It's time for another Blue Monday, supposedly determined by a scientific formula to be the most depressing day of the year. This dismal day is generally said to fall on the third Monday of January, which would mean Blue Monday 2012 is Jan. 16.

The formula incorporates several factors related to depression, including weather, debt, lack of motivation and time elapsed since Christmas. It was created for a marketing campaign in 2005 on behalf of Sky Travel, which reportedly wanted to promote January vacations as a way of beating the blues.

According to British psychiatrist Ben Goldacre, who writes the Guardian's "Bad Science" column, the public relations firm Porter Novelli shopped the idea of Blue Monday around to various scholars in search of an academic endorser. It finally found one in Cliff Arnall, a psychologist and "life coach" who formerly worked at Cardiff University's Centre for Lifelong Learning in Wales.

As outlined in an email Arnall sent to MNN this week — as well as a press release by the nonprofit Flexible Thinking Forum — the Blue Monday formula looks like this:

The letters above represent: weather (W), debt (D), time until next payday (d), time since Christmas (T), time since failing New Year's resolutions (Q), low motivation (M) and the feeling of a need to take action (Na). The press release doesn't explain how to assign values for all these variables, but Arnall tells MNN the formula "isn't designed for numerical inputs," adding that "You can assign rankings to each of the factors, but the formula really serves as a way of improving and understanding why lots of people feel down at this time."

Of course, it's hardly groundbreaking to suggest January is a sad time for many people. Dreary weather triggers seasonal affective disorder in up to 6 percent of Americans, while other wintry tendencies like vitamin D deficiency and lack of exercise may also spur depression. But as Goldacre wrote in 2006, "Cliff Arnall's equations are stupid, and some fail even to make mathematical sense on their own terms." Such fanciful formulas, he added, "serve only to caricature and undermine science."

Whether or not that's true, Arnall's equations have at least failed to clarify when we should observe Blue Monday. Due to the formula's fuzziness, some people (including Arnall) say it's the third Monday in January, while others insist it falls on the month's last full week — meaning Blue Monday 2012 would be Jan. 23, not Jan. 16.

Still, despite its negativity and ambiguity, Blue Monday may have a silver lining. Sky Travel closed in June 2010, leaving the concept floating around freely in the public sphere. And now, rather than coaxing consumers into hasty vacations, Blue Monday has evolved into a sort of public-awareness day for depression and malaise.

The nonprofit, organized by England's Canterbury College, offers this vision: "Blue Monday isn't about raising money ... It's about doing good for others, whether it's for one person or something global." And — which is run by the Flexible Thinking Forum as well as PR firm Green Communications — promotes Blue Monday as a time "to raise both a smile among the British public and valuable funds for the mental health charities."

(Arnall tells MNN he now likes to call it "Red Monday," to reflect how a weak economy can increase depression, although that term doesn't seem to have caught on yet.)

About a quarter of the U.K. population suffers from some kind of mental health problem over the course of a year, mainly depression and anxiety, according to the nonprofit Mental Health Foundation. In the U.S., roughly 8 percent of all adults are affected by "major depression" in a year. And the World Health Organization estimates that 121 million people worldwide are clinically depressed, yet fewer than 25 percent of them receive any kind of formal treatment.

Blue Monday thus casts an important spotlight on real mental health problems. But that doesn't mean it has abandoned its roots as a corporate marketing tool.

On Jan. 23, for example, Tropicana will unveil a 72-foot sun in London's Trafalgar Square, hoping to link Blue Monday with the juice company's "Brighter Mornings" campaign. And Ambius, an office-environment consulting firm, is using the day to highlight connections between "workplace malaise" and lost productivity, suggesting companies use office plants to boost morale. "Let's hope Blue Monday provides the impetus for businesses to go green in 2012," an Ambius executive tells HR Magazine.

For more ideas about natural depression remedies — whether it's Jan. 16, Jan. 23 or any other day of the year — check out these articles from MNN:

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Blue Monday strikes again
The 'most depressing day of the year' may be on shaky scientific ground, but it does provide a rare spotlight for easily ignored mental health issues.