Seasonal Affective Disorder (SAD) symptoms usually begin to appear in November — a month known for its clouds, its icy lakes, the lowering angle of sunlight, and its shorter days.

It's the shortage of daylight that affects as many as one in three Minnesotans during the winter months, causing anxiety and depression. Other symptoms include a craving for carbohydrates and an urge to sleep more.

Some researchers speculate that SAD may be a throwback to thousands of years ago when our ancestors sort of "hibernated" during the cold winter months, living off food they had stored up and sleeping through cold spells.

A lack of sunlight, especially during December and January, seems to affect the production of the hormone melatonin, leaving some people with a weak or rundown feeling. Minnesotans with the means often choose to winter in sunnier and warmer locations such as Florida, Arizona and Southern California. Others are helped by using better lighting in their homes and workplaces. For example, full-spectrum fluorescent lights mimic the sun, giving off light in a wide range of frequencies. These lights may help many people get out of their winter funk, but if anxiety and depression are involved, it's important to consult your physician before using light or another kinds of therapy.

Fortunately, many Minnesotans really enjoy winter. Ice skating, ice hockey, sledding, snowshoeing, skiing, ice fishing, walking nature trails and feeding wildlife are just a few activities that can keep you happy in winter.

Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays.