Story last updated at 12/2/2009 - 12:14 pm
Over the past few years, medical researchers have been exploring the role of vitamin D and its relationship to a healthy body. One of the first diseases contributed to low levels of vitamin D was rickets in children. Symptoms of rickets were growth retardation and skeletal deformities. According to Dr. Michael Holick, Boston University School of Medicine, "Once foods were fortified with vitamin D and rickets appeared to have been conquered, many health care professionals thought the major health problems resulting from vitamin D deficiency had been resolved."
We now know that vitamin D deficiencies are associated with osteoporosis, muscle weakness, cancers, autoimmune diseases, cardiovascular disease, and bone pain.
Vitamin D was misnamed. It is not actually a vitamin but a hormone that transports calcium from the intestine into the bloodstream. Without it, only 10-15 percent of the calcium found in foods would be absorbed. With it, the absorption rate climbs to 30-40 percent. That is why foods, such as milk, are fortified with vitamin D. The body can manufacture vitamin D, but it needs help from the sun. In fact, sunlight is the best source of vitamin D yet the supply depends on the amount of skin surface exposed and the quality of the sunlight.
Deficiency is common in all populations above 35-degrees latitude (the horizontal line located at approximately Atlanta, Georgia). In Southeast Alaska, the quality of sunlight is not great - this is true in the summer as well as in the winter months. Therefore, a large percentage of the population is at significant risk much of the year for vitamin D deficiency.
On the VitaminDHealth.org website, it was reported that "one of the reasons influenza occurs in the winter time... is because the sun is unable to produce vitamin D, and the resulting vitamin D insufficiency may promote and enhance the infectivity of the influenza virus."
It can be surmised that people already deficient in vitamin D may be at increased risk of getting the flu. A controlled study found that a low dose of 800 IU per day reduced incidences of seasonality colds and flu. A higher dose of 2000 IU per day eliminated all reports of colds or flu.
What is the recommended daily intake (RDI) for vitamin D? The safe upper intake level is set at 2,000 IU per day. However, for many, this may be too low. Some studies have shown that adults need 3,000-5,000 IU per day. The best way to determine your RDI value is to have your blood level tested. This can be done by your medical provider or through the Alaska Health Fair (see the calendar online at www.alaskahealthfair.org).
A concern held by many people is the risk of vitamin D intoxication. My research found that intoxication is extremely rare - a fact verified by my medical provider. An extremely high dose would be more than 50,000 IU per day (a medicine at this dosage, not a supplement).
In my November article for the Capital City Weekly (November 4, 2009), I provided five doctors' tips for avoiding seasonal cold and flu. To this list, add No. 6: Have your vitamin D level checked to ensure you are receiving an adequate amount from your diet or supplements. Increased vitamin D may be the answer to a flu-free season.
Sonja Koukel, PhD, is an assistant professor in the Health, Home & Family Development Program for the Cooperative Extension Service UAF Juneau District. Reach her at firstname.lastname@example.org or 907-796-6221.