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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Influenza

woman with tissue

Summary

Influenza, more commonly known as the flu, is a respiratory infection that is caused by a virus infecting the nose, throat, and lungs. Influenza is most common during winter and can cause fever, chills, sore throat, cough, body aches, and fatigue.

Vitamin D is an important part of the immune system. Some studies have shown that there is a link between vitamin D levels and the risk of getting influenza. People who have low vitamin D levels may have a higher chance of developing influenza.

Influenza epidemics occur in the winter, and vitamin D levels are dramatically lower in the winter as well. Since influenza is seasonal, it is thought that vitamin D might be a factor that can affect your chances of getting the flu.

Many studies that have been done about influenza have shown that people who have lower levels of vitamin D are more likely to get influenza. Not many studies have been done about treating influenza with vitamin D, but some research has shown a relationship between higher levels of vitamin D and shorter duration of the influenza infection.

On the other hand, some experiments have shown that taking vitamin D supplements can reduce your chances of getting influenza in the first place. Some researchers recommend getting more vitamin D to protect against influenza, but more experiments are needed to say whether or not taking a vitamin D supplement can for sure prevent influenza.

If you want to take vitamin D to prevent influenza, it is unlikely to cause you any harm, as long as you take less than 10,000 IU per day. However, it’s not proven that taking vitamin D will help to prevent or treat influenza.

If you have influenza, you shouldn’t take vitamin D in place of your treatment medications. Talk to your physician for more advice about taking supplements.

What is influenza?

Influenza, also known as the flu, is a respiratory infection that is caused by the influenza virus and infects the nose, throat, and lungs. Influenza is contagious and is more common during winter. In the United States, the peak of flu season is generally from late November through March, but it has been known to last until May. Young children, the elderly, and people with chronic diseases are more likely to have severe complications from getting the flu. Influenza can cause hospitalization or death in serious cases1.

Since the common influenza viruses change every season, so do the vaccines. Each flu season is different depending on what viruses are spreading quickly, how many people get the vaccine, and if the vaccine is correctly matched to the influenza virus that are causing the most illness. Getting a flu vaccine is a way to protect against getting infected with influenza1.

The three types of influenza are types A, B, and C. Types A and B are the viruses that are typically responsible for seasonal influenza epidemics. Type C influenza viruses can cause a mild respiratory infection, but this virus generally does not cause flu epidemics. There are also subtypes of type A influenza viruses, which are based on 2 proteins found on the virus (abbreviated H and N). A common example is H1N1. The most common influenza virus in the 2012-2013 flu season was H3N21.

What are the symptoms of influenza?

Someone who is infected with the influenza virus may experience some or all of these symptoms1:

  • Fever or chills
  • Cough
  • Sore throat
  • Muscle, body, and head aches
  • Fatigue
  • Vomiting and diarrhea, which is more common in children with influenza.

Most of the time, a healthy person will recover from influenza in a few days or up to 2 weeks.  Sometimes, people can develop serious complications from influenza, like pneumonia, bronchitis, or sinus and ear infections. Influenza can also make a chronic condition worse, like asthma1. When influenza is fatal, oftentimes it is due to a bacterial infection, like pneumonia, that is secondary to the influenza2.

What are the risk factors for influenza?

For the 2012-2013 flu season, more than half of hospitalizations related to influenza were in adults over age 65.

For the 2012-2013 flu season, more than half of hospitalizations related to influenza were in adults over age 65.

Annually, influenza affects about one-fifth of the U.S. population3. For the 2012-2013 flu season, more than half of hospitalizations related to influenza were in adults over age 65.

People who are at higher risk for developing influenza include1:

  • People over age 65
  • Children, especially those under age 2
  • People with chronic disease, like asthma, diabetes, lung or heart disease
  • People with weakened immune systems, like from cancer or HIV/AIDS
  • People who are morbidly obese
  • Pregnant women
  • American Indians and Alaskan Natives

How does influenza spread?

Influenza is contagious. Someone who is infected with the virus can be contagious 1 day before influenza symptoms develop, and up to 7 days after they are sick. Young children or people with weak immune systems are able to infect others for a longer period of time1.

The influenza virus can spread when someone who is infected coughs, sneezes, or even talks. Droplets containing the influenza virus travel through the air and can be directly inhaled by another person through the mouth or nose. The droplets may also land on a surface and you could pick them up and then become infected after touching your eyes, nose, or mouth1,4.

If you have had influenza before, your body has made antibodies to help protect you against that specific virus in the future. However, because the influenza viruses are changing every year, you won’t have antibodies against the newer virus. Vaccines attempt to have your body make antibodies against the most current influenza virus4.

What is the link between influenza and vitamin D?

Vitamin D is an important part of the immune system. Some studies have shown that there is a link between vitamin D levels and the risk of getting influenza. People who have low vitamin D levels may have a higher chance of getting influenza5.

Vitamin D receptors are found on the surface of a cell where they receive chemical signals. By attaching themselves to a receptor, these chemical signals direct a cell to do something, for example, to act in a certain way, or to divide or die.

