A reader asks:

Why am I so tired in the morning during the winter months?


Our internal biological clock–which strongly influences our daily patterns of alertness and energy, sleep and waking–is very sensitive to early morning illumination. Since the sun rises later in winter (in the northern hemisphere above the equator), the biological clock is vulnerable to drifting later, leaving us tired in the morning. The essence of morning light therapy is to correct that drift, thereby restoring normal morning energy and alertness.