Everyone knows that exercise is good for your body - but did you know that it's important for your mental health, too?

Scientists have discovered that exercise makes your brain release chemicals that make you feel good - the same chemicals that you get from antidepressants. For mild depression, research shows that physical activity can be as good as antidepressants or psychological treatments like cognitive behavioural therapy (CBT).

How much exercise? 

For good mental health, you should aim to do at least 30 minutes of moderate exercise, five days a week. Don't panic - this isn't as bad as it sounds! The key word here is moderate.

Moderate exercise means you're working hard enough to raise your heart rate and break a sweat, but you can still talk. It could include things like:

• walking the dog
• riding your bike
• skateboarding or roller-blading
• walking to school or work 

You can do it as one 30-minute session, or break it up into shorter 10- or 15- minute sessions. Choose something you enjoy - if you hate it, you won't stick to it. Find something that fits into your day and is right for you.

Of course, when you're feeling down, exercise is often the last thing you feel like doing. That's why it's useful to exercise with a friend, so you can motivate each other. The companionship is often as important as the exercise. Set goals and measure your progress, so you can see the difference it makes.