Could the remarkable association between influenza epidemics and the winter season be explained by the well known deficiency of vitamin D that occurs when the sun dips so low in the sky that humans can no longer make vitamin D in the skin? I think so, and science is just starting to unravel this connection.
British physician Robert Edgar Hope-Simpson was the first to propose a connection between influenza epidemics and the season. He documented the fact that influenza outbreaks all around the world peak just after the winter solstice, are worse at higher latitudes, and less severe at the equator except for the rainy season when people were indoors. He theorized a “seasonal stimulus” related to the direct solar radiation in the summer months that protected us against influenza.
The influenza virus is present year round and can be found in about 2% of humans at any given time. Why is it, then, that influenza related illness occurs suddenly in about 15% of the population right around the winter solstice and virtually disappear during the summer months? There is mounting evidence that vitamin D deficiency might be the underlying reason.
Vitamin D is made in the skin upon exposure to UVB rays in direct sunlight. Multiple aspects about vitamin D support it being the “seasonal stimulus” that Dr Hope-Simpson’s theory proposed:
- Vitamin D has profound and multiple effects on human immunity
- Serum levels of vitamin D are low in many people who live in temperate latitudes, especially in the winter
- Inadequate vitamin D nutrition is common in the elderly who also only make about 25% of the vitamin D as 20-year-olds after exposure to the same amount of sunlight
- Routine supplementation with only 400 IU of vitamin D does not prevent the deficiencies observed in wintertime
Research in the last decade has shown that vitamin D helps our immune system fight microbes by increasing the activity and killing power of certain white blood cells, as well as increasing the amount of internally generated antibodies that fight microbes, including viruses such as influenza.
Vitamin D and Respiratory Illnesses
People in Norway have very little seasonal variation in vitamin D levels due to high intake of vitamin D in fish and cod liver oil, while people in Britain have marked vitamin D deficiency in the winter. Excess wintertime mortality is twice as high in Great Britain as in Norway.
Melanin pigment in the skin limits the ability to make vitamin D. African-American adults have much lower vitamin D levels than Caucasians and their mortality from influenza is much higher, while African-American children have twice the pneumonia mortality of white children.
Similar correlations lead me to suspect that vitamin D may be responsible for many things, including why:
- Children exposed to sunlight are less likely to get colds
- Cod liver oil intake reduces the likelihood of getting viral infections
- Using UVB lamps in factories and schools leads to reduced colds and flu
- Children given high doses of vitamin D have less infections
What to do to prevent the flu?
Avoid transmission of the flu by using alcohol based hand sanitizers, cover the cough, and if possible stay home from work or public gatherings during the peak flu season. And, perhaps most important, get your vitamin D level checked!
During the winter months, from the fall to spring equinoxes, my children get 2000 IU of vitamin D3 daily while I increase my usual 3500 IU daily up to 5,000 IU. Normal blood levels of vitamin D are 30-80 (ng/ml), with 10 the minimum to prevent rickets, 34 the minimum to absorb calcium, and up to 50 associated with greater neuro-muscular strength.
While the pharmacologic potential and exact mechanisms of vitamin D are just beginning to be explored, from what I can determine is makes sense to keep your winter-time vitamin D level above 50 ng/ml, which is consistent with a natural summer-time level.
There are instances in medicine when a certain disease is found primarily in correlation with another underlying disease. For example, Pneumocystis pneumonia and a rare cancer called Kaposi’s sarcoma, occur so exclusively in AIDS patients they are considered “AIDS defining illnesses”. Perhaps a similar analogy can be made between influenza and vitamin D deficiency, such that some day influenza may be considered a “Vitamin D deficiency defining illness”.
Scott Rollins, MD, is Board Certified with the American Board of Family Practice and the American Board of Anti-Aging and Regenerative Medicine. He specializes in bioidentical hormone replacement for men and women, thyroid and adrenal disorders, fibromyalgia and other complex medical conditions. He is founder and medical director of the Integrative Medicine Center of Western Colorado (www.imcwc.com) and Bellezza Laser Aesthetics (www.bellezzalaser.com). Call (970) 245-6911 for an appointment or more information.