12 June 2012 Last updated at 19:45 ET By James Gallagher Health and science reporter, BBC News
Lifestyle advice given to tackle male infertility may be futile and could delay other options, according to researchers in the UK.
Their study in the journal Human Reproduction said smoking, alcohol consumption and being obese did not affect semen quality.
However, they warned that avoiding them was still "good health advice".
Wearing boxer shorts rather than tighter underwear was linked to higher sperm levels.
Advice for doctors by the National Institute for Health and Clinical Excellence says men should be warned about the impact of smoking, drinking and taking recreational drugs on their sperm.
A study by researchers at the Universities of Sheffield and Manchester compared the lifestyles of 939 men with poor sperm quality with 1,310 men with normal sperm quality.
There is no need for them to become monks just because they want to be a dad
The study showed there was little difference in the number of mobile sperm between patients who never smoked and those who had a 20-a-day habit.
There was "little evidence" that recreational drug use, a high BMI or excessive alcohol consumption affected sperm quality.
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