More than 70% of those voluntary gifts were donated by individuals and families. Even though donations dropped sharply during the Great Recession and have yet to fully recover, Americans still give away more than the entire gross domestic product of prosperous countries such as Israel and Denmark.

American generosity is internationally exceptional and generally amazes foreigners, especially those from the social democracies across the Atlantic.

As a European acquaintance once asked me, “What’s in it for you?”

A reasonable question. Leave aside for a moment the metaphysical rewards of giving; as a social scientist would say, they are “empirically untestable.” Here in this mortal coil, does giving boost our odds of living longer and healthier lives? Will it make us more attractive? If we fail to donate, will others think we were raised by wolves?

The answer to all these questions is “yes.” For starters, happiness and giving are strongly correlated. The University of Chicago’s General Social Survey shows that charitable givers are 43% likelier to say they are “very happy” than nongivers. Nongivers are a whopping 3.5 times more likely than givers to say they are “not happy at all.”

Skeptics will question the causality here. Does charitable giving make us happier, vice versa or both? Experimental studies hold the answer. In 2008, researchers from Harvard and the University of British Columbia found that the amount subjects spent on themselves was inconsequential for happiness, while spending on others yielded significant happiness gains.

Meanwhile, researchers at the University of Oregon attached fMRI scanners to participants and asked them to divide $100 between a food pantry and their own wallets. Choosing charity lighted up the nucleus accumbens, a brain center of pleasure and reward that also corresponds to pleasurable music, addictive drugs, and the bond between mothers and their children.

Giving improves our health, too. In a new study of more than 800 Detroit residents, a psychologist from the University of Buffalo found that volunteering significantly lowers the association between stressful life events and death.

Similarly, when researchers at Stanford University and the Buck Institute for Research on Aging tracked nearly 2,000 older Americans from 1990 to 1999, the researchers found that the dedicated volunteers among the group were 56% more likely to have survived through the study’s end than nonvolunteers in identical health. And it pays to start early: A report published in 2008 by the University of California found that altruistic teenagers are physically and mentally healthier late in their lives than their less generous peers.

Charitable giving is even good for our looks. In 2009, Dutch and British researchers showed female college students one of three videos featuring the same handsome actor. In the first, he gives generously to a beggar on the street; in the second, he hands over just a little money; and in the third, the man gives nothing. The more he gave, the more handsome he appeared to the women in the study.

This no doubt explains why men loosen their wallets when trying to impress women. A 1999 experiment from the University of Liverpool showed that eager men on first dates give significantly more to a panhandler than men who are ensconced in comfortable long-term relationships.

As remarkable as all this may seem, these findings meet with scholarly consensus, not controversy. Giving generously to the causes we value really does boost our well-being and our esteem in the eyes of others. Consider the science and ask yourself: Can you really afford not to give?

So, on behalf of my colleagues in America’s millions of nonprofits, voluntary organizations and houses of worship, I want you to know we’re here for you. We want to help you become healthier, happier and better looking. Preferably before the end of the calendar year.

Mr. Brooks is president of the American Enterprise Institute.