PneumoniaPatient friendly summary

  • Pneumonia is more common in winter. There is less UVB light and lower vitamin D levels.
  • Taking 1000-5000 IU/day vitamin D during the flu season greatly lowers the risk of flu and pneumonia.
  • Taking extra vitamin D can strengthen the body’s immune system.
  • A strong immune system may prevent or lower the risk of pneumonia. It may also reduce symptoms.

Pneumonia is an inflammation of the lung. It is usually caused by an infection due to bacteria, viruses, or fungi. Pneumonia can also occur after accidentally inhaling a liquid or chemical.

The symptoms of pneumonia include a cough with mucus, fever, and shaking chills. People often have shortness of breath when they move. Pneumonia is the primary cause of death after a flu.

Risk factors

Those at greatest risk for pneumonia are:

  • Infants, especially those who are premature or have low birth weight (Nearly 75% of deaths caused by pneumonia occur in infants under 1 year of age.)
  • Children younger than 2 years of age
  • Children with human immunodeficiency virus (HIV)
  • Children with rickets and adults with low vitamin D levels
  • People older than 65 years of age
  • People who already have health problems (malnutrition, malaria, suppressed immunity, and respiratory infections or flu)
  • People who live in a health care facility

Sunlight exposure and pneumonia risk

Several studies found that low ultraviolet-B (UVB) exposure and low vitamin D levels caused rickets and pneumonia in children.

According to a study in Philadelphia, pneumonia is most common in winter. Solar UVB doses are lowest then. The effect may be more noticeable in younger people.

During 1918–1919, there was an influenza pandemic in the United States. Death rates were lower in southern cities than in northern cities.

Vitamin D and pneumonia

Vitamin D levels

Studies of vitamin D have occurred around the world. In Yemen, children with vitamin D deficiency (levels less than 10 ng/mL [25 nmol/L]) and rickets had poorer survival rates.

How vitamin D works

To aid the body’s immune system, vitamin D:

  • Produces cathelicidin and defensins: These proteins have antiviral effects to combat viruses and antibacterial effects to fight pneumonia. They may also neutralize bacterial toxins.
  • Reduces inflammation: As a result, the lining of the lungs is less disturbed. This makes it harder for bacteria to grow and cause pneumonia.


High levels of vitamin D may prevent or lower the risk and symptoms of pneumonia.

Based on studies, the risk of influenza and other respiratory infections may be lowered by:

  • 1000–5000 international units (IU) (25–125 mcg)/day of vitamin D, especially during the winter
  • Vitamin D levels above 40 ng/mL (100 nmol/L)


Taking 10,000 IU/day or more vitamin D for a short time strengthens the immune system. This allows the body to fight respiratory infections including pneumonia.

Find out more...

Do you want to find out more and see the research upon which this summary is based?  Read our detailed evidence summary on Pneumonia.

Page last edited: 06 May 2011