Do you need vitamin D in winter?
What the research found, how to do it, and every source the episode cites.
The verdict
Yes, in weak sun.
- When
- you eat breakfast
- Then
- take 10 µg of vitamin D
§ 01 · The protocol
§ 02 · Transcript
- The question
Do you need vitamin D in winter?
- How it works
Your skin makes vitamin D from sunlight. But in winter, the sun sits too low, and your skin makes next to none. The further from the equator, the longer this gap lasts. Athens gets two months of it, and Britain five. So the vitamin D in your blood keeps falling. In winter, nearly forty percent of British adults drop below the minimum level UK experts set. That matters, because vitamin D contributes to the maintenance of normal muscle function.
- The research
Winter trials tested how much you need. About ten micrograms a day kept almost everyone above that level.
- The protocol
Here's what to do. If you're an adult, take ten micrograms a day through autumn and winter. Too much can harm you, so never go over a hundred micrograms a day. If you have a health condition, ask your doctor first.
- The verdict
So yes, you need it when your winter sun is weak. Make it a habit, and track it with Anvilus.
§ 03 · In the sources' words
“The average daily vitamin D intake required to maintain serum 25(OH)D concentration ≥ 25 nmol/L in winter by the majority (97.5%) of the population was estimated to be around 10 µg (400 IU).”
“Vitamin D contributes to the maintenance of normal muscle function”
“Vitamin D contributes to the normal function of the immune system”
“In the UK, summer sunlight contains enough UVB for vitamin D synthesis but the small amount of UVB in winter sunlight means that vitamin D synthesis is negligible from at least October through early March (Webb et al., 1988) and serum 25(OH)D concentrations decline throughout the winter.”
“The “vitamin D winter” lasted for two months in Thessaloniki in Northern Greece and Athens, but was absent in Crete”
“The proportion with plasma 25(OH)D concentration < 25 nmol/L in winter was: children (4-10y), 31%; older children and adolescents (11-18y), 40%; adults aged 19-64y, 39%; and adults aged ≥ 65y, 29%.”
§ 04 · Sources
- Scientific Advisory Committee on Nutrition (SACN). Vitamin D and Health. Public Health England, 2016 (UK government expert committee review; dietary reference values set from winter dose-response RCTs in adults at 51-60° N)
- NHS. Vitamin D (UK government advice on vitamin D supplements)
- EU Register on nutrition and health claims, vitamin D entries, authorised by Commission Regulation (EU) No 432/2012 (EFSA Journal 2010;8(2):1468)
- O'Neill CM, Kazantzidis A, Ryan MJ, et al. Seasonal changes in vitamin D-effective UVB availability in Europe and associations with population serum 25-hydroxyvitamin D. Nutrients 2016;8(9):533 (modelled UVB, 2003-2012, 35-69° N; EU FP7 ODIN-funded)
- Demay MB, Pittas AG, Bikle DD, et al. Vitamin D for the prevention of disease: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 2024;109(8):1907-1947 (recommendations as published by the Endocrine Society)
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