Secretory immunoglobulin A (sIgA) deficiency is a less known but a significant aspect of having good immunity and a well-functioning digestive system, to name a few.

I’ve long been interested in sIgA’s role in health and wellbeing, and would like to shed some light on this subject based on my clinical experience and research. The importance of sIgA for effective immune defence is indicated by the fact that more sIgA is produced than all the other immunoglobulin classes combined. 

Despite the importance of sIgA for health, it’s one of the least well-understood areas of immunology.

What is Secretory Immunoglobulin A (sIgA)?

The body’s mucosal surfaces such as those of the nose, throat, eyes and gastrointestinal tract (GIT) are a large point of entry for various pathogens and thus must be well protected by the body.

The primary antibody/ immune system response to these irritants at the mucosal level is sIgA produced by the B lymphocytes (immune system cells) present in all mucosal linings.

sIgA acts as the ‘first line of defence’ helping to protect against the entrance of foreign substances or organisms into the body such bacteria, viruses, fungi, parasites and food particles (via the damaged gut wall caused by the leaky gut syndrome).

The immune system responds to the protein component (antigens) of these invaders by producing large quantities of specific antibodies, including sIgA. These antibodies bind to the antigens on the surface of an invader (bacteria, for example) and prevent them from multiplying, thus halting the spread of disease in the body.

This mechanism works well when the GIT is healthy and sIgA levels are normal.

The daily production of sIgA is weight and age dependent with the maximum production level being reached at the age of 7-10 which then declines with age, especially after 60 years of age. It’s been calculated that around 60 mg of IgA is produced per kilogram of body weight per day in the average human, mainly in the mucosal