The pancreas, which is responsible for making and releasing the hormone insulin, is especially sensitive to melatonin levels. While melatonin levels are high during nighttime hours, insulin levels are at their lowest. Melatonin binds to receptors in the pancreas and cause a slowdown in insulin production while you’re asleep. This makes sense when you think about the role of insulin.
And, since you’re in a period of fasting during sleep, low levels of insulin at night actually help keep blood sugar levels stable, preventing hypoglycemia, until you eat again the next day.
If melatonin levels are low, then the suppression of insulin activity at night is also decreased. This means your pancreas doesn’t get a nightly rest from producing insulin.
When insulin levels are elevated around the clock, your pancreas can become inefficient at making enough insulin and/or the cells in the rest of your body can become desensitized in response to exposure to too much insulin. This is known as insulin resistance. It results in increased blood sugar levels and is a major risk factor in developing type 2 diabetes.