[EvaH (OP)]

Philip asks:

Last week one of the interviewees was talking about vitamin D said the government recommendation was 400 units a day and that he takes 4000. My jar of tablets says each one is 12 μg. How many units is that?

Can you help?

[Bored chemist]

Assuming wiki has got it right
Conversion: 1 µg (of cholecalciferol/ergocalciferol) = 40 IU.
Or 25 ng per unit.

[set fair]

I would define it as a millionth of the amount of vitamin D that we should make/ingest annually but others think we can get away with less.

[Bored chemist]

I would define it as a millionth of the amount of vitamin D that we should make/ingest annually but others think we can get away with less.

That's a really stupid choice of unit, isn't it? Because it depends on how much sunshine you get (among lots of other things like body mass).