Just 14 seconds of UV-B on sliced carrots
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Similar to the short time to greatly increase vitamin D in Mushrooms
this is probably vitamin D2 not vitamin D3
They do not appear to mention the IR of vitamin D before or after
Note: can also triple the vitamin D in eggs by increasing the amount of vitamin D in the chicken feed
It appears that you could then get 600 IU of vitamin D ( the RDA recommended in Nov 2010) with just 2 eggs.