The stock market’s reliance on a handful of companies to drive gains is a perilous warning sign that investors should heed, says investment strategist Michael E. Lewitt.

iPhone maker Apple Inc. is leading the “Four Horsemen of the Apocalypse” of stocks that are vital to the equity market’s health, he says in this month’s edition of his Credit Strategist newsletter. The other three companies are Google Inc., Amazon.com Inc. and Facebook Inc.

“If these stocks ever stop rising, there is going to be one hell of an apocalypse in stocks,” Lewitt says. “Under the headlines, the market has started to look decidedly unhealthy.”

The S&P 500 index of the biggest U.S.-listed companies has advanced less than 1 percent this year with energy, commodity-related and industrial materials companies under pressure. Biotechnology, healthcare, technology and consumer discretionary stocks have done most of the heavy lifting.

Lewitt says it’s worrisome that $1.7 trillion of market value can be attributed to the “Four Horsemen,” especially at their earnings multiples. The S&P 500 has a total market capitalization of about $7.8 trillion.

“If the Four Horsemen need some charioteers to steer them, they can call on Gilead Sciences and NetFlix, since these six stocks collectively have accounted for more than 50 percent of the $664 billion in value added to the Nasdaq Composite Index so far this year,” he says. “If we substitute Walt Disney Co. for NetFlix, this line-up of six stocks has accounted for more than 100 percent of the $199 billion rise in the market value of the S&P 500 in 2015.”

Apple traded at a price-to-earnings ratio including cash of 14.4 times, Google 28 times and Facebook 94 times, while Amazon.com was off the charts, according to Lewitt's calculations.

The market’s dependence on a handful of companies for gains doesn’t necessarily mean stocks will stop advancing, he says.

“In recent weeks, breadth has been declining although it should be pointed out that we saw breadth narrow more significantly on the New York Stock Exchange in each of the last four years and the market kept rising,” he says.

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