Currency havens are disappearing as Switzerland and Japan intervene in foreign-exchange markets, while U.S. and European debt loads undermine credit ratings.

The biggest beneficiaries in the $4 trillion-a-day currency market may be Norway's krone and the Australia and New Zealand dollars, according to Frankfurt Trust, which oversees about $23 billion. All have debt that is less than 48 percent of gross domestic product, compared with about 60 percent in the U.S., 77 percent in the U.K. and 79 percent in Germany, according to data compiled by Bloomberg.

The Swiss franc and Japanese yen, which had become favorites of traders skittish about holding dollars and euros, became perilous after the Swiss National Bank unexpectedly cut interest rates and Japan sold its currency. The yen weakened as much as 3.2 percent on Aug. 4, according to Bloomberg Correlation-Weighted Indexes. The U.S. came within days of defaulting and Italian and Spanish bond yields approached levels that spurred bailouts of Greece and Ireland.