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Vitamin A content of food in Japan vs USA
I'm sure that there are cultivation differences in different countries that affect the amount of nutrients in food, but according to the study linked to the first post I don't think it's the one to prove this. The reported amounts aren't because there are different amounts in the food but because it's calculated differently. From the report-
"The primary reason that~ the vitamin A values of vegetables and fruits are much higher in the United States than in japan, however, is due to the different manner in which the vitamin A activity from ~-carotene was calculated. The content of carotene in micrograms is divided by 0.6 to calculate vitamin A activity in international units in the United States, wh~reas. it is divided by 1.8 (0.6 X 3) in japan. Thus the vitamin A value of a given food in the U.S. food composition tables is three times higher than that in the Japanese .tables even if the same amount (micrograms) of carotene IS actually contained in the food.
So once again, it's that confusing way they calculate retinol and carotene if I'm reading the above correctly!
It seems like the report doesn't really have much use then. I don't understand why they bothered writing all that if that's the case they could have just indicated the conversion equation