The hemoglobin A1c test, known as A1c, provides a picture of your average blood sugar levels over the past two to three months. It measures the percentage of your hemoglobin—a protein in red blood cells that carries oxygen—that is coated with sugar. While high A1c levels are a recognized indicator for diabetes, research is exploring the link between low A1c levels and cancer. A low A1c is considered below 5.0% and, while often a sign of good health, may warrant further investigation.
The Association Between Low A1c and Cancer
Observational studies have identified a correlation between low A1c values and an increased risk for certain cancers. These findings show an association, not a direct causal relationship. Research points to a U-shaped curve in the relationship between A1c and cancer risk, where both very high and very low levels are associated with higher incidence rates. For instance, one large study found that individuals with A1c levels below 5.0% had an increased risk of death from cancer compared to those in the normal range.
The connection is more pronounced for specific types of cancer, with some research indicating a link between low A1c and an increased risk for liver cancer. This is distinct from other cancers, like pancreatic cancer, where a low A1c was associated with a lower risk. The data on other cancers, such as breast and colorectal, have been less consistent.
The association can also be influenced by factors like age, smoking, and body mass index (BMI). Study duration is relevant, as short follow-up periods might include undiagnosed cancers that are influencing A1c levels, rather than the other way around. This makes it difficult to draw firm conclusions about a direct link.
Potential Reasons for the Link
One hypothesis is “reverse causation,” which suggests the low A1c is a consequence of an undiagnosed tumor, not a cause of cancer. Cancer cells have a high metabolic rate and consume large amounts of glucose to fuel their growth. This increased glucose uptake by a tumor can lower overall blood sugar levels, resulting in a low A1c reading. Cancer can also cause physiological changes, such as malnutrition and muscle wasting, that alter metabolism and further lower blood glucose.
Another explanation involves confounding factors, where an underlying health condition causes both the low A1c and the increased cancer risk. Chronic liver disease is an example. The liver plays a role in regulating blood glucose, and if its function is impaired, it can lead to lower A1c levels. At the same time, chronic liver conditions are known risk factors for liver cancer. In this scenario, the liver disease is the common factor causing both outcomes.
Low A1c in People With and Without Diabetes
For individuals without diabetes, a low A1c reading can prompt a healthcare provider to investigate underlying health issues. Because this group is not taking glucose-lowering medications, a low A1c could be a sign of liver disease, malnutrition, or an undiagnosed cancer. It signals the need for further evaluation to identify any root causes that require medical attention.
The interpretation of a low A1c is different for a person being treated for diabetes, where it often indicates that blood sugar is well-managed. However, an extremely low A1c might suggest the treatment plan is too aggressive. Intensive medication can lead to frequent episodes of hypoglycemia, a condition where blood sugar drops to unsafe levels.
A person with diabetes who has a very low A1c reading should speak with their doctor. It may be necessary to adjust their medication, diet, or exercise regimen to prevent hypoglycemia while maintaining good glycemic control.