* Amazon jumps to record high after posting unexpected profit
* Biogen's fall weighs on Nasdaq, S&P
* Hillary Clinton to propose raising capital gains tax - report
* Visa, Starbucks rise after results
* Indexes down: Dow 0.57 pct, S&P 0.56 pct, Nasdaq 0.32 pct (Updates to early afternoon)
By Tanya Agrawal
July 24 (Reuters) - Wall Street was lower in early afternoon trading on Friday for the fourth straight day as a fall in materials and health stocks and a fall in commodities overshadowed strong results from Amazon, Visa and Starbucks.
Amazon.com shares jumped as much as 20.4 percent to a record of $580.57 after the online retailer posted an unexpected quarterly profit. The jump catapulted Amazon's market value to about $270 billion, overtaking Wal-Mart.
Metal prices hit multi-year lows as weaker-than-expected data from China and the euro zone raised concerns about global growth while oil prices neared four-month lows.
The three major indexes were poised to end the week in the red as Biogen's 19 percent slump weighed the most on the Nasdaq and the S&P 500 and dragged down other health stocks.
Adding to the day's pressure, Democratic presidential candidate Hillary Clinton will propose nearly doubling the U.S. capital gains tax rate on short-term investments, the Wall Street Journal reported.
Second-quarter S&P 500 earnings have been mixed, with 74 percent of companies beating analysts' profit expectations but just 52 percent surpassing revenue expectations, according to Thomson Reuters data.
RBC Capital Markets said investors were treating disappointing stocks harshly. While only 20 percent of companies have missed expectations, below the 23 percent over the past three years, there was a 3.5 percent selloff versus the 2.4 percent seen historically, a note said.
Adding to the concerns regarding lukewarm earnings, the S&P 500 is relatively expensive, trading at 16.9 times forward 12 months' earnings, above the 10-year median of 14.7 times, according to StarMine data.
"We are not going to see a lot of earnings growth in the second half of the year as the economic data hasn't been very strong," said Paul Nolte, portfolio manager at Kingsview Asset Management in Chicago.
"The fall in commodities is also a concern that global growth is slowing and that ties into U.S. growth too."
Data on Friday showed new U.S. single-family home sales fell in June to their lowest level in seven months and May's sales were revised sharply lower. Other data showed manufacturing activity nudged up in July after slowing for three straight months.
At 12:43 p.m. ET (1643 GMT), the Dow Jones industrial average was down 100.26 points, or 0.57 percent, at 17,631.66, the S&P 500 was down 11.81 points, or 0.56 percent, at 2,090.34 and the Nasdaq Composite was down 16.61 points, or 0.32 percent, at 5,129.80.
Six of the 10 major S&P 500 indexes were lower with the materials index's 1.79 percent fall leading the decliners.
Dow component Visa was up 4.3 percent at $74.87 after the credit and debit card company's results handsomely beat expectations.
Starbucks rose 2.4 percent to $57.96 after the world's biggest coffee chain reported a higher quarterly profit.
Stancorp Financial Group soared 48.1 percent to $113.59 after Japan's Meiji Yasuda Life Insurance said it has agreed to buy the company for $5 billion.
Truecar slumped 34.9 percent to $6.98 after the online car-shopping service provider cut full-year revenue forecast.
Declining issues outnumbered advancers on the NYSE by 2,046 to 911. On the Nasdaq, 1,815 issues fell and 870 advanced.
The S&P 500 index showed 12 new 52-week highs and 51 new lows, while the Nasdaq recorded 44 new highs and 141 new lows. (Editing by Don Sebastian)