There are vitamin D receptors found on cells in the immune system, and vitamin D can bind to these receptors6. Vitamin D works in the immune system by reducing levels of inflammatory proteins called cytokines, as well as increasing amounts of antimicrobial proteins, which destroy invading germs and viruses. This combination of lowering inflammation and increasing antimicrobial defenses can help your immune system fight infections better7,8.

There are two branches of your immune system: the adaptive and the innate. The adaptive immune system develops based on previous exposure to a virus. The innate immune system is the part that can respond quickly to foreign invaders, and is based on the levels of immune cells and proteins you have2,9. It is thought that vitamin D helps to strengthen innate immunity, because it can increase the amounts of good immune proteins10. If you don’t have enough vitamin D, some parts of your innate immunity may not function as well11.

Influenza epidemics occur in the winter, and vitamin D levels in the greater population are dramatically lower in the winter as well12. Since influenza is seasonal, it is thought that vitamin D might be a factor that can affect someone’s chances of getting the flu7.

While it is thought that having enough vitamin D may help to prevent influenza, more experiments need to be done to determine if taking vitamin D supplements can prevent influenza, or make the duration of the illness shorter. Research hasn’t been able to show definitively yet that low vitamin D levels are a cause of influenza.

What does the research say in general about influenza and vitamin D?

Preventing influenza

Most studies that have been done about influenza have shown that people who have lower levels of vitamin D are more likely to get influenza. A study was done that looked at the levels of vitamin D in people with prostate cancer and their immune response to the influenza vaccine. This study found that people who had higher levels of vitamin D had a higher response to the vaccine, meaning that they would be more protected against getting influenza13. However, another study done on people over age 50 found that vitamin D levels didn’t have a significant effect on their immune response to the influenza vaccine8.

Another study found that people with lower levels of vitamin D were twice as likely to develop influenza, compared to people with high levels of vitamin D14.

More experiments are needed to determine whether or not taking a vitamin D supplement can help to protect against getting influenza.

Treating and recovering from influenza

Not many studies have been done about treating influenza with vitamin D, but some research has shown a relationship between vitamin D and the duration of the influenza infection.

Not many studies have been done about treating influenza with vitamin D, but some research has shown a relationship between vitamin D and the duration of the influenza infection.

Not many studies have been done about treating influenza with vitamin D, but some research has shown a relationship between vitamin D and the duration of the influenza infection. Other studies have looked at influenza outcomes, like pneumonia or death, in large influenza epidemics that happened in the past.

A study that looked at the deaths from the large 1918-1919 influenza pandemic found that the lowest influenza-related death rates in the United States were found in the city with the highest amounts of UVB light, which helps you make vitamin D. They also found that the most influenza deaths were in the city with the lowest amounts of UVB light. This suggests that vitamin D may have been an important factor in helping people recovering from influenza, although we can’t know for sure2.

People with enough vitamin D may recover from influenza faster than people with low levels of vitamin D. A study found that people with vitamin D levels above 38 ng/mL recovered from influenza in an average of 2 days, whereas people with vitamin D levels below 38 ng/mL took an average of 9 days to recover from influenza14.

What does recent research say about vitamin D and influenza?

An experiment done in the United States gave African-American women either 800 IU vitamin D per day for 2 years, then 2,000 IU per day for the 3rd year, or a dummy pill. The researchers looked at how many times those women got influenza over the 3 years. They found that15:

  • The vitamin D group had fewer influenza symptoms compared to the dummy pill group.
  • Only one person in the vitamin D group had influenza when the dose was at 2,000 IU per day.
  • The dummy pill group had influenza symptoms mostly in the winter, whereas the people who got influenza in the vitamin D group had symptoms year round.

This experiment suggests that vitamin D, especially at higher doses, may help to protect against seasonal influenza. The researchers conclude that vitamin D supplements might be useful to prevent the flu, but that more experiments are needed.

An experiment done with Japanese schoolchildren looked at the effects of vitamin D supplements on their chances of getting influenza. The researchers gave children either 1,200 IU vitamin D per day for 3 months during the winter, or a dummy pill. They found that16:

  • More children in the dummy pill group got influenza A than children in the vitamin D group.
  • There was a preventive effect of 1,200 IU vitamin D per day on children getting influenza A.

The researchers conclude that taking 1,200 IU of vitamin D in children can help to protect against seasonal influenza A.

In this study, there was no effect of vitamin D on influenza B, possibly because vitamin D may respond in different ways to the inflammatory proteins in the viruses.

A study done in 2011 looked at vitamin D levels and respiratory infections, like influenza, in a large group of British adults. The researchers found that17:

  • For each 4 ng/ml increase in vitamin D levels in the body, there was a 7% lower chance of developing influenza.
  • There was a seasonal pattern of influenza which was the same as the seasonal pattern of vitamin D levels. Influenza infections decreased when vitamin D levels increased.

However, since this study was observational, the researchers couldn’t conclude for certain if higher vitamin D levels protected against the flu.

