Why is there a "flu season"? Is it linked to a lack of humidity, temperature, exercise in the winter, or as Dr. Hope-Simpson proposed in 1981, is it associated with a decrease in solar radiation?
Scientists are researching the effect of winter's lack of sunshine to a seasonable drop in available vitamin D in humans and increased infections. Since a majority of the earth's population lives in the northern hemisphere and flu epidemic occurrences peak from December to March each year, it seems obvious there is a link to the sun. It could be thru a variance of body vitamin D production.
The sun provides the exposed skin with energy to produce thousands of units of vitamin D a day during the summer, but very little in the winter. Certain northern countries such as Norway, have lower flu levels than other countries, which may be due to its high cod liver oil consumption - which provides the body with higher amounts of dietary vitamin D.
Although vitamin D is known as a nutrient required for calcium absorption and healthy bones, it also is involved in immune function. The active form of this vitamin helps regulate macrophages (white blood cells) and increase their capacity to fight infection. Low vitamin D levels have been associated with increased rates of infectious disease and longer duration of infections.
A small study of 47 young children conducted by Dr. Linday in 2004, found that giving cod liver oil plus a multivitamin daily, helped significantly reduce the number of their respiratory problems from late autumn to early May. The cod liver oil plus multivitamin supplied 600-700 IU of vitamin D daily.
Other studies conducted in the 1930's and in 1997 showed links between large amounts of vitamin D consumption and reduced respiratory infection. Experts have also recently evaluated the relationship between influenza (flu) outbreaks and vitamin D levels, based on seasonal occurrences. Worldwide, influenza outbreaks occur more often in the winter months. And, inadequate vitamin D levels are more widespread in the winter months.
These experts stated:
¥ "Vitamin D has profound and multiple effects on human immunity."
¥ Current recommendations for vitamin D intake levels are set too low.
¥ Influenza may be a sign of vitamin D deficiency.
¥ Pharmacological doses (1,000-2,000 IU/kg per day for several days) may be useful as a
treatment for viral respiratory infections that peak in wintertime. More research is needed
to test the theory that vitamin D influences the course of viral respiratory infections.
The researchers feel there may be a vitamin D-flu linkage, but it is premature to recommend increased vitamin D supplements for respiratory infection at this time. However, they suggest vitamin D deficiency be diagnosed and treated.
Look for future larger studies researching this connection further. In the meantime, my family has already started taking more vitamin D and a little more sun.
1. Zittermann A., "Vitamin D in preventative medicine: are we ignoring the evidence?" British Journal of Nutrition, 2003;89:552-572.
2. Proudfit FT. Nutrition and Diet Therapy. A Textbook of Dietetics 7th Edition. 1938 Macmillan Company.
3. Linday L. and others, "Lemon-flavored cod liver oil and a multivitamin-mineral supplement for the secondary prevention of otitis media in young children: pilot research." Ann. Otol. Rhinol. Laryngol., 2002 Jul.;111(7 Pt 1):642-52.
4. Linday L. and others, "Effect of daily cod liver oil and a multivitamin-mineral supplement with selenium on upper respiratory tract pediatric visits by young, inner-city, Latino children: randomized pediatric sites." Ann. Otol. Rhinol. Laryngol., 2004 Nov.;113(11):891-901.
5. Cannell J. and others, "Epidemic influenza and vitamin D." Epidmiol. Infect 2006. 1-12.