Understanding Insulin Production in the Brain

Interestingly, your brain is capable of producing insulin, which is the same type that your pancreas produces. This is particularly relevant for those with type 1 diabetes, who lack insulin production, and for individuals with type 2 diabetes, where insulin doesn’t function correctly.

For over a century, scientists have been aware of insulin-producing cells found in the pancreas. These clusters of cells, known as islets, contain beta cells responsible for insulin production.

However, our understanding of insulin production in the brain is still quite limited. The fact that insulin is produced here isn’t widely recognized, even among diabetes specialists and individuals living with diabetes.

This discovery dates back to the late 1970s but was largely overlooked. A study from 1978 reported that insulin levels in the brains of rats were significantly higher—ten times more than in their blood, and in some brain regions, even a hundred times more.

If that’s the case, why isn’t this information more prevalent?

Following that discovery, evidence emerged showing insulin’s transition from blood to brain. A 1983 study noted that insulin observed in the brain of rodents was traced back to pancreatic insulin, but researchers struggled to identify the means for insulin processing in the brain using the available tools of that time.

This led to a prevailing assumption for nearly three decades that all brain insulin originated from the pancreas.

While it’s true that insulin can move from blood to brain, local sources of insulin exist that serve specific functions.

The Brain Cells That Produce Insulin

What’s intriguing here is that there isn’t just one type of insulin-producing cell in the brain, but at least six. Some have been identified in both rodent and human brains, while others are still only confirmed in rodents.

A notable type of insulin-producing brain cell is the neurogliaform cell, found in regions crucial for learning and memory. Surprisingly, the insulin produced by these cells relies on glucose levels—similar to pancreatic beta cells.

The precise role of this insulin is still uncertain, though it might have implications for cognitive function. Interestingly, this area also contains neural progenitors, which are cells that can form new neurons throughout life, and these cells also produce insulin.

Another insulin-producing cell is located in the olfactory bulb, which is key for processing smells. The functions of insulin in this context, however, remain a mystery.

There’s also a type of brain cell that appears to regulate growth, as evidenced by a 2020 study showing insulin produced in the hypothalamus, a region controlling growth and metabolism. Stressing out mouse subjects led to reduced hypothalamic insulin production, resulting in stunted growth.

Furthermore, the hypothalamic insulin plays a role in maintaining growth hormone levels, which are vital in the overall hormonal balance of the body.

Then we have the choroid plexus, the area of the brain responsible for producing cerebrospinal fluid. This region is capable of generating a nourishing mix of growth factors and nutrients to support brain health, and recent findings have confirmed that insulin is produced here in mice.

The choroid plexus releases its fluid into the brain’s ventricular system, potentially helping to distribute insulin more broadly within the brain.

This insulin does make its way to the appetite control center in the hypothalamus.

A recent study from 2023 highlighted how alterations in insulin production from the choroid plexus could influence food intake, revealing that insulin released from this area can suppress appetite.

Another source of insulin found in the brain also appears to help reduce food consumption. Research from 2022 reported that insulin-producing neurons in the hindbrain contributed to reducing food intake in mice.

The Role of Insulin in Brain Health as We Age

So, if brain insulin has the ability to change appetite, what about its influence on blood sugar levels?

Currently, there’s no evidence suggesting that it affects blood sugar in the same way. It seems unlikely that brain insulin leaves the brain, so it probably doesn’t control glucose levels like pancreatic insulin does.

Instead, brain insulin may play a role in supporting brain health as we age. Alzheimer’s disease is often referred to as type 3 diabetes informally, since insulin resistance occurs in the brain as part of the disease process, impairing the proper use of glucose.

This poses a significant issue since glucose serves as the brain’s main energy source. Estimates indicate there might be a 20% energy deficit in individuals with Alzheimer’s, leading to cognitive impairments even without the loss of brain cells.

This has spurred interest in attempts to enhance brain insulin levels. Some studies have suggested that administering insulin through the nasal route can improve cognitive performance in certain Alzheimer’s patients.

Interestingly, brain glucose utilization tends to decrease with age, but intranasal insulin may help mitigate this decline.

So, does having more brain insulin equate to better outcomes?

Not necessarily. In particular, higher levels of insulin in cerebrospinal fluid are linked to poorer cognitive performance in women.

There’s much left to uncover about brain insulin production—like which came first, brain or pancreatic insulin production? Let’s hope it doesn’t take another few decades to get some answers.

By piecing together the evidence of brain insulin production, it seems pretty likely that we’ll see updates in school textbooks sooner rather than later.