As we approach year’s end, your mailbox is filling up with fundraising appeals from various charities and causes, hoping to capitalize on your holiday cheer — or at least, your effort to avoid a bit of 2007 income taxes through deductible contributions.

This is not a false hope: Americans gave nearly $300 billion away last year, and some charities claim to collect as much as a quarter of their annual contributions in the month of December alone. But there is one special reason to give, beyond the noble goals of helping your favorite charity and beating back the voracious taxman. It is that your gifts will give you a happier new year.

It is a fact that givers are happier people than non-givers. According to the Social Capital Community Benchmark Survey, a survey of 30,000 American households, people who gave money to charity in 2000 were 43% more likely than non-givers to say they were “very happy” about their lives.

Similarly, volunteers were 42% more likely to be very happy than non-volunteers. It didn’t matter whether gifts of money and time went to churches or symphony orchestras — givers to all types of religious and secular causes were far happier than non-givers.

People who give also are less sad and depressed than non-givers. The University of Michigan’s Panel Study of Income Dynamics reveals that people who gave money away in 2001 were 34% less likely than non-givers to say that they had felt “so sad that nothing could cheer them up” in the past month. They were also 68% less likely to have felt “hopeless,” and 24% less likely to have said that “everything was an effort.”

The happiness difference between givers and non-givers is not due to differences in their personal characteristics, such as income or religion. Imagine two people who are identical in terms of income and faith — as well as age, education, politics, sex, and family circumstances — but one donates money and volunteers, while the other does not. The giver will be, on average, 11 percentage points more likely to be very happy than the non-giver.

Giving goes beyond formal gifts of money and time, of course. Much of the way we serve others is less formal, or with other resources of value in our lives. One particularly visceral kind of giving involves our blood, which a bit over 15% of Americans donate at least once each year. If anything, this kind of charity is even more strongly associated with happiness than traditional gifts.

The National Opinion Research Center’s General Social Survey tells us that in 2002, 43% of the American adults who gave blood two to three times during the year said they were very happy versus only 29% of those who did not give blood, but were very happy.

We see the same pattern with many informal and nontraditional types of charity: giving to a homeless person on the street, giving directions to a stranger on the street, and so forth — it is all associated with higher levels of life satisfaction.

Of course, it might not be that giving increases our happiness, but rather that our happiness increases the likelihood that we will give. Everyone prefers to give more when they are happy. Researchers have investigated this by conducting experiments in which people are queried about their happiness before and after — sometimes long after — they participate in a charitable activity, such as volunteering to help children or serving meals to the poor. The result is clear that giving has a strong, positive causal impact on our happiness.

A number of studies have researched exactly why charity leads to happiness. The surprising conclusion is that giving affects our brain chemistry. For example, people who give often report feelings of euphoria, which psychologists have referred to as the “Helper’s High.” They believe that charitable activity induces endorphins that produce a very mild version of the sensations people get from drugs like morphine and heroin.

Charity also lowers the stress hormones that cause unhappiness. In one 1998 experiment at Duke University, adults were asked to give massages to babies — the idea being that giving a baby pleasure is a compassionate act with no expectation of a reward, even a “thank you” — in return. After they performed the massages, the seniors were found to have dramatically lower levels of the stress hormones cortisol, epinephrine, and norepinephrine in their brains.

The bottom line from all the research on giving is that it is not just good for your favorite cause; it’s good for you, too. For relief from stress and depression, it’s probably more cost-effective than whatever your doctor might prescribe. For getting a little high, it’s not illegal, and a lot less fattening than booze.

So go ahead and make a new year’s resolution to be more cheerful, and then help ensure that you meet that resolution with a charitable investment today.

Mr. Brooks, the Louis A. Bantle Professor of Business and Government Policy at Syracuse University’s Maxwell School, is a visiting scholar at the American Enterprise Institute. He is the author of “Who Really Cares” (Basic Books, 2006).