The version of sudo that ships with Debian by default resets the
environment, as described by the "env_reset" flag in the sudoers file.

This implies that all environment variables are removed, except for
HOME, LOGNAME, PATH, SHELL, TERM, DISPLAY, XAUTHORITY, XAUTHORIZATION,
LANG, LANGUAGE, LC_*, and USER.

In case you want sudo to preserve more environment variables, you must
specify the env_keep variable in the sudoers file. You should edit the
sudoers file using the visudo tool.

Examples:
Preserve the default variables plus the EDITOR variable:

    Defaults env_keep+="EDITOR"

Preserve the default variables plus all variables starting with LC_:

    Defaults env_keep+="LC_*"