Stress at work is not necessarily a bad thing. Most people function better under some amount of stress and pressure from deadlines - it often brings out the best in us.
But prolonged stress and long hours at work signal an undesirable situation that will have negative health effects on us. One very useful way to counter stress at work is to effectively delegate tasks to subordinates, allowing one to prioritise time towards higher-level strategic decision-making. Needless to say, the effectiveness of any delegation depends on the capability of subordinates and how much you trust them to make the right decisions with minimum intervention from you. Engaging in hobbies outside work is another effective means of relieving stress.
For example, I enjoy fishing, fresh and saltwater. I'm not your regular weekend angler but a fairly intense enthusiast who analyses fishing methods, water temperatures, feeding habits, different types and colour of bait/tackle, etc etc. I read widely and treat it as a challenging art form - how to locate and entice fish to take my bait. The point is, one has to totally engage and immerse oneself into a hobby for it to be effective as a stress reliever.
The ultimate goal is for the mind to be so totally immersed that you forget about work completely, for a short duration. It can even be something as fun as a family vacation, but the criteria must be total immersion - no emails, no texts/phones, no office contact.