Display Member since regsitered date

I would like to display a ‘Member since’ but can’t make the ‘registered’ field show up – I looked in the user table in php my admin and the user_registered field is filled in with a valid date-time stamp. But it won’t appear if I try to display it. The other fields work fine.

[users ID=XXX]
User: [user]
Contact: [user email]
Name: [user first_name]
Registered: [user registered]
[/users]