This is a limitation of the Windows operating system. Environment variables that are set from within a process, instead of being set through the control panel, are visible only to that process.
A possible workaround would be to use ActiveX functionality, as implemented in the attached file. Please note that setting a system-wide variable this way requires a restart in order for the changes to take effect.
As another possible workaround, Microsoft offers a tool called "setx" which allows you to set system-wide environment variables. This command is available in Windows versions later than Windows XP Service Pack 2 and Windows 2000.
Here is an example how to use it from within MATLAB:
>> !setx my_var some_value
This way of setting a system-wide environment variable does not require a restart of Windows or user re-logging on. However, note that if you use the Windows command window and
the "set" command to view the environment variables, you will need to restart the command window to see the change.