The S&P 500 was down 0.4% to 2,061.01 in midday trading.
The Dow Jones Industrial Average was down 0.5% to 17,782.58, and the Nasdaq was flat at 4,786.68.
The yield on a 10-year Treasury bond fell 0.4% to 1.98%.
The price of gold fell 0.8% to $1,221.40.
Irvine-based ChromaDex Corp. was up 9% to $1.33 and a $150 million market cap. The natural products ingredients maker said a recently ended human clinical study involving its Niagen product showed that one dose produced “statistically significant increases” in subjects’ energy metabolism. Shares are up 30% this week.
Lake Forest-based Quantum Fuel Systems Technologies Worldwide Inc. was down 4.6% to $3.31 and a $77 million market cap on profit-taking after a big jump Monday on positive quarterly guidance. The natural gas fuel systems maker’s shares jumped by one-third Monday but are down about 15% in the past two days. It also said it would increase a line of credit with Bridge Bank N.A. from $5 million to $7.5 million.