Accessing converted C++ class from python is 10-20 times slower

What is boost python actually doing when accessing a C++ class field from python. I could live with the overhead from calling functions but just accessing int/bool fields is 10-20 slower than a native python class.

Tested this by making two identical classes one in native python one in C++ and accessing a single integer field. Access in the C++ class seems to be 10 times slower. Can I do anything to improve this ?