The urge to merge. The search for a soul mate. Be it hearts and minds, bodies or souls, the desire of humans to connect with each other may be the most basic of instincts, the mating ritual, mankind's most primal.
But while anthropologists have long known that the complex combination of biological and evolutionary factors that drive humans to couple and reproduce ensures the well-being of the species, decades of research into human sexuality, brain chemistry, mental health, longevity —even the nutritional value of wine and chocolate — have increasingly shown that the health of a person's love life has a direct impact on his or her mental and physical health.
"Love and intimacy are the root of what makes us sick and what makes us well, what causes sadness and what brings happiness, what makes us suffer and what leads to healing," Dean Ornish, M.D., writes in his book, "Love & Survival: the Scientific Basis for the Healing Power of Intimacy." "Our survival depends on the healing power of love, intimacy, and relationships."
Last year, the Centers for Disease Control (search) even put its stamp of approval on coupledom, reporting in December that married people were healthier than those who were single, divorced, widowed or separated.
Love and the Brain
Your heart races, your palms sweat. Lovers often talk about the "chemistry" they feel with the object of their affection, but few know just how scientific that chemistry is. The physical responses that come with feelings of love and attraction are actually the effects of brain chemicals, known as neurotransmitters (search), triggering different reactions.
On fire with lust? Blame eruptions of testosterone. Can't get your beloved out of your head? That's because your brain is swimming in a biochemical cocktail of serotonin, dopamine and norepinephrine (search) — similar to the chemical combination found in the brains of patients with obsessive-compulsive disorder (search).
People who report feeling "intoxicated" by another person know of what they speak. Dopamine is the brain's pleasure chemical, activated by alcohol and drug use. When love triggers its release, it provides a natural high.
Even that comfy and content feeling that comes with long-term love has a chemical source. Oxytocin (search), sometimes called the "cuddling hormone" because it is released by touch, is at work in this phase of a relationship, and is also responsible for child-parent bonding.
The Marriage Benefit
According to the CDC report, married people were half as likely to be smokers than non-marrieds, were less likely to drink alcohol, were more physically active than non-marrieds, and were also less likely to suffer from headaches, back pain and psychological stress disorders.
"Married persons were healthier for nearly every measure of health," says the CDC.
Of course, researchers don't really know why marrieds are healthier. For example, it could be that marriage attracts healthy people. Additionally, studies have found significant disparities between the health benefit of marriage between women and men. While nearly a century of research has trumpeted the good health of married men, research has found that women only reap that benefit if the relationship is good. Married men, on the other hand, were healthier regardless of the quality of the relationship.
A 2003 study by Linda C. Gallo, Ph.D., found that while happily married women were thinner, exercised more, aged better, and were less likely to get heart disease than singles, women in unhappy marriages were at the highest risk for poor health.
But you don't have to be married to reap the health perks or problems of love.
"It doesn't necessarily have to be heterosexual cohabitation," Gallo told WebMD Medical News. "Human connectedness is a basic fundamental need for people. Marriage or being in a close relationship is an important part of life. When it is good, it doesn't just make life pleasurable. It is good for health. When people are in happy situations, maybe they exercise together; maybe they sit down to healthy meals together. It is adaptive."
Let's Talk About Sex
According to a 1997 study published in the British Medical Journal, men who reported at least two orgasms a week at the time of the study had less than half the risk of dying from various causes over 10 years of follow-up than those with less frequency of orgasm.
A 2001 study found that men who had sex three or more times a week reduced their risk of heart attack or stroke by half.
While that study did not take into consideration other lifestyle factors, such as diet and exercise, that may have contributed to the subjects' health, the findings seem to be backed up by earlier research. A 30-year study at Duke University, reported in the 1982 journal Gerontologist, found that the frequency of sexual intercourse, for men, and the enjoyment of sex, for women, predicted longevity.
Other studies have shown correlations between sexual dissatisfaction and heart disease. A 1976 study of women with cardiovascular disease found that 65 percent of the coronary patients reported sexual frigidity and dissatisfaction, while only 24 percent of the control subjects without heart disease reported sex problems.
From a fitness perspective, sex provides a modest cardiovascular workout, elevating pulse rates. An energetic session can burn about 200 calories, the same as a 15-minute jog. Additionally, sex prompts the body to release the hormone oxytocin and endorphins, natural painkillers that can ease all sorts of aches and pains. In women, sex causes the release of estrogen, which can ease PMS symptoms.
However, sex offers health benefits only if it is practiced safely. The ramifications of sexually transmitted diseases are overwhelmingly more dangerous than any physical benefit of sex. From HIV and AIDS to the human papilloma virus (search) that has been linked strongly with cervical cancer, sexually transmitted diseases can have devastating, even deadly, impact on health.
The Brokenhearted Brain
Everyone who has been through a bad breakup knows the heartache love gone bad can cause. But new research suggests that the grief experienced when a relationship ends badly can trigger changes in women's brains significant enough to be detected on an MRI. The study, conducted by Dr. Arif Najib (search) with the University of Tubingen Medical Center in Tubingen, Germany, found that the brains of women grieving over lost romance showed much less activity in the amygdala (search) — the region of the brain associated with emotion, motivation and attention. People experiencing post-traumatic stress disorder (search) also show lower amygdala activity.
In the case of "puppy love," the bite can be worse than the bark. According to a 2000 study conducted by Cornell University sociologist Kara Joyner, teenagers in love are more likely to be depressed, and more prone to alcohol and drug abuse, and delinquent behavior, than kids who have yet to be stung by the love bug.
Finally, for those heading out for a romantic dinner this Valentine's Day, feel free to indulge. It turns out that the flavors of love are good for you. Dark chocolate (but not milk chocolate) lowers high blood pressure and is a potent antioxidant, while studies have found that red wine reduces high blood pressure, lowers heart disease, counteracts the effects of cigarette smoking and protects against lung and prostate cancers.
Web MD reporters Jeanie Lerche Davis, Jeffrey Blum, Laurie Barclay and Denise Mann contributed to this report.