For many people post-holiday blues are as common as returning gifts.

Studies show much of the population can be affected by seasonal mood changes and it's not limited to the poor or lonely.

Seasonal Affective Disorders -- known as SAD -- have symptoms similar to depression and can include a lack of energy, an increased need for sleep, and a craving for foods that put on the pounds.

Latitude plays a role in the problem. SAD almost doesn't exist in Florida but is quite high in Alaska.

"The closer you are to the equator, the better your mental health," said Karen Lieberman, with the Mood Disorders Association of Ontario.

"With SAD you have depression, changes in appetite, weight gain and you can sleep the sleep of the dead and feel like you can't get enough."

The most common treatment for SAD is the use of light therapy to the patient's eye which is effective in 60% of patients.

Symptoms begin in the fall and peak in the winter and clear up by the spring.

Sufferers of SAD should try to get outdoors and have moderate exercise.

"It is also a time to eat foods like fish and almonds," Lieberman said.

Although the suicide rate doesn't rise at Christmas, the health-care system will see more psychiatric patients over the holiday season than at any other time of year.

Experts agree that to avoid holiday blues, regular sleep and eating patterns should be maintained, holiday expectations should be kept reasonable to avoid letdowns, and activities should be planned for after Christmas.