The number of married couples in the United States is at a record low, according to the latest figures from the Pew Research Center.

Numbers released Wednesday show 51 percent of American adults are married, a 5 percent drop from the previous year. The median age that people get married has risen to 26.5 years for brides and 28.7 for grooms.

The numbers reflect an increase in other living arrangements that have taken hold for American adults, such as cohabitation, divorce, single parenting and the rise of grandfamilies.

If current trends continue, in just a few years there will be more single Americans than married.

In 1960, nearly 60 percent of young adults age 18 to 29 were married. Today, 20 percent have tied the knot.

Experts say America has undergone a cultural shift when it comes to getting hitched.

"In the 1950s, if you weren't married, people thought you were mentally ill," Andrew J. Cherlin, a Johns Hopkins University sociologist, told the Washington Post. "Marriage was mandatory. Now it's culturally optional."

Natasha Medina, a single woman in Los Angeles and founder of Medina Muze Management, a firm that represents production artists, said the traditional relationship between men and women has changed in the past 50 years.

Women have taken control of their careers and life, she said, "while at the same time men have asked their women to be superwomen," she said. "We've been asked to be business-oriented, a mother, a cook, a great wife ... something's got to give."

Marriage's eroding "market share" is evident not just in the United States, but all advanced post-industrial societies, the study said, regardless of economic factors.

Along racial lines, the statistics varied greatly: In 1960, 74 percent of whites were wed. Today 55 percent are married. Among blacks 31 percent are married; in 1960, 61 percent reported being hitched. For Hispanics, 48 percent are married today, compared with 72 percent in 1960.