Stevek76 wrote: It's not as if you get no vit D in the winter, it's that most people in normal times are stuck indoors for most of the daylight hours and the only significant diet sources are near enough just 'fatty' fish.
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in the UK and at other similar latitudes, you make virtually no Vitamin D from sunlight even if you are outdoors all day on a sunny day in winter with lots of exposed skin.
Dietary sources provide minimal levels and probably not enough to reach sufficiency.