Dark days are ahead. Consider your intake of vitamin D.
The most important source of vitamin D is sunlight, but north of the 42 degree north latitude line, you might need supplemental vitamin D. Where does that come from? Food, especially mackerel, mushrooms, and margarine.
David McCandless put together this graphic that provides a good overview of the subject, coming as the shortest days of the year approach. Click on the image below for his sources.