Don't worry, be happy.

That's not just good life advice, it could actually help you live longer.

It's no secret that most Americans see the glass as "half empty." More than half us describe ourselves as pessimists, and last year a record number of us reported feeling crummy about our lives.

But if you ever needed a little persuasion to look on the bright side, here it is: happier people tend to live longer, healthier lives.

But you don't need to take our word for it. As Jane Brody reports for The New York Times:

Studies have shown an indisputable link between having a positive outlook and health benefits like lower blood pressure, less heart disease, better weight control and healthier blood sugar levels.

Can Happiness Improve Your Health?

Whether you're living with a chronic condition already, or trying to stay healthy as you get older, there's evidence that a good mood is good medicine.

One study by the University of California gave a group of patients with HIV advice to "foster positive emotions."

Those patients had lower viral loads than other groups by the end of the study.

Part of the reason why is the positive group was better about following their doctor's orders; positive people tend to look after themselves, and adapt to changes more easily.

Can Happiness Make You Live Longer?

If you're hoping to stay alive for a long time, a positive outlook is a must-have.

Research proves patients with chronic conditions, including Type 2 diabetes and even AIDS, tend to live longer if they focus on positive emotions.

But just telling yourself to "cheer up" isn't good enough. Instead, there are some practical ways to boost your mood and keep yourself in good shape.

While people tend to think that they're either positive or negative by default, the truth is you can practice positivity like any other skill.

How To Develop A Positive Attitude

One of the most helpful ways to boost your mood is also the most fun: spend more time with friends.

Experts say that interacting with people you like and sharing positive feelings with them will make you happier.

Maybe it's also time to cut that negative person out of your life.

Next, take time each day to focus on gratitude.

Keeping a journal about one thing that made you smile each day will remind you what really matters.

Focus on the "here and now," not worrying about the future. And look for the silver lining in every minor "disaster" in your life.

Spend time doing silly things like watching fun movies, without worrying about being productive. And do good deeds for your friends and family.

Finally, it helps to smile more - even if you don't feel like it.

A University of Kansas study found that even "fake smiling" reduces your heart rate and blood pressure, so just keep looking on the bright side!

Improve you mood with 15 indoor plants that will encourage positivity and prosperity!

And practice these 12 ways to let positive energy take over your life!

[H/T: Mayo Clinic, Live Strong, Johns Hopkins Medicine]