A report in the journal Fertility and Sterility (March, 2015) reported on 501 couples trying to conceive for a year. Thirteen percent of men who reported heavy work related activity had lower sperm counts compared to 6% of men who reported no exertion. Other work related exposures such as shift work night work, vibration, heat, noise, or prolonged sitting did not appear to have an effect.
The study also looked at the impact of certain medical heath issues and their relation to fertility. Among men who had received a diagnosis of high blood pressure, diabetes or high cholesterol, only those with hypertension had an increased risk of abnormal sperm morphology (shape) compared to men who repotted no high blood pressure. Furthermore, only 7% of men who took no medications had sperm counts below 39 million, compared with 15% of those who reported taking two or more medications. Authors note the result should be interpreted with caution.
In my own practice, I have seen patients with a variety of medical conditions and work related stress. I can say that I have seen improvement in parameters on semen analysis with the control of certain health issues such as diabetes. For those with work related stress, I have found a lack of sleep to be a frequent co factor. For my patients with morbid obesity, weigh loss can also sometimes help improve fertility.