The numbers of people with seasonal affective disorder (SAD) and influenza reach their peak in February and March. This year has been particularly bad for the flu. Much of this has to do with the vaccine being somewhat less effective against this year’s strain of influenza. But, this winter has also produced a record number of freeze thaw cycles throughout the Midwest and Northeast, depleting road salt supplies and creating horrible pot holes.
How does all this cause seasonal effective disorder and the flu? We have always thought seasonal affective disorder (SAD) was due to the lack of sun exposure. The shortest day of the year is December 21st. So SAD should be at its worst just before the end of the year. But we feel lousy now, why is that?
Well it’s not the light or lack of it that is the problem. It is what the light does for us. Ultraviolet B radiation is necessary to make vitamin D. It also inactivates influenza virus. For those of us in the Midwest, we stop making vitamin D from sunlight in October and we cannot make it again until late March or April. So although the shortest day of the year is in late December, our vitamin D levels do not bottom out until March. And, in studies, it’s vitamin D replacement that relieves symptoms of SAD.
The flu season also follows this pattern because vitamin D is important for fighting infections in all animals. Additionally, recent studies show that when the humidity falls below about 35 percent the transmission of flu virus goes up dramatically. Without UVB to make vitamin D or inactivate viruses outside our bodies, there are more viruses floating around in the cold, dry air to infect vulnerable people with low vitamin D levels.
A healthy diet and exercise have also been shown to improve your defenses against infection and lower your risk of depression. The solution to all of this is to humidify the air where you live and work, wash your hands frequently, and do The Vitamin D Cure.