ST. LOUIS, Feb. 9 (UPI) -- Men married to women with higher incomes were more likely to use erectile dysfunction medication than male breadwinners, U.S. and Danish researchers say.

Lamar Pierce, a professor of strategy at Washington University's Olin Business School, and co-authors Michael S. Dahl at Aalborg University in Denmark and Jimmi Nielsen at Aarhus University Hospital, said they based their research on data collected from more than 200,000 married Danish couples from 1997 to 2006.

The study, "In Sickness and in Wealth: Psychological and Sexual Costs of Income Comparison in Marriage," also found wives who out-earned their husbands were more likely to suffer from insomnia and to use anti-anxiety medication.

The researchers said they did not find these effects for unmarried couples or for men earning less than their wives prior to marriage.

The researchers' findings were published in the journal Personality and Social Psychology Bulletin.