Immunoglobulin A is the first line of defense against harmful microbes, but it also maintains your immune tolerance. Low levels increase the risk of allergies and autoimmunity. Read on to find out what low IgA levels or selective IgA deficiency may imply.
Low IgA Levels
Lower IgA may imply your immunity is weakened. Also, recent research findings now hint that it may indicate a disturbed intestinal barrier and/or gut microbiota imbalances [1, 2, 3].
In adults, IgA values below 60 mg/dL are considered low by most labs. Remember to discuss your lab results with your physician.
Chronic stress, poor sleep, and exhaustion decrease IgA in the saliva where the first defense function is needed. A blood IgA tes alone will not reveal this lowered immune response [4, 5, 6, 7].
Having low IgA increases the risk of allergies, infections, and autoimmune diseases [8, 9, 10, 11].
Low serum IgA can be found in individuals with:
- Chronic gut disorders (IBS, IBD) [12, 13]
- Food and respiratory allergies [8, 14]
- Autoimmune disease (celiac disease, type 1 diabetes) 
- Some infections, such as Epstein-Barr virus infection 
- Rare disorders such as hereditary telangiectasia 
- Some tumors [18, 19]
Drugs that can reduce IgA levels include:
- Chemotherapeutics, especially in patients with leukemia [20, 21, 22]
- Sulfasalazine (Azulfidine, Salazopyrin, Sulazine), a drug used to treat rheumatoid arthritis and ulcerative colitis 
- Phenytoin (Dilantin), used to treat seizures 
Symptoms & Diseases Associated with Low IgA
85 to 90% of people with IgA deficiency have no symptoms. Instead, they may only show symptoms from their underlying infections or immune disorders .
Allergies, Asthma & Autoimmunity
IgA protects against allergies.
IgA levels are reduced in children with allergic rhinitis. Lower levels were associated with more severe symptoms .
IgA in breast milk may protect against atopic dermatitis in infants. One study found that IgA ingested in breast milk during the first year of life reduced the risk of atopic dermatitis up to age 4 .
Also, higher blood IgA levels were associated with a lower frequency of eczema at 18 months of age .
Furthermore, higher levels of IgA in infants seemed to correlate with less developing allergies at the age of 4 .
High IgA levels in saliva were associated with less allergic symptoms in children .
In patients allergic to cow’s milk, those who naturally developed tolerance had increased blood IgA levels .
Low IgA levels were found in the lungs of severe asthmatics. Lower IgA levels were associated with more severe symptoms .
However, in severe asthma, IgA may aggravate the existing inflammation instead of promoting tolerance .
Other autoimmune diseases, such as hemolytic anemia, type 1 diabetes, rheumatoid arthritis, thyroid disorders, and lupus are also more frequent in IgA-deficient people [25, 11].
IgA-deficient people more often have allergies, including asthma, allergic rhinitis/conjunctivitis, drug allergy, or food allergy .
They also have a higher prevalence of atopic dermatitis, acne, and chronic spontaneous hives .
There is no specific treatment for this condition (such as immunoglobulin replacement used for other immune deficiencies). Antibiotics are prescribed in those with bacterial infections and are very important to prevent serious complications .
First-degree relatives of IgA-deficient patients also have an increased risk of autoimmunity (10% compared to an estimate of 5% in the general population) .
Risk of Infections
IgA protects the lungs and the gut against invading harmful microbes.
People with IgA deficiency are at a higher risk for infections, including infections of the respiratory system, gut, joints, and urinary tract .
Prolonged exercise decreases IgA. Suppressed IgA was associated with an increase in respiratory infections in ultramarathoners .
Medication-free patients with major depression had a significant reduction in blood IgA levels in the remitted state (when they were symptom-free) .
Even in healthy people, IgA was reduced when participants recalled events that made them depressed .
The research on IgA and autism is mixed. Autism is more prevalent among IgA deficient subjects and their relatives .
A study showed an association between autism with low normal IgA (<97 mg/dL) .
However, another study did not find lower IgA levels in autistic people .
Obesity and Metabolic Syndrome
The research on IgA and obesity is also mixed and inconclusive.
Obese individuals were shown to have higher IgA levels in the blood than people with normal weight .
In the same study, blood IgA levels were also higher in those with metabolic syndrome. This includes people with elevated triglycerides, high blood sugar, or high blood pressure .
However, other studies found normal IgA levels in obese people, and even low levels in obese children [41, 42, 43].
Such conflicting research may be due to the fact that there is no one cause of obesity. Some underlying factors triggering obesity may increase IgA levels while others may decrease them. Additional studies should clarify this link.
Selective IgA Deficiency
Low IgA can be caused by selective IgA deficiency, when only IgA levels are low but other antibodies (IgG, IgM, IgD, and IgE) are normal .
Selective IgA deficiency can be inherited or occur spontaneously (due to infections, medication, or unknown causes) . The genetic disorder that causes people to lack IgA is found in up to 1% of the population.
IgA deficiency is the most common primary immunodeficiency. Prevalence is higher in whites (1:155 in Spain, around 1:500 in general) and lower in Asians (1:18550 in Japan) [44, 33].
People are IgA deficient if they have blood IgA levels below 7 mg/dL with normal IgM and IgG levels .
Eighty-five to 90% of people with IgA deficiency have no symptoms. Those with symptoms usually have respiratory or gut infections [25, 33].
Infections & Celiac Disease
IgA-deficient people have a tendency to develop infections and disorders of the gut, such as malabsorption, lactose intolerance, celiac disease, and ulcerative colitis [25, 33].
Risk of Autoimmune Diseases
Patients with selective IgA deficiency (undetectable IgA but normal IgG and IgM levels) have a 10 to 20 times higher risk of celiac disease .
Multiple studies report an increased prevalence of IgA deficiency in patients with celiac disease and increased prevalence of celiac disease in patients with IgA deficiency [46, 15].
People with IgA deficiency have a higher association of type 1 diabetes (up to 10 times), lupus, juvenile idiopathic arthritis, IBD (both Crohn’s and ulcerative colitis), rheumatoid arthritis, and thyroid disorders .
IBS & IBD
In a pilot study with 12 IBS patients and 11 healthy controls, those with IBS had less IgA-producing cells . Though it should be remembered that this study was very small and needs more follow up.
IBD is associated with IgA deficiency [25, 11].
In ulcerative colitis in Crohn’s patients, IgA production in the gut was decreased [13, 47].
Low IgA has been found in up to 8% of IBD patients .
However, higher IgA production in the gut may cause IBD .
Bacteria coated with a high level of IgA may be responsible for gut inflammation in patients with IBD. IgA-coated bacteria increase gut inflammation when transplanted into mice with ulcerative colitis .
Those with IgA deficiency have a moderately increased risk of cancer, especially gut cancer .
This study was done as a cohort and showed risk increases in first year of follow up suggesting surveillance bias. More studies are needed to conclude degree of cancer risk.
IgA is an important player in immune defense and tolerance. Low levels usually mean the immune system is weakened. Low IgA levels and IgA deficiency are not the same. Any IgA value below 60 mg/dL is considered low by most labs, but only values below 7 mg/dL imply deficiency. Symptoms depend on the underlying cause.
Chronic stress, poor sleep, exhaustion, and certain genetic disorders may all lead to low IgA levels or deficiency. Though more research is needed, some studies have also linked low IgA with infections, allergies, autoimmunity, and gut disorders.