[mpol]

Some differences that might play a role, but I have no real idea.

In the Netherlands cheap supermarket pizzas often have more fake cheese than real cheese. I can imagine that might mean less lactose, but maybe something in the fake cheese is giving you problems.

In the Netherlands most milk is pasteurized. I can imagine this is the case in the US too. In the Netherlands there is a special protected branding of cheese that is not pasteurized (boerenkaas). Pasteurizing milk reduces the calcium level. I can imagine Italians might prefer using unpasteurized milk products more than people in other countries.