It comes down to more than that though. If you aren't happy (as in, happy in your current life, not hung up on jealousy, having a positive outlook...etc), it can influence you to make bad 'health' choices. We've all heard of comfort food, right?
Stress causes many health issues. On a larger scale, it can be attributed to quite serious conditions such as stomach ulcers and heart attacks. On a scale more close to home, it can cause headaches, fatigue, digestive symptoms (even symptoms similar to IBS) and a low-functioning immune system.
It's all very well to say stress causes all these things, but it's not like you can say 'avoid stress', like it's as easy as avoiding dairy or eggs.
We are all exposed to stress and stressful situations (for the moment I'm talking more mentally than physically). It isn't 'who has the least stressful life', it is 'who deals with their stress the best'?
Meditation can sound like a 'hippy word', but it can be as simple as being aware of your own thoughts and trying to channel them into calm, positive thoughts. When you find yourself obsessing and worrying over an assignment, an argument with someone or a deadline you need to reach, STOP. Take a deep breath. Ask yourself, 'what can I do about it?'. If the answer is nothing, then move on. What is the point of it taking up your time?
If you can think of something you can do to make the problem better, then do it! Work calmly towards your goal and know that you can achieve it. More ways of coping with stress can be found here, I would write about them but it's all been written before, by people who can tell you more than I can.