What is the Somogyi effect and how is it managed in diabetes?

The Somogyi Effect: A Largely Discredited Phenomenon

The Somogyi effect—the theory that nocturnal hypoglycemia causes rebound fasting hyperglycemia—has been conclusively disproven by modern continuous glucose monitoring studies and should not guide clinical decision-making in diabetes management. 1, 2, 3

What Was Originally Proposed

The Somogyi effect was a hypothesis suggesting that:

• Nocturnal hypoglycemia (low blood sugar during sleep) triggers counter-regulatory hormone release (glucagon, epinephrine, cortisol, growth hormone) 2
• These hormones cause excessive glucose production, leading to rebound hyperglycemia (high blood sugar) in the morning 2
• This supposedly explained why some patients had high fasting glucose despite receiving insulin 3

What the Evidence Actually Shows

The Reality is the Opposite

Multiple high-quality studies demonstrate that nocturnal hypoglycemia is followed by lower, not higher, fasting glucose levels: 1, 2, 3

• A 2022 study of 2,600 patients with type 2 diabetes using continuous glucose monitoring found morning fasting glucose was significantly lower after nights with nocturnal hypoglycemia compared to nights without hypoglycemia (P < 0.001) 1
• The nocturnal glucose nadir was directly correlated with fasting glucose levels (r = 0.613, P < 0.001), meaning lower overnight glucose predicted lower morning glucose 1
• A landmark 1987 study in the New England Journal of Medicine found that after induced nocturnal hypoglycemia (36 mg/dL), 8 AM glucose levels were 113 mg/dL compared to 182 mg/dL when hypoglycemia was prevented 2
• Regression analysis showed fasting glucose was directly (not inversely) related to the nocturnal glucose nadir (r = 0.761, P = 0.011) 2

How Rare Are True Rebound Episodes?

The Somogyi effect is extraordinarily rare in clinical practice:

• In the 2022 study, only 84 cases out of 4,705 nights showed fasting glucose >7 mmol/L (126 mg/dL) after nocturnal glucose <3.9 mmol/L (70 mg/dL) 1
• Only 27 cases showed fasting glucose >7 mmol/L after severe nocturnal hypoglycemia <3.0 mmol/L (54 mg/dL) 1
• A 2013 UK study found only 2 instances of fasting glucose >10 mmol/L (180 mg/dL) after nocturnal hypoglycemia, both likely after treatment of the hypoglycemic episode 3
• When fasting glucose was ≤5 mmol/L (90 mg/dL), there was evidence of nocturnal hypoglycemia on 94% of nights 3

Clinical Implications for Fasting Hyperglycemia

If a patient presents with high fasting glucose, nocturnal hypoglycemia is extremely unlikely to be the cause:

• Fasting glucose values >9.6 mmol/L (173 mg/dL) were associated with no risk of nocturnal hypoglycemia 1
• Fasting glucose values <3.9 mmol/L (70 mg/dL) were associated with 100% risk of preceding nocturnal hypoglycemia 1
• The 2013 study confirmed that fasting glucose <5 mmol/L (90 mg/dL) is an important indicator of preceding silent nocturnal hypoglycemia 3

Post-Hypoglycemic Nocturnal Hyperglycemia: A Different Phenomenon

A 2025 study identified a distinct pattern called post-hypoglycemic nocturnal hyperglycemia (PHNH) that differs from the classic Somogyi effect:

• PHNH occurred in 32.8% of type 1 diabetes patients during a 14-day monitoring period 4
• Patients with PHNH were younger, used higher total daily insulin doses, and had poorer overall glycemic control 4
• These patients had longer time above range, shorter time in range, higher glucose variability, and more diurnal hypoglycemia 4
• This represents aggressive insulin dosing causing both hypoglycemia and hyperglycemia, not a physiologic rebound phenomenon 4

How to Manage Fasting Hyperglycemia

When encountering elevated fasting glucose, the appropriate response is:

• Do not reduce basal insulin based on fear of nocturnal hypoglycemia if fasting glucose is consistently elevated 1, 3
• Use continuous glucose monitoring or structured self-monitoring to assess actual nocturnal glucose patterns 5
• If fasting glucose is >180 mg/dL (10 mmol/L), nocturnal hypoglycemia is not the cause—increase basal insulin 1
• If fasting glucose is <90 mg/dL (5 mmol/L), investigate for nocturnal hypoglycemia and consider reducing basal insulin 3
• Titrate basal insulin based on fasting glucose targets of 80-130 mg/dL (4.4-7.2 mmol/L) 5, 6

Common Clinical Pitfalls

The persistence of the Somogyi myth in clinical practice leads to:

• Inappropriate withholding or reduction of necessary basal insulin when patients have high fasting glucose 3
• Failure to adequately treat fasting hyperglycemia due to unfounded concerns about nocturnal hypoglycemia 1
• Missed opportunities to optimize overnight insulin coverage 3
• Patients and clinicians remaining reluctant to increase insulin doses despite clear evidence of inadequate basal coverage 3

The evidence is clear: asymptomatic nocturnal hypoglycemia does not cause clinically important fasting or daytime hyperglycemia in patients with diabetes on usual therapeutic regimens. 2, 7