If your blood sugars have changed and you have thyroid symptoms like nervousness, feeling hot or cold, tiredness or difficulty sleeping, have your thyroid checked. If you have a low thyroid level and are placed on thyroid medication, you will probably need to raise your insulin doses slightly to control your blood sugars, especially if you have adjusted your insulin doses downward as your thyroid became less active. When some aspects of your external environment change, your body adjusts by changing its use of glucose and fat. In hot weather the body uses more energy in cooling itself. It increases circulation to send more blood flow to the skin, which picks up insulin faster from an injection or infusion site, and speeds up the action of insulin.
Most people are more active in the summertime and have less fat in their diet, as well.
As these things happen, less background insulin may be needed to keep the blood sugar controlled during the summer, while just the opposite happens over the winter months. Metabolism increases in two other circumstances, creating a need for you to lower your background insulin. If you are outside during very cold weather and find yourself shivering, your control may be better with less insulin. Similarly, at higher altitudes more energy is needed to breath and pump blood as the air becomes thinner, especially in the first few days after you arrive at a higher elevation. Until the body acclimates, less long-acting insulin or more carbohydrate may be required.