A recent animal study suggests vitamin A and D deficiency may reduce the efficacy of flu vaccines.
Influenza, also known as the flu, is a contagious respiratory infection caused by the influenza virus. The severity of the flu varies from year to year with annual mortality rates ranging from 3,000 to 49,000 in the U.S.
In order to prevent the flu from spreading, many scientists and health professionals advocate the flu vaccine. Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. Antibodies are proteins that recognize and battle foreign substances, such as viruses, that have invaded the blood.
If an individual receives the flu vaccine, their immune system will recognize the influenza virus and immediately creates more antibodies to fight it. However, this only occurs if the flu vaccine accurately matches the flu virus for that particular season, and if the person has a healthy immune system. With that being said, the Center for Disease Control and Prevention estimates that the vaccine is effective 50-60% of the time.
Flu season peaks during the winter, which is also the time of the year when vitamin D levels are at the lowest. In addition, vitamin D helps the immune system function optimally; meaning vitamin D status could possibly be related to the effectiveness of the influenza vaccine.
Evidence also suggests that vitamin A may play a role in the flu. In an animal study, researchers discovered that mice with an absence of vitamin A experienced a significantly weakened immune response toward virus vaccines.
In a new study, the same research team investigated whether double deficiencies for vitamins A and D would exacerbate impaired immune responses to influenza vaccines in mice.
The researchers compared the efficacy of influenza vaccines in four groups of mice: vitamin D deficient (VDD) mice, vitamin A deficient (VAD) mice, vitamin A and D deficient (VAD+VDD) mice, and lastly, vitamin A and D sufficient (control) mice.
To establish vitamin deficient mice, pregnant mice were administered special diets. Then, the pregnant mice gave birth to mice with similar nutrient profiles. The offspring adhered to the same diet as their mothers to ensure they remained deficient or sufficient in the appropriate vitamins. The researchers also measured vitamin A and D levels in all of the mice to confirm their vitamin status. Both the male and female offspring were used in the experiment once they reached the age of 6 weeks or older.
The mice received influenza vaccines. Then, they were administered (1) no vitamin supplement, (2) vitamin A supplements and/or (3) liquid vitamin D3.
Approximately one month after vaccination, mice were assessed for influenza virus-specific antibodies. Antibody levels were significantly lower in VDD mice compared to controls. However, the difference in antibody levels was even greater when comparing the control mice to the VAD mice. VAD+VDD mice experienced the most impaired immune response to the vaccine, showing the lowest levels of antibodies.
Next, the researchers wanted to determine if the weakened antibody responses seen in the VAD+VDD mice could be corrected with vitamin supplementation. The researchers administered vitamin D and/or vitamin A supplementation to the VAD+VDD mice. Vitamin A supplementation alone improved antibody levels greater than vitamin D supplementation alone. However, the greatest improvement was observed in the mice that received both vitamin A and D as supplements.
The researchers concluded,
“Relative to VAD, vitamin D deficiency (VDD) had a limited effect, but double deficiencies for vitamins A and D (VAD+VDD) reduced immune responses in the respiratory tract. The administration of supplemental vitamins A and D to VAD+VDD mice at the time of vaccination restored responses in a dose-dependent manner.”
They went on to state,
“Results suggest that vitamin supplementation programs may be beneficial in a clinical setting to promote healthy immune responses toward respiratory virus vaccines in vitamin deficient individuals.”
While this study provides interesting findings, it’s important to emphasize that the study occurred in animals. Clinical trials are needed to evaluate whether vitamin A and D sufficiency plays a role in the efficacy of flu vaccines in humans.
The Vitamin D Council recommends supplementing with 5,000 IU of vitamin D3 on days that one cannot receive adequate, safe sun exposure. However, we do not advocate exceeding the recommended dietary allowance (RDA) for vitamin A, as it can easily become toxic. Vitamin A can also interact with various medications, so before taking a supplement, one should speak to a physician.
Tovey, A. & Cannell, JJ. Animal study suggests vitamins A and D may relate to the effectiveness of flu vaccines. The Vitamin D Council Blog & Newsletter, January, 2016.
Surman, SL. et al. Vitamin supplementation at the time of immunization with cold-adapted influenza virus vaccine corrects poor antibody responses in mice deficient for vitamins A and D. Clinical and Vaccine Immunology, 2016.