Do sunblocks prevent us producing enough Vitamin D?

I think that everything needs to be considered in a balance and there is a very good reason why sunblocks are recommended but common sense should be applied in using those as well.

I don't put the sunblock on before I go outside but I go first outside and only after being there for 10 or 15 minutes I apply the sunblock. I allow both some vitamin D synthesis in the skin as well as protecting myself from any excess in sunlight.