Stress leads to the release of chemical by-products called free radicals which damage sperm. Stress at work or home leads to the release of adrenalin and other hormones which can restrict blood flow to the testes and inhibit sperm production.
Acute stress has major impact on the volume and number of sperm and chronic stress is also implicated. Even the stress of frequent flying has been found to lower sperm counts. De-stressing and increasing anti-oxidants in the diet have been statistically and clinically shown to be effective in improving sperm quality