Vitamin C deficiency has been associated with frequency and duration of colds, along with immune system defects. While colds aren’t usually dangerous in themselves, they can lead to pneumonia and other respiratory diseases, especially for aging individuals. Colds can be an early indicator of gaps in immune function that could leave one vulnerable to a cascade of serious infections.
A deficiency of vitamin C broadly affects the various key aspects of immune function, which include the innate system we are born with, the adaptive system that develops from infancy to young adulthood, the cells that kill invaders, the cells that coordinate those attacks, and even the production of antibodies that fight known infections.
As a result of vitamin C’s wide-ranging impact on the immune system, a deficiency could leave us vulnerable to infections. A weakened immune system caused by low vitamin C levels can make any infection more serious. This danger becomes more ominous in older adults, in whom the phenomenon of immunosenescence (the aging of the immune system) already heightens risk.
There are multiple causes of insufficient vitamin C. Aging is one major cause of lowered vitamin C levels. The concentration of vitamin C in immune cells decreases with age, partly the result of an increasingly oxidative environment that consumes vitamin C. This can lead to damage to DNA, proteins, and fat molecules needed for normal immune function.
Stress is another major trigger for reducing vitamin C levels, leaving the affected individuals vulnerable to infection at precisely the time that stronger immune support is needed. In some remarkable human findings, low vitamin C blood levels have been associated with a number of common human diseases. The table below shows higher plasma vitamin C levels in healthy individuals compared to those with serious diseases, most notably cancer and sepsis.
One of the most important functions of vitamin C is to support and energize the body’s immune system. Immune cells have active vitamin C transporter molecules embedded in their membranes that actively pump the vitamin into the cells when more vitamin C is required.
For example, during times of inflammation or infection, those transporters ramp up their activity to provide sufficient vitamin C to the cells’ inner workings, causing cells to attain levels up to 100-fold that of the plasma level. This is why blood levels of vitamin C drop during times of disease or infection.
This can create a potentially vicious cycle in which, just when you need extra vitamin C, your body’s stores are depleted. This also makes it especially important to increase one’s intake of vitamin C when sick.
The content of vitamin C within immune cells is closely related to those cells’ activity, especially in the case of specific cells that engulf and destroy infecting organisms (phagocytes) and of those that recruit, organize, and direct other immune cells.
Fortunately, you can improve your immune system’s function by supplementing with vitamin C. The recommended daily allowance of vitamin C is around 90 mg per day. For optimal immune function, many experts now recommend supplementing with 1 gram (1,000 mg) of vitamin C daily in addition to a diet rich in fruits and vegetables.
Human studies have shown that this amount of vitamin C can not only reduce the duration and severity of the common cold—but can reduce the incidence of developing a cold as well. Not all common cold studies produce consistent results. This means more than vitamin C alone is needed to combat common colds, such as using the right dose of zinc acetate lozenges as soon as cold symptoms manifest.