* Nike down after flagging weakness in N. America sales
* Celgene falls after follicular lymphoma regimen fails trial
* Indexes down: S&P 0.07 pct, Nasdaq 0.11 pct, Dow 0.09 pct (Changes comment, updates prices, adds details)
By Sruthi Shankar
Dec 22 (Reuters) - The blue-chip Dow Jones index was lower in thin pre-holiday trading on Friday, pressured by losses in UnitedHealth and Nike.
Shares of UnitedHealth were down 1.2 percent after the health insurer agreed to buy Chilean healthcare company Banmedica SA for $2.8 billion.
Nike forecast muted current-quarter revenue growth that took a toll on its shares, which fell 3.1 percent.
"Volumes in the stock market are down 28 percent," said Michael Antonelli, managing director, institutional sales trading at Robert W. Baird in Milwaukee.
U.S. markets are shut for the Christmas holiday on Monday.
Still, major Wall Street indexes were on track to end the week higher, buoyed by a historic overhaul of the U.S. tax code.
President Donald Trump signed Republicans' massive $1.5 trillion tax overhaul into law on Friday and also approved a short-term spending bill that averts a possible government shutdown.
At 10:57 a.m. ET (1557 GMT), the Dow Jones Industrial Average was down 22.45 points, or 0.09 percent, at 24,759.84 and the S&P 500 was down 2 points, or 0.07 percent, at 2,682.57.
The Nasdaq Composite was down 7.99 points, or 0.11 percent, at 6,957.37.
Data on Friday showed U.S. consumer spending accelerated in November and shipments of key capital goods orders increased for the 10th straight month, the latest signs of strong momentum in the economy as the year winds down.
"The data is relatively mixed but biased to the upside, and consumer sentiment continues to be strong and that bodes well for economic strength in 2018," said Matthew Miskin, market strategist at John Hancock Investments in Boston, Massachusetts.
Wildly volatile bitcoin plunged below $13,000, losing around a third of its market value in five days. Companies that have been trying to ride the bitcoin wave were hit hard by the cryptocurrency's slump.
Long Blockchain, Overstock.com, Xunlei , Riot Blockchain and Marathon Patent Group tumbled between 6 percent and 17 percent.
Six of the 11 major S&P sectors were higher, led by a 0.41 percent gain in utilities. Financial stocks fell 0.47 percent and were the biggest losers.
Celgene shares fell 1.4 percent after the company's follicular lymphoma regimen failed in a clinical trial.
Ignyta soared about 72 percent after Swiss drugmaker Roche said it would buy the U.S. cancer drug specialist for $1.7 billion.
Declining issues outnumbered advancers on the NYSE by 1,386 to 1,345. On the Nasdaq, 1,572 issues fell and 1,138 advanced. (Reporting by Sruthi Shankar in Bengaluru; Editing by Anil D'Silva)