VITAMIN D – HOW TO AVOID COLDS AND THE FLU

Vitamin D insufficiency is a major health problem worldwide with over one billion people affected across all ethnicities and age groups. Even those living in tropical countries with lots of sun exposure, or in developed countries where vitamin D fortification of foods is prevalent, deficiency exists. ^{1, 2}

Over the last few decades, understanding of vitamin D has changed from merely a vitamin involved in bone metabolism, to a more complex micronutrient with multiple physiological functions, including the modulation of cell growth, inflammation, neuromuscular and immune functions. ^{3, 4, 5, 6}

WE ALL NEED A LITTLE SUNSHINE

We can obtain vitamin D from diet, or from synthesis in the skin by exposure to ultraviolet B (UVB) irradiation from the sun.

Dietary sources of vitamin D include fatty fish, cod liver oil, eggs, milk, mushrooms, liver, and fortified foods. Exposure to UVB solar radiation, however, is the main source of vitamin D for the majority of the population. ^{5, 6, 7}

WHY IS THE FLU SEASONAL?

We all know that colds and flu tend to occur in the winter months. In 1981, a British doctor, Robert Edgar Hope-Simpson, proposed that a “seasonal stimulus” directly associated with solar radiation may explain the seasonality of epidemic influenza.

This association was highlighted a quarter of century later when studies found that vitamin D status may be the “seasonal stimulus” for influenza.^{10, 21}

Wintertime vitamin D deficiency, due to lack of sun exposure on bare skin, has profound effects on the immune system, and thus on susceptibility to infectious diseases. ¹⁰

Surprisingly, the immune-enhancing effects of UVB radiation had been recognized more than a century ago. Unknowingly, vitamin D was used to treat tuberculosis before antibiotics for tuberculosis were discovered. People with tuberculosis were treated with sun therapy.¹⁶ Cod liver oil (a rich source of vitamin D) was also used to treat tuberculosis, as well as to increase resistance to infections.¹⁶

Recently studies have proved this link between tuberculosis and deficiency of vitamin D.^{22, 23, 24, 25, 26} Clinical trials found that vitamin D supplementation could reduce the risk of tuberculosis infection, and high doses of vitamin D with antibiotic treatment may help tuberculosis patients recover faster.^{17, 29}

WHAT DO SCIENTIFIC STUDIES SHOW?

Studies found strong associations between low serum concentrations of 25-hydroxyvitamin D (a marker metabolite of vitamin D and susceptibility to acute respiratory tract infection. ^{9, 10, 11, 20}

Using Third National Health and Nutrition Examination Survey (NHANES III) data, researchers found that upper respiratory tract infection was reported by 40 percent more individuals deficient in vitamin D compared to individuals with adequate vitamin D status.¹⁸

Another study found that soldiers with lower levels of serum 25-hydroxyvitamin D had a 63% increased risk of absence from duty due to respiratory tract infections than did soldiers with higher 25-hydroxyvitamin D levels. ²⁰

Studies proved that vitamin D supplementation may help protect against infections. 25-hydroxyvitamin D supports the synthesis of antimicrobial peptides in response to both viral and bacterial infection. ^{9, 10, 12, 13, 14, 15}

A review of 25 trials showed that vitamin D supplementation may boost immunity and cut rates of respiratory tract infections.⁹

One study found 70 % less incidence of cold and influenza symptoms were reported by those receiving 800 to 2000 IU of vitamin D daily during a 3-year follow-up, compared with the control group. Only one subject had cold/influenza symptoms while taking high doses of vitamin D (2000IU/day). ^{21, 30}

Source: (Aloia et al., 2007), (Aloia et al., 2005)

DOSAGE

Official recommendations for adults: ³¹

In the Endocrine Society Clinical Practice Guideline, researchers suggested “that all adults who are vitamin D deficient be treated with 50,000 IU of vitamin D₂ or vitamin D₃ once a week for 8 weeks or its equivalent of 6000 IU of vitamin D₂ or vitamin D₃ daily to achieve a blood level of 25-hydroxyvitamin D above 30 ng/ml, followed by maintenance therapy of 1500–2000 IU/d.” ^{33, 34}

According to Institute of Medicine (US) (similarly to the European Food Safety Authority EFSA) a tolerable upper intake level for adults is up to 4000 IU.^{31, 35}

Endocrine Practice Guidelines Committee recommends for patients at risk for vitamin D deficiency to set a UL of 10,000 IU/day.^{31, 33}

(Tolerable upper intake level (UL) is the maximum level of total chronic daily intake of a particular nutrient judged to be unlikely to pose a risk of adverse health effects.)

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