Cancer treatment requires careful management of metabolic health. Chemotherapy and supporting medications can significantly disrupt the body’s ability to regulate glucose, often leading to hyperglycemia (high blood sugar). This high blood sugar can interfere with treatment effectiveness and recovery. Stable blood sugar control is important for reducing complications like infection risk, improving wound healing, and supporting overall resilience during treatment.
Why Chemotherapy Affects Blood Sugar Levels
The most frequent cause of elevated blood sugar during chemotherapy is the use of corticosteroids, such as dexamethasone or prednisone. These are often prescribed to prevent allergic reactions or manage nausea. Corticosteroids promote insulin resistance, making the body’s cells less responsive to insulin. They also increase the liver’s production of glucose, leading to significant blood sugar spikes and sometimes causing temporary, new-onset diabetes.
Beyond supportive medications, some chemotherapy agents, such as L-asparaginase, 5-fluorouracil (5-FU) regimens, and platinum-based agents like cisplatin, can directly impact glucose metabolism. The physiological stress of cancer and treatment contributes to inflammation, further impairing insulin function. Uncontrolled pain and the release of stress hormones, such as cortisol, also raise blood sugar levels, complicating metabolic control.
Optimizing Diet and Hydration During Treatment
Nutrition is a key factor patients can control to stabilize glucose levels during treatment. Consistent meal timing is important, as irregular eating patterns can cause unpredictable sugar spikes and crashes. Instead of two or three large meals, eat five or six smaller, nutrient-dense meals throughout the day. This maintains a steady energy supply and is often easier to tolerate with chemotherapy side effects.
Prioritize complex carbohydrates with a low glycemic index, such as whole grains, oats, and non-starchy vegetables. These foods break down slowly, preventing the rapid glucose surges associated with refined sugars. Pairing carbohydrates with protein and healthy fats, such as almonds or plain yogurt, further slows digestion and stabilizes blood sugar.
Hydration is also important for glucose management. High blood sugar causes increased urination, which can lead to dehydration. Maintaining a steady intake of water, clear broths, or sugar-free beverages helps the kidneys flush out excess glucose. Working with a registered dietitian familiar with both cancer and diabetes management can provide personalized strategies for coping with side effects like nausea and reduced appetite.
Strategies for Glucose Monitoring and Medication Adjustment
Frequent and accurate glucose monitoring is necessary to safely manage blood sugar during chemotherapy, especially when steroids are used. Patients should establish an appropriate testing schedule with their healthcare team, often checking levels before meals, at bedtime, and more frequently on treatment days. Maintaining a detailed log of blood sugar readings, medication doses, and food intake provides the care team with the data needed for informed adjustments.
While target ranges are individualized, general goals for fasting blood glucose may be slightly higher than usual for patients with pre-existing diabetes (100 to 130 mg/dL). For patients without a diabetes history, the goal is typically 75 to 121 mg/dL. Continuous glucose monitors (CGMs) can provide real-time data and identify trends missed by finger-stick checks.
Adjustments to existing diabetes medications are almost always necessary during chemotherapy cycles. For instance, a patient taking once-daily corticosteroids like prednisolone may require intermediate-acting insulin to manage the delayed blood sugar spike, which occurs about eight hours after the dose. Longer-acting steroids, such as dexamethasone, may necessitate long-acting insulin to moderate glucose levels throughout the day. All changes to insulin or oral diabetes medications must be guided and approved by the oncology or endocrinology team to prevent dangerous fluctuations.
Identifying and Addressing High-Risk Situations
Two high-risk situations require immediate attention: severe hyperglycemia and hypoglycemia. Severe high blood sugar (hyperglycemia) is indicated by symptoms such as excessive thirst, frequent urination, fatigue, and blurred vision. Persistently elevated glucose levels, particularly readings consistently above 300 mg/dL, require prompt medical evaluation. Uncontrolled hyperglycemia risks leading to life-threatening conditions like diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS).
Hypoglycemia (low blood sugar) is also a serious concern, especially for patients taking insulin who have poor appetite or nausea. Warning signs include shakiness, confusion, rapid heartbeat, and sweating. If a blood sugar reading falls below 70 mg/dL, patients should immediately consume a source of fast-acting glucose, such as four ounces of juice or glucose tablets, to raise the level quickly. Any reading below 70 mg/dL or consistently above 300 mg/dL is an emergency and warrants contacting the medical team immediately.
Urgent situations also include persistent vomiting or diarrhea that prevents normal eating or drinking, as this complicates glucose and hydration balance. Clear communication with the healthcare team about any new or worsening symptoms is essential for safety throughout the chemotherapy process.