With the unofficial departure of summer this month, establishing good exercise habits is helpful in maintaining a positive mood during the wintertime. The lack of sunlight indeed has an effect on mood and energy: direct sunlight stimulates the production of the compound cholecalciferol, which is converted into active vitamin D in the body. Vitamin D helps improve mood through a variety of mechanisms. Some studies indicate that vitamin D supplementation or extra exposure to certain types of light during the winter months help to improve mood, but the results are not conclusive. On the other hand, regular exercise is proven to improve mood, so my suggestion is to shoot for thirty minutes of vigorous activity three times per week during even the dreariest winter days. Remember, you don’t have to smile only when it’s sunny outside!