As the U.S. slump spreads from the domestic housing market to consumer spending, the global economy could begin to see the effects, Bloomberg News reported.

In the past 18 months, a U.S. economic slowdown has not prevented the world economy from growing at an annual rate of more than 5 percent. However if U.S. economic growth falls below an annual rate of 2 percent from an average of 2.3 percent in the first half of the year, global economic growth could slow to about 4.75 percent, according to forecasters at Morgan Stanley & Co., Global Insight and the Economist Intelligence Unit. A U.S. recession could cut global growth to 3.5 percent or less.

Already global investors and lenders have become more cautious. Spanish housing starts dropped 21 percent in May and Irish house prices had their first annual decline in at least a decade in July. Merrill Lynch & Co.’s Mortgages plc unit in the United Kingdom and Deutsche Bank AG have tightened terms on their home loans, raising the cost for borrowers with less-than-perfect credit ratings. Central bankers in England, Europe, Canada, Australia and South Korea chose not to raise interest rates last week.

Asia, which relies heavily on exports, could be especially vulnerable as U.S. consumer spending rose at an annual rate of 1.4 percent in the second quarter, the slowest pace in a year. Export growth in Thailand slowed to an annual rate of around 6 percent in July and August from 18.1 percent in June. The United States accounted for about one-fifth of China’s record $107.7 billion exports in July.