts.
What the daily reference means
EFSA sets an adequate intake of 15 µg per day for healthy people over one year, assuming minimal skin synthesis. It refers to total intake from food and supplements. The figure is a population reference; it does not establish an individual supplement dose.
References
Source-checked educational draft. Human editorial review pending.
NIH Office of Dietary SupplementsVitamin D: Fact Sheet for Health ProfessionalsSource accessed 2026-09-05European Food Safety AuthorityVitamin D: EFSA sets dietary reference valuesSource accessed 2026-09-04