Evidence check: Cortisol in the context of blood sugar

Cortisol, the primary stress hormone, can raise blood glucose through several mechanisms: it stimulates gluconeogenesis in the liver, inhibits insulin secretion, and promotes insulin resistance in peripheral tissues. Chronically elevated cortisol – due to ongoing stress or Cushing's syndrome – is therefore associated with impaired glucose tolerance and increased diabetes risk. However, the evidence for direct genetic testing of cortisol in the context of blood sugar in consumer tests is weak. Most tests analyze single SNPs in cortisol-related genes (e.g., NR3C1, FKBP5), but effect sizes are small and often not replicated. Moreover, cortisol levels are heavily influenced by time of day, diet, sleep, and psychosocial factors – a genetic test alone cannot reliably predict actual blood sugar impact. The evidence level is best described as mechanistic to unclear: the basic physiology is plausible, but predictive power for individuals is minimal. Consumer tests that derive personalized dietary advice from such SNPs overstep the scientific basis.