Late nights risk blood sugar control, study finds: Less than 'this many' hours sleep increases diabetes risk

Late sleeping habits can significantly destabilize blood sugar levels by interfering with the body's circadian rhythm, hormones, and insulin sensitivity, according to nutritionist Lin Li-cen. She noted a case of a 50-year-old woman with high insulin resistance who consistently slept from 4 to 6 a.m., initially dismissing the link between late nights and blood sugar.

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Late sleep not only affects sleep but also impacts blood sugar metabolism. Sleeping too late can interfere with circadian rhythms, hormones, insulin sensitivity, and eating times, leading to unstable blood sugar.

Lin explained that the body is less efficient at processing sugars at night. Insufficient sleep, including fragmented sleep, can decrease insulin sensitivity by 20% to 30%, making it harder for cells to utilize glucose. A large generational study published in JAMA Network Open found that individuals sleeping less than six hours nightly face a higher risk of type 2 diabetes compared to those sleeping seven to eight hours.

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The body is less adept at processing sugar at night. Insulin sensitivity and glucose tolerance are better in the morning; they decline as the night progresses. This means blood sugar is more likely to rise and fall more slowly at night.

Furthermore, lack of sleep elevates stress hormones like cortisol, which prompts the liver to release more glucose, leading to unstable fasting and nighttime blood sugar. Late sleepers also tend to have later dinners and consume more sugary snacks and drinks, further complicating blood sugar control. Eating high-carbohydrate foods when melatonin levels rise for sleep also results in poorer glucose processing.

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Lack of sleep makes cells less responsive to insulin, making it harder to move blood sugar into muscles, liver, and fat cells for use. Studies show insulin sensitivity may drop by 20%–30%.

Lin emphasizes that the combination of reduced insulin sensitivity, elevated stress hormones, and late-night eating habits can increase insulin resistance and the risk of type 2 diabetes over time. She recommends adopting an earlier dinner schedule, ensuring at least seven hours of sleep, and going to bed earlier to support better blood sugar metabolism and weight management.

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When sleep-deprived or staying up late, the body remains in a heightened state of alertness, with increased sympathetic nervous system and cortisol activity. High cortisol levels promote glucose release from the liver, making fasting or nighttime blood sugar more unstable.