The secret ingredient to a happy marriage is not only communication, openness, and moral support, but also a code that can solidify and fortify a relationship for years to come, according to a recent study. The findings suggest that the length of the “happy hormone” gene variant, 5-HTTLPR, may predict a couple’s chances of achieving life-long marital bliss.

Researchers from the University of California Berkeley and Northwestern University sought to investigate if the length of the “happy hormone” gene determined wedded bliss in 156 couples, middle-aged and older, who were followed since 1989 for more than 20 years.

The researchers examined the gene, 5-HTTLPR, which regulates serotonin. The “happy hormone” has the ability to stabilize moods, prevent depression, and make a person feel happy. There are two variants of 5-HTTLPR genes — long and short — that are inherited from a person’s parents. In the study, these genes were used as a predictor of how much a person’s emotions affect his or her relationships.

The participants provided DNA samples that were used to match their genotypes with their levels of martial satisfaction and the emotional level of their interactions. Facial expressions, body language, and discussion topics among spouses were analyzed in the researchers’ lab.

Seventeen percent of the spouses were found to have two short 5-HTTLPR alleles. The researchers noted a strong correlation between the emotional tone of conversations and how the couples felt about marriage. The participants with two short variants of 5-HTTLPR were most unhappy in their marriages when there was a lot of negative emotion, such as anger and contempt. However, these couples with the short variants of the gene were most happy when there was positive emotion, such as humor and affection.

“Individuals with two short alleles of the gene variant may be like hothouse flowers, blossoming in a marriage when the emotional climate is good and withering when it is bad,” said lead author of the study, Claudia M. Haase of Northwestern University, the Daily Mail reports.

“Conversely, people with one or two long alleles are less sensitive to the emotional climate."

Eighty-three percent of the couples were found to possess either one or two long variants of 5-HTTLPR. Researchers did not find a significant correlation between the emotional quality of discussion and marital status in spouses who had one or two long alleles. These participants were less bothered by the emotional ups and downs of their marriages.

While couples that possess two long genes may have better emotional stability, couples with two short variants should not panic about whether their marriage is built to last.

"Neither of these genetic variants is inherently good or bad. Each has its advantages and disadvantages,” said Haase.

According to the Centers for Disease Control and Prevention, there are approximately 2.1 million marriages in the United States with half of these couples filing for divorce.