The day-to-day volatility for the S&P 500 settled down on Monday and Tuesday. But two-thirds of stocks in the U.S. large-cap benchmark index have declined this year, with 220 of the 500 stocks down at least 10% and 82 down at least 20%.

UnitedHealth Group lost more than a fifth of its value and fell 22.4 percent following a weaker-than-expected profit report.

The ripple effects of Donald Trump's global trade war are increasingly being felt across numerous industries all at once and on Wednesday were once again exerting pressure on U.S. stock markets that have been roiled for weeks by his erratic trade policies.

U.S. stocks fell Wednesday after Nvidia warned new restrictions on exports to China will chisel billions of dollars off its results, while companies around the world said President Donald Trump’s trade war is clouding forecasts for how they and the economy will do this year.