US stocks closed slightly lower on Wednesday 22 June, as investors count down the hours before the all-important referendum that will determine whether the UK will remain or leave the European Union. Polls ahead of the 23 June vote reveal it is still too close to call.

According to MarketWatch, a recent online survey by Opinium revealed the leave camp has 45% support, while the remain camp follows closely behind with 44%. Another 9% of voters were undecided. Results of the EU referendum are not expected until after the US market close on 23 June.

The Dow Jones Industrial Average dropped 48.90 points, or 0.3%, to settle at 17,780.83. McDonald's, which fell more than 1.5%, was the biggest contributor to declines and was downgraded to "neutral" from "buy" on expectations of weaker sales, CNBC reported.

The S&P 500 fell 3.45, or 0.2%, to close at 2,085.45, with energy weighing heavily and healthcare contributing the most to gains. Meanwhile, the Nasdaq Composite Index shed 10.44 points, or 0.2%, to end at 4,833.32. The iShares Nasdaq Biotechnology ETF (IBB) rallied following earlier losses and closed around two-thirds of a percent higher.

US crude oil futures for August 2016 delivery dropped $0.72 (£0.49;€0.64), or 1.44%, to $49.13 (£33.16;€43.34) a barrel. According to CNBC, WTI came off session highs to briefly trade over 2.5% lower following a EIA report stating crude oil stocks declined to a smaller-than-expected 917,000 barrels.

Overseas, European markets settled higher, while Asian stocks closed mixed. The German DAX closed about half a percent higher. In Asia, the Nikkei 225 was down 0.6% but the Shanghai Composite closed up around 0.9%.

The US dollar index traded about 0.25% lower, with the euro by $1.129 and the yen around 104.4 yen against the greenback. The sterling struggled against the dollar and was last near $1.470, according to reports by CNBC.

Treasury yields traded lower, with the 10-year yield near 1.68% and the 2-year yield near 0.75%. Gold futures for August delivery dropped $2.50 (£1.69;€2.21) at $1,270 (£857.27;€1,120.62) an ounce.