Michael Douglas loves Catherine Zeta Jones, but she has ''her own issues''.

The Hollywood couple's 13 year marriage has weathered Michael's throat cancer ordeal - which he was given the all-clear from in 2011 - and Catherine attending rehab for Bipolar II disorder twice, but friends say dealing with these things has taken its toll on their marriage, which they announced earlier this week they are taking a break from.

A source close to Michael told the Daily Mirror newspaper: ''It's very stressful. He loves her but she has her own issues.''

Catherine, 43, also found it difficult to deal with Michael's diagnosis and treatment for cancer, and wishes she could have done more to help him.

She has said in a previous interview: ''I haven't had to deal with anything like that before. I wasn't as strong as I thought I could have been.''

Other friends claim the pair - who haven't been pictured together since April - have clashed over their lifestyles, with Michael, 68, still keen to party while Catherine has found moving from Bermuda to the US in 2009 hard and prefers to stay at home.

A source told The Sun newspaper: ''They have grown apart -- but not in the way you'd expect, given the age gap.

''Michael loves the buzz of the city. He enjoys socialising and the finer things in life and has lots of showbiz mates. Catherine likes the countryside where she can ride horses, play golf and live a very quiet existence.

''He only moved to the countryside for her but in the end their health problems over the past few years took their toll and he had to escape.''

Michael is believed to have been staying in New York City in recent months, while Catherine has been at the couple's home in Bedford, Connecticut, where they raise their children Dylan, 13, and Carys, 10. Currently he is in Europe to attend the Deauville Film Festival in France.