Originally Posted by NatalieMojoHost

Ajax is a good solution if there are no load issues.

One caveat I'd point out there is that UPDATE queries tend to be quite heavy on a database, especially if you're dealing with hundreds of users online at any time, or updating on a large table. If the information does not need to be persistent, I would update something like a memcached key or redis object for each user, as those are much less intensive than running updates in SQL. Redis could be configured to save the changes to disk every X writes/minutes for some amount of persistence as well (though not as reliably as SQL, and then that's another database service you need to maintain/backup/etc) - just something to consider.
If it is a busy site, I think it would be better to use websockets for this kind of thing, and Redis to persist data.