A young patient struggling to manage her blood sugar levels despite regular exercise and a clean diet led one doctor to uncover a hidden problem affecting many people with diabetes or prediabetes: poor sleep and excessive caffeine.
Although she had adopted a healthier lifestyle, the patient reported feeling exhausted after her workouts. Meanwhile, her blood sugar levels continued to climb. When asked about her sleep habits, she admitted to sleeping only about five hours a night, sometimes less. To stay alert and meet daily deadlines, she relied on five to six cups of black coffee a day.
This combination, doctors say, is a recipe for blood sugar spikes.
How Sleep Affects Blood Sugar
Getting less than six hours of sleep each night can disrupt the body’s natural ability to manage glucose. Poor sleep increases stress in the body, raising levels of cortisol—a hormone that interferes with insulin, which helps regulate blood sugar.
Even without changes in diet, sleep deprivation can lead to higher blood glucose. It reduces insulin sensitivity and may prompt the liver to release more sugar into the bloodstream in response to perceived stress.
When Coffee Becomes a Problem
While moderate black coffee—one to two cups a day—can be safe or even beneficial for some people with diabetes, too much can cause harm. High doses of caffeine increase both adrenaline and cortisol, which can worsen insulin resistance. When combined with inadequate sleep, the effects on blood sugar are magnified.
Excess caffeine can also interfere with sleep quality, leading to a cycle of sleep deprivation, stress, and rising blood sugar. Studies show that in people with prediabetes or type 2 diabetes, high caffeine intake can reduce insulin sensitivity, increasing the risk of hyperglycemia.
Better Habits, Better Control
To improve blood sugar control, health experts recommend aiming for at least seven to eight hours of sleep each night. Caffeine intake should be limited to no more than two cups per day, ideally consumed before 2 p.m.
By making these small adjustments, many people may see noticeable improvements in blood sugar levels within one or two weeks. These changes can make a significant difference for anyone at risk for diabetes or working to manage it.
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