Happiness and success are subjective things. To some, a good life is embodied in healthy, caring and supportive relationships. To others, it might mean having nice things and the time to enjoy them. Or maybe it's a sense of being grounded and having the capacity to bounce back and thrive in spite of the pitfalls which are part of merely being human. Regardless of your definition, science has found that certain behaviors can markedly affect your quality of life.

1. Having more sex makes you better at your job.

Researchers at Oregon State University have found a correlation between a healthy sex life and a person's job satisfaction and engagement at the office. It turns out that sex initiates the release of dopamine, a neurotransmitter which activates the brain's reward center, as well as oxytocin, a neuropeptide associated with emotional bonding and attachment. And, the effects last well into the next day, meaning a better mood the morning after improves your job performance.

2. You can actually be biologically younger.

But, it's going to take work. Researchers at Brigham Young University have determined that people who work out regularly at high levels have telomeres--the nucleotide endcaps of chromosomes--which are nine years younger than those who just sit around. It's a matter of running 30 minutes or more at least five days a week. The findings may be related to previous studies which have shown that exercise suppresses inflammation and oxidative stress.

3. Invest in your friendships. They are incredibly important.

According to Neal Roese, professor of marketing at the Kellogg School of Management at Northwestern University, one of the biggest regrets people have about their lives involves their friendships--not having them, losing them, or having low quality relationships. So, while you may have 200 "friends" on Facebook, how many of these people would drive you to the airport, help paint your living room or meet you on a moment's notice to listen to you vent about your problems? If this is an area you need help, know this: You're going to have to get out of the house if you want to build new relationships.

4. Taking action can increase your confidence.

Katty Kay and Claire Shipman, authors of The Confidence Code, wrote a stellar article for The Atlantic on this subject. Highlighting a pile of studies which have found that a wide confidence gap exists between the sexes, they point out that success is just as dependent on confidence as it is on competence. Their conclusion? Low confidence results in inaction. "[T]aking action bolsters one's belief in one's ability to succeed," they write. "So confidence accumulates--through hard work, through success, and even through failure."

5. Playing with words can keep you mentally strong.

Researchers at the University of Exeter Medical School and Kings College London crunched online data provided by more than 17,000 people older than 50 and found a correlation between doing word puzzles and improved cognitive performance. They determined that people who do crossword puzzles, for example, have brains that function as if they are 10 years younger than their biological age, particularly when it comes to reasoning speed and short-term memory accuracy.

6. Take a break from your smartphone if you want to be sharp.

Your ability to think drops markedly when your smartphone is in reach, even if it's silenced or powered down. That's according to researchers at the McCombs School of Business at The University of Texas at Austin who studied nearly 800 smartphone users who took computerized tests which necessitated full concentration in order to score well. The tests were designed to measure cognitive capacity and participants were instructed to silence or turn off their smartphones and place them face down on the desk, in a pocket or personal bag or in another room. The people who kept their phones in another room significantly outperformed the ones who kept them nearby. Apparently, the notifications people get on their phones aren't the problem. Merely having a phone within reach makes it harder to focus because a percentage of the brain has to actively work to not pick up or use the device.

7. Getting adequate quality sleep is like winning the lottery.

A researcher at the University of Warwick in the United Kingdom found that improving your sleep quality and quantity is as good for health and happiness as winning the lottery. According to researchers, everyone on the planet should be logging at least seven hours of sleep a night. Here's how to get more of it.

8. Giving your time and money away will make you happy.

Americans who rate themselves as "very happy" volunteer an average of 5.8 hours per month, compared with those who describe themselves as "unhappy" and log only about 0.6 hours. That's according to researchers at the University of Notre Dame who also found that people who donate more than 10 percent of their incomes are less depressed than people who give less. Being generous emotionally also pays off--people who are available and hospitable to others are significantly more likely to be in excellent health.