Should you give up short selling for Lent?

Leslie Shaffer | Writer for
New investment theory to consider: Buy at Lent

Investors tired of the "sell in May" market cliché might want to consider replacing it with "buy at Lent," with stocks typically posting gains over the around 40-day period.

"Over the last 70 years or so, since World War II, we've seen about an average 2 percent gain and markets up 70 percent of the time between Ash Wednesday and Easter," said George Pearkes, an analyst at Bespoke Investment Group.

(Read more: 'Sell in May,' History Says: Pro)

"It's been especially true in the last 25 years. In the last five years, it's happened five times in a row. We see this as a pretty strong trend in seasonality," he told CNBC, although he added he didn't have an explanation.

The gains were particularly striking in 2009, when the S&P 500 ran up around 10.8 percent over the period, and in 2010, there was a 7.6 percent gain.

Andreas Rentz | Getty Images

Lent is meant to be a penitential observance. Over the period, members of some Christian denominations are expected to give up something pleasurable, with choices including everything from chocolate to Facebook. In addition, observance includes abstaining from eating meat and a partial fast.

But will the brutal winter weather this year scramble the pattern?

(Read more: Pope Francis attacks 'tyranny' of unfettered capitalism)

"We've sort of seen the worst of the weather," Pearkes said. "The weather story is more going to be about impact on trailing data releases than on current stock prices."

It isn't clear how seriously investors should take the pattern when deciding whether to give up short-selling over the holiday.

(Read more: US investors biggest scaredy-cats in the world)

"If you look far enough, there's always some pattern somewhere," said Song Seng Wun, head of research at CIMB in Singapore.

But he noted, "You go into a holiday period, you're more upbeat and the expectations can carry through." In colder Northern climes, the Lent period is essentially a lead up to the end of winter and the beginning of spring.

(Read more: Why 'buy and hold' isn't all it's cracked up to be)

But Song noted the usual market suspects, including crises and macro worries, can affect typical trading patterns.

"The environment in which people operate in just before a holiday is very important," Song said. "All of these play on people's minds."

Of course, making trading decisions based on seasonal factors doesn't always pay off. In 2013, selling in May and coming back after Halloween would have been a costly move. The S&P 500 gained nearly 14 percent over the period.

—By CNBC.Com's Leslie Shaffer; Follow her on Twitter @LeslieShaffer1