Key points from the research

  • People who get influenza are more likely to have low levels of vitamin D in their body.
  • Vitamin D can help reduce inflammation caused by the influenza virus and increase the number of proteins that fight against viruses.
  • Influenza infections increase during the winter, which is when vitamin D levels are known to decrease in the population.
  • Some experiments have shown that taking vitamin D supplements can reduce the chances of getting influenza.
  • Having high levels of vitamin D may help you to recover faster from an influenza infection, although we don’t know for sure yet if they do.
  • Some researchers recommend getting more vitamin D to protect against influenza. Still, more experiments are needed for scientists and doctors to clearly understand whether or not taking a vitamin D supplement can prevent influenza.

What does this mean for me?

Influenza epidemics occur in the winter, and vitamin D levels are dramatically lower in the winter as well, so it is thought that vitamin D might be a factor that can affect someone’s chances of getting the flu.

Influenza epidemics occur in the winter, and vitamin D levels are dramatically lower in the winter as well, so it is thought that vitamin D might be a factor that can affect someone’s chances of getting the flu.

Research has shown there is a link between vitamin D and influenza. Vitamin D plays an important role in helping your immune system to fight infections. People who have low levels of vitamin D are more likely to develop influenza.

Influenza epidemics occur in the winter, and vitamin D levels are dramatically lower in the winter as well. Since influenza is seasonal, it is thought that vitamin D might be a factor that can affect someone’s chances of getting the flu.

Some studies have shown that giving vitamin D supplements to people can help to protect them from getting seasonal influenza. More research is needed to see just how effective vitamin D can be in influenza prevention.

If you want to take vitamin D to prevent influenza, it is unlikely to cause you any harm, as long as you take less than 10,000 IU per day. However, it’s not proven that taking vitamin D will help to prevent or treat influenza.

If you have influenza, you shouldn’t take vitamin D in place of your treatment medications. Talk to your physician for more advice about taking supplements.

References

  1. Centers for Disease Control and Prevention. Seasonal Influenza: Flu Basics. 2013. Web. <http://www.cdc.gov/flu/about/disease/index.htm>
  2. Grant WB & Giovannucci E. The possible roles of solar ultraviolet-B radiation and vitamin D in reducing case-fatality rates from the 1918 – 1919 influenza pandemic in the United States. Dermato-Endocrinology 2009;1:215-219.
  3. Rees, J. Vitamin D3 supplementation and respiratory tract infections in a randomized controlled trial. Clinical Infectious Diseases 2013;57(10):1384-1392.
  4. Mayo Clinic. Influenza (Flu). 2014. Web. < http://www.mayoclinic.org/diseases-conditions/flu/basics/causes/con-20035101>
  5. Laaski I, Ruohola JP, Tuohimaa P, et al. An association of serum vitamin D concentrations <40 nmol/L with acute respiratory tract infection in young Finnish men. American Journal of Clinical Nutrition 2007;86:714-717.
  6. Lang PO & Samaras D. Aging Adults and Seasonal Influenza : Does the Vitamin D Status ( H ) Arm the Body? Journal of Aging Research 2012;2012:1-9.
  7. Cannell JJ, Vieth R, Umhau JC, et al. Epidemic influenza and vitamin D. Epidemiolo Infect 2006;134:1129-1140.
  8. Sundaram MA, Talbot HK, Zhu Y, et al. Vitamin D is not associated with serologic response to influenza vaccine in adults over 50 years old. Vaccine 2013;31:2057-61.
  9. Cannel  JJ, Zasloff M, Garland CF, et al. On the epidemiology of influenza. Virology Journal 2008;12:1-12.
  10. Mascitelli L, Grant WB & Goldstein M. Obesity, Influenza Virus Infection, and Hypovitaminosis D. Journal of Infectious Diseases 2012;206:1481-2.
  11. Yusupov E, Li-Ng M, Pollack S, et al. Vitamin D and Serum Cytokines in a Randomized Clinical Trial. International Journal of Endocrinology 2010:2010;1-7.
  12. Khare D, Godbole N, Pawar SD, et al. Calcitriol [1, 25[OH]2 D3] pre- and post-treatment suppresses inflammatory response to influenza A (H1N1) infection in human lung A549 epithelial cells. European Journal of Clinical Nutrition 2013:52;1405-15.
  13. Chadha M, Fakih F, Muindi J, et al. Effect of 25-Hydroxyvitamin D Status on Serological Response to InfluenzaVaccine in Prostate Cancer Patients. The Prostate 2011;71:368-372.
  14. Sabetta J, Depetrillo P, Cipriani R, et al. Serum 25-Hydroxyvitamin D and the Incidence of Acute Viral Respiratory Tract Infections in Healthy Adults. PLoS One 2010;5(6):e11088.
  15. Aloia J & Li-Ng M. Re: epidemic influenza and vitamin D. Epidemiology 2007;135(7)1095-6.
  16. Urashima M, Segawa T, Okazaki M, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. American Journal of Clinical Nutrition 2010;91:1255-60.
  17. Berry D, Hesketh K, Power C, et al. Vitamin D status has a linear association with seasonal infections and lung function in British adults. British Journal of Nutrition 2011;106:1433-1440.

This page was last updated March 2014.

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