Why do blood glucose levels fluctuate throughout the day in diabetics on treatment?

Why Blood Sugar Fluctuates During the Day in Diabetics on Treatment

Blood sugar fluctuates throughout the day in diabetics on treatment primarily due to circadian rhythm effects, with glucose levels typically being higher in the evening and at night compared to morning, even with identical meals and insulin doses. 1

Physiological Factors Causing Blood Glucose Fluctuations

Circadian Rhythm Effects

• Research shows that glucose concentrations are significantly higher at night than during the day, even when identical meals are consumed 1
• In patients with gestational diabetes, glucose concentrations were higher at dinner compared to breakfast and lunch, despite identical meals 1
• Time of day has been found to be independently associated with glucose levels, with the rate of glucose decline being greater in the morning than at night 1

Insulin Physiology and Administration

• Basal insulin requirements vary throughout the day due to natural hormonal fluctuations 1
• The dawn phenomenon (increase in blood glucose in early morning hours) is caused by counter-regulatory hormones such as cortisol and growth hormone 1
• Insulin sensitivity varies throughout the day, with many people requiring more insulin per carbohydrate in the mornings when counter-regulatory hormones are still high 1

Meal Composition and Timing

• Carbohydrate intake is the major determinant of glycemic response 2
• Protein has minimal effect on blood glucose with adequate insulin, but with insulin deficiency, gluconeogenesis proceeds rapidly 2
• Fat has little direct effect on blood glucose levels but can contribute to insulin resistance with high intake 2

Factors Affecting Daily Blood Glucose Variability

Activity and Exercise

• Exercise increases the rate of insulin absorption from injection sites by increasing blood flow to the skin 1
• Physical activity can lower blood glucose levels, requiring adjustment of insulin doses or carbohydrate intake 1

Insulin Administration Variables

• Absorption rates differ between subcutaneous and intramuscular sites, with intramuscular being faster 1
• Areas of lipohypertrophy (thickened tissue from repeated injections) show slower absorption 1
• Different body sites have variable absorption rates: abdomen (fastest), followed by arms, thighs, and buttocks 1

Stress and Illness

• Emotional disturbances, stress, and illness can alter insulin requirements 3
• During illness, it's important to continue insulin even if the patient is unable to eat or is vomiting 1

Medication Timing and Dosing

• Insulin dosage adjustments should be based on blood glucose measurements due to day-to-day variability 1
• For patients on once-daily basal insulin with persistent overnight hyperglycemia, changing administration time from evening to morning may help 4

Special Considerations

Meal-Related Fluctuations

• Postprandial glucose concentrations after morning meals may be significantly higher at 1 hour but lower from 3-9 hours compared to evening meals 1
• The impairment of glucose tolerance in the afternoon seems to increase as the clinical condition of the patient deteriorates 1

Monitoring Recommendations

• Self-monitoring of blood glucose (SMBG) is essential for patients on insulin therapy 1
• Most patients with type 1 diabetes or on intensive insulin regimens should test before meals and snacks, occasionally postprandially, at bedtime, before exercise, and when hypoglycemia is suspected 1
• For many patients, this requires testing 6-8 times daily, though individual needs may vary 1

Clinical Implications and Management

Adjusting Treatment Based on Patterns

• Basal insulin should be adjusted every 3 days to achieve target fasting glucose levels (80-130 mg/dL) without hypoglycemia 4
• For persistent nocturnal hyperglycemia, consider longer-acting basal analogs (U-300 glargine or degludec) 4
• Watch for signs of overbasalization (high bedtime-to-morning glucose differential ≥50 mg/dL) 4

Avoiding Hypoglycemia

• Hypoglycemia is the most common adverse reaction of insulin therapy 3
• Risk factors include missed meals, alcohol consumption, and certain medications 3
• Patients should be educated on hypoglycemia recognition and always carry quick-acting carbohydrates 4

Common Pitfalls in Managing Blood Glucose Fluctuations

• Failing to recognize that glucose response varies by time of day, even with identical meals 1
• Not adjusting insulin doses based on patterns of glucose fluctuation 4
• Overlooking the impact of exercise, stress, or illness on insulin requirements 1, 3
• Continuing to inject insulin in areas of lipohypertrophy, leading to unpredictable absorption 1
• Not accounting for the dawn phenomenon when setting basal insulin rates 1

Understanding these factors and patterns can help diabetic patients and their healthcare providers better manage blood glucose fluctuations throughout the day, leading to improved glycemic control and reduced risk of complications.