With the TSX plunging more than 500 points on Monday morning, more than a few Canadians might give credence to a British psychologist's pseudo-scientific formula that indicates Jan. 21 will be the most depressing day of 2008.

Cliff Arnall began calculating the happiest and gloomiest days of the year back in 2005 while working as a professor at Cardiff University in Wales.

At the behest of the British travel industry, Arnall devised a "Blue Monday" formula that calculates factors such as weather, debt, time passed since Christmas, failed New Year's resolutions, low motivation and the need to take action.

While there is no scientific support for Arnall's theory — some might find the formula 1/8W+(D-d)3/8xTQMxNA itself too depressing even to contemplate — anyone suffering from the winter blues or just a bad case of the Mondays can take comfort in the fact that they aren't alone.

Health Canada estimates two to three per cent of Canadians suffer from seasonal affective disorder (SAD) and another 15 per cent of Canadians suffer from a milder version simply known as the winter blues. 

These seasonal conditions can affect moods, sleep patterns, appetites, energy levels and concentration. Exercise, experts say, is the best way to keep seasonal depression at bay.

Here are a few tips from Health Canada:

• If you are already active, try to maintain or increase your level of physical activity.
• Exercise outdoors during daylight hours.
• If indoors, exercise by a window.
• Build activity into your lifestyle, for example, by taking the stairs or public transit and walking part of the way to work.