High Blood Sugar and Breast Cancer: What to Know

High blood sugar (hyperglycemia) can matter for people with breast cancer, but the level of concern usually depends on how high and how persistent it is, and whether you’re on treatments that raise glucose. Too much sugar and excess calories can raise insulin and related hormones, which may encourage tumor growth, so limiting added sugars is generally a good idea. ^[1] Problems with insulin like chronic high blood sugar, high insulin levels, or insulin resistance can increase the risk of developing breast cancer and other cancers. ^[2]

Why Blood Sugar Matters in Breast Cancer

• Glucose fuels all cells healthy and cancer cells so the issue isn’t sugar alone but consistently high insulin and glucose levels. ^[1]
• Chronic hyperglycemia and insulin resistance are linked with higher cancer risk and may affect outcomes, which is why stable blood sugar is encouraged during and after treatment. ^[2]

How Cancer Treatments Can Raise or Lower Blood Sugar

• Chemotherapy can cause nausea, vomiting, mouth sores, and appetite loss, which sometimes leads to low blood sugar if you can’t eat well. ^[3]
• Steroids often given with chemotherapy to prevent nausea can raise blood sugar significantly, even in people without diabetes. ^[4]
• Radiation and hormone therapies can also affect energy, appetite, and activity, indirectly impacting blood sugar control. ^[3]

Practical Targets and Monitoring

• Managing blood sugar during cancer care can lower infection risk and support overall recovery, so it shouldn’t take a back seat during treatment. ^[5]
• People undergoing cancer treatment sometimes experience glucose readings above 200 mg/dL, and many report difficulty keeping glucose controlled without clear guidance so proactive monitoring is helpful. ^[6]

Nutrition Tips That Help

• Limiting added sugars and total calories helps keep insulin levels in check; many people benefit from cutting sweet drinks and ultra-processed sweets. ^[1]
• Global recommendations often suggest capping added sugars per day to reduce metabolic strain. ^[7]

When High Blood Sugar Is Urgent

• Very high readings (for example, above ~250–300 mg/dL) or symptoms like excessive thirst, frequent urination, vomiting, or confusion need prompt medical advice, especially if you’re receiving steroids. ^[4]
• Cancer treatment protocols in other settings show that therapy may be paused until glucose is lowered and medications like insulin may be needed; severe cases such as diabetic ketoacidosis require urgent care. ^[8]

Action Steps You Can Take

• Track glucose regularly, especially during chemotherapy weeks or when taking steroids, and share readings with your oncology team. ^[3]
• Use a balanced meal plan with protein, fiber, and healthy fats to smooth glucose spikes; small, frequent meals can help on low‑appetite days. ^[3]
• Coordinate diabetes care with oncology this joint approach improves safety and may reduce complications during treatment. ^[9]

Bottom Line

• You don’t need to panic, but consistent high blood sugar deserves attention in breast cancer, because insulin and glucose balance can influence risk and treatment experience. ^[1]
• With mindful diet choices, monitoring, and coordination with your care team especially around steroid use you can usually keep blood sugar in a safer range during treatment. ^{[5] [4